CA2071595C

CA2071595C - Method and apparatus for recording compressed audio data on a video recording medium

Info

Publication number: CA2071595C
Application number: CA002071595A
Authority: CA
Inventors: Hajime Inoue; Keiji Kanota; Yukio Kubota
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1991-06-25
Filing date: 1992-06-18
Publication date: 2001-09-04
Anticipated expiration: 2012-06-18
Also published as: CA2071595A1; DE69213579T2; JPH052833A; JP3508138B2; DE69213579D1; EP0520444A2; EP0520444B1; US5424850A; EP0520444A3

Abstract

Video and audio data are recorded onto video and audio signal recording areas of a track of a record medium, these areas being included either in one of several segments in the track or the track being comprised of only a single segment of video and audio signal recording areas. Audio data that is supplied at substantially the same time as the video data is compressed and recorded in a first audio sector of the audio signal recording area. Then, depending upon whether a first or second audio signal recording mode is selected, either compressed audio data which is derived from the audio data supplied at substantially the came time as the video data or independent compressed audio data is provided. The derived or independent compressed audio data is recorded in a second audio sector of the audio signal recording area.

Description

2x71595 PATENT

METHOD AND APPARATUS FOR RECORDING COMPRESSED AUDIO DATA
ON A VZbEO RECORDING MEDIUM
BACKGROUND OF THE INVENTION
This invE:ntion relates to video signal recording and, more part~.cu~.arly, to a method and apparatus for recording compressed audio data along w.i.th the video data on a record medium, such as a digital video tape.
Digital signal recording apparatus, such as digital vide~~ tape recorders (DVTR) h<~ve been developed far broadcasting purpnses because of the excel:Lenc quality in video pictures that are :.-eproduced therefrom. Heretofore, the emphasis of such d~.gi~~al video recording systems has been on enhancing the video picture. Typically, analog vwdeo signals are digitized by samp_Ling the analog signal and converting each sample to an 8-bit digital signal. Max~.mum video ~,nfo.rmatian is retained by recording the 8-bit video samples in uncompressed form.
ConsE:quently, a substantial amount of record medium is needed to record video programs of even minimal broadcasting length, such as thirty minute programs.
DVTR systems have been developed with two distinct formats: the so--ea:Lled component type digital recorder, known as the D-1 format, and the so--called composite type digztal recorder, known as the D-2 format. G7hen recording digital v~.deo signals on video tape using the D-1-format, an audio recording sector is provided =~n the middle of a track and zs preceded and 2~1~:~~~~
PATENT

1 followed by video recording sectors. Up to four channels of 2 audio information may be recorded in the audio sector. By 3 providing the audio sector in the middle of the track, it is 4 expected that the usual scanning heads will exhibit stable track following, or tracking control, by the time those heads reach the 6 middle of the track during normal as well as special effect 7 scanning speeds. It has been found that small scanning errors 8 that may be present when the video sectors are scanned may be 9 more easily corrected and are less perceptible to a human observer than if those same small scanning errors are present 11 when audio information is scanned. By locating the audio 12 information in the middle of a track, such small scanning errors 13 that may be present when audio information is reproduced are 14 minimized.
When video and audio information are recorded in the 16 D-2 format, the audio information is recorded in audio sectors 17 that precede and follow the video sector. The video sector is, 18 of course, substantially larger than each of the audio sectors, 19 and two channels of audio information may be recorded in each audio sector. Thus, a total of four channels of audio 21 information may be recorded in the D-2 format, with two channels 22 of audio information preceding the video sector and two channels 23 of audio information following the video sector. The track 24 length of the D-2 format is shorter than the track length. of the D-1 format by approximately 13%. As a result of this shorter 2~~~~9~
PATENT

1 track length, tracking control errors are minimized over the 2 entire length of the track and, thus, the flanking audio sectors 3 are scanned quite stably even when different tape speeds are used 4 to effect different reproducing modes (e. g. normal, slow speed, high speed and special effects modes).
6 The four-channel audio recording capability of the D-1 7 and D-2 formats facilitates the recording of audio information 8 with high quality. If audio information normally is recorded as 9 two-channel audio data (e. g. left and right audio channels), then the same two-channel audio data may be recorded twice so as to be 11 recorded as four-channel audio data. Such redundant recording is 12 most helpful in overcoming or correcting errors that otherwise 13 would result from drop-out in one or the other pairs of audio 14 channels. Four-channel audio recording also facilitates a technique known as "after-recording", in which audio information 16 that is produced at a later time (i.e. subsequent to the 17 recording of video information) may be recorded. For example, 18 when audio information is edited or when audio information is 19 translated into a different language, such edited or translated audio data usually is provided at a time that is substantially 21 delayed from the time that the video information is recorded.
22 Nevertheless, this after-recorded audio data is recorded quite 23 easily in two of the four audio channels that are available for 24 recording.

20'~~.~~~
PATENT

1 As mentioned above, digital video recording for 2 broadcasting purposes is accomplished without compression of the 3 video or audio data. While this assures a high quality of video 4 information, the fact that the video data is uncompressed means that a substantial amount of record medium must be used to 6 accommodate such uncompressed video data. Since video tapes must 7 be of finite length, the need for more record medium to record 8 uncompressed video data results in a shorter overall recording 9 time. This inefficient use of video tape is an acceptable trade-off for broadcasting purposes but is not acceptable for consumer 11 use. A desirable objective of video tape recording is the 12 capability of recording a broadcasted program in the user's 13 absence. Since a consumer may use his video recorder to record 14 several programs, it is important that commercially available "blank" magnetic tape (such as in cassette form) be of sufficient 16 length to record the many programs that the user otherwise may 17 miss. Hence, for consumer use, a desirable objective is to 18 record video and audio data on a single record medium over a long 19 period of time.
To accommodate long recording periods, digital video 21 recorders for consumer use have been developed to record a 22 channel of audio data at a sampling rate of 48 KHz, with each 23 audio sample being digitized as a 16-bit sample. Such consumer-24 type digital video recorders typica-lly are capable of recording only two audio channels; and, as a result, if errors are present _4_ 2~~~~~~
PATENT

1 in the recorded audio information, it is difficult to correct 2 such errors. Thus, it is difficult to obtain high quality audio 3 recording in such two-channel consumer-type video recorders.
4 Furthermore, the typical consumer-type two-channel audio recording capability does not easily permit the after-recording 6 of audio information.

8 Therefore, it is an object of the present invention to 9 provide an improved video recorder that is particularly adapted for consumer use and which permits high quality as well as after-11 recording of audio information.
12 Another object of this invention is to provide a 13 digital video recorder that is particularly adapted to record 14 long periods of video programs while permitting audio information to be recorded with high quality as well as at a time subsequent 16 to the recording of the video information.
17 A further object of this invention is to provide an 18 improved method and apparatus for recording video and audio data 19 onto video and audio signal recording areas of a track of a record medium, which overcome the aforenoted drawbacks and ?1 disadvantages of the prior art, and which are particularly ?2 adapted for consumer use.
'-3 An additional object of this invention is to provide a ?4 technique for recording four channels of compressed audio data on ?5 the same record medium as are recorded video data, with the four PATENT

1 channels being used either for recording audio information with 2 high quality or for permitting the after-recording of audio data.
3 Various other objects, advantages and features of the 4 present invention will become readily apparent from the ensuing detailed description, and the novel features will be particularly 6 pointed out in the appended claims.

8 In accordance with this invention, a method and 9 apparatus for recording audio data together with video data onto audio and video signal recording areas of a track of a record 11 medium are provided. Input audio data that is supplied at 12 substantially the same time as the video data is compressed and 13 recorded in a first audio sector. Depending upon whether a first 14 or a second audio signal recording mode is selected, either compressed audio data that is derived from the input audio data 16 or independent compressed audio data is provided and recorded in 17 a second audio sector.
18 The audio and video signal recording areas may be 19 included in one of a plurality of recording segments in a track or, alternatively, these recording areas may comprise the only 21 audio and video areas in the track.
22 As one aspect of this invention, the compressed audio 23 data which is derived from the input audio data is provided by 24 determining an error in the compressed input audio data, and then compressing that error. As a feature of this aspect, the error 2~~~~~~
PATENT

1 in the compressed input audio data is determined by digitizing an 2 input analog audio signal, compressing that digitized audio data, 3 expanding the compressed, digitized audio data, converting the 4 expanded audio data to analog form, determining a difference between the converted analog audio data and the input analog 6 audio data, and digitizing the determined difference.
7 As another embodiment for determining an error in the 8 compressed input audio data, said compressed input audio data is 9 expanded and a difference between that expanded audio data and ZO the digitized input analog audio signal is determined.
11 As yet another aspect of this invention, compressed 12 audio data that is derived from the input audio data supplied at 13 substantially the same time as the video data is provided by 14 supplying the same compressed audio data for recording in both the first and second audio sectors, thereby recording redundant, 16 compressed audio data in both audio sectors.
17 The present invention also is directed to a method and 18 apparatus for reproducing the audio data that is recorded in the 19 aforementioned manner in the audio sectors described above.
BRIEF DESCRIPTION OF THE DRAWINGS
21 The following detailed description, given by way of 22 example, and not intended to limit the present invention solely 23 thereto, will best be understood in conjunction with the 24 accompanying drawings in which: -_7_ _ 2071595 PATENT

1 FIG. 1 is a block diagram of digital video recording 2 apparatus in which the present invention finds ready application;
3 FIG. 2 is a schematic representation of a segment (or 4 track) in which video and audio data are recorded;
FIG. 3 is a block diagram of one embodiment of 6 recording apparatus in accordance with the present invention:
7 FIG. 4 is a block diagram of digital video reproducing 8 apparatus for recovering digital audio and video information that 9 may be recorded by the apparatus shown in FIG. 1;
FIG. 5 is a block diagram of one embodiment of audio 11 reproducing apparatus that is compatible with the recording 12 apparatus shown in FIG. 3;
13 FIG. 6 is a block diagram of another embodiment of 14 audio recording apparatus which incorporates the present invention;
16 FIG. 7 is a block diagram of audio reproducing 17 apparatus that is compatible with the embodiment shown in FIG. 6;
18 FIG. 8 is a block diagram of yet another embodiment of 19 audio recording apparatus which incorporates the present invention;
21 FIG. 9 is a block diagram of audio reproducing 22 apparatus that is compatible with the embodiment shown in FIG. 8;
23 and _g_ 2~~~~~~
PATENT

1 FIG. 10 is a schematic representation of yet another 2 segment in which video and audio data are recorded in accordance 3 with the present invention.

Referring now to the drawings, wherein like reference 6 numerals are used throughout, FIG. 1 is a block diagram of 7 digital video/audio recording apparatus in which the present 8 invention finds ready application. As an example, the video 9 recording apparatus shown in FIG. 1 may be used directly with a video camera and may be incorporated in the same housing 11 therewith, such as a so-called "camcorder". Alternatively, the 12 apparatus of FIG. 1 may be supplied with video signals recovered 13 from broadcasted or previously recorded television signals. In 14 any event, the illustrated apparatus is comprised of an information extractor 2, a frequency converter 3, a line 16 sequencer 4, image block converters 5 and 6, a data compressor 8, 17 a mixer 14, an audio processor 15 and recording heads 13a and 18 13b. Information extractor 2 is coupled to input terminals lY, 19 lU and 1V and is adapted to receive a digital luminance signal Y
and digital color difference signals U and V, respectively. In 21 one embodiment, the digital luminance and color difference 22 signals are derived from the three primary color signals red, 23 green and blue produced by a color video camera. Alternatively, 24 the digital luminance and color difference signals are derived from reproduced television signals or from broadcasted television _g_ 20~1~~~
PATENT

1 signals. It will be appreciated that the derivation of digital 2 luminance and color difference signals Y, U and V and the 3 application of these signals to information extractor 2 are 4 conventional and further description thereof need not be provided.
6 The information extractor functions to extract useful 7 luminance and color difference information from the digital 8 luminance and color difference signals supplied thereto and to 9 discard the usual video signals which do not comprise useful video information. For example, signals that are included in 11 line intervals which typically are not displayed on a 12 conventional television monitor as well as various synchronizing 13 and equalizing signals are discarded. Information extractor 2 '14 includes output terminals to which the extracted digital luminance signal Y and the extracted digital color difference 16 signals U and V are supplied, respectively.
17 Frequency converter 3 is coupled to information 18 extractor 2 and is adapted to convert the sampling frequency, or 19 data rate, of the digital luminance signal Y. The sampling frequency of this luminance signal may be on the order of 13.5 21 MHz; and the frequency converter is adapted to reduce that 22 frequency to approximately three-fourths (3/4) of its original 23 sampling frequency. As will be known by those of ordinary skill 24 in the art, frequency converter 3 may be implemented by a thin-out filter that prevents aliasing noise. The frequency-converted '~Or~~.~~~
PATENT

1 digital luminance signal Y is supplied from frequency converter 3 2 to image block converter 5.
3 The output terminals of information extractor 2 to 4 which the extracted digital color difference signals U and V are supplied are coupled to line sequences 4. The line sequences is 6 adapted to reduce the sampling frequency, or data rate, of each 7 of the digital color difference signals U and V to one-half (1/2) 8 of its original sampling frequency and to select alternate ones 9 of these frequency-reduced color difference signals on a line-by-line basis. For example, one line of the frequency-reduced 11 digital color difference signal U is followed by the next line of 12 the frequency-reduced color difference signal V. Thus, line-13 sequential, frequency-reduced digital color difference signals U

14 and V are produced by line sequences 4. These line sequential, frequency-reduced color difference signals are supplied to image 16 ' block converter 6.
17 Image block converters 5 and 6 are adapted to form 18 blocks of frequency-reduced video signals supplied thereto from 19 frequency converter 3 and line sequences 4, respectively. For example, a predetermined number of samples is arranged as an 21 image block by each of these image block converters. As 22 illustrated, image block converters 5 and 6 are coupled to a 23 composing circuit 7 which operates to form a single channel of 24 digital video data from the block o~ frequency-reduced digital luminance signals and from the block of frequency-reduced, line ~0~1~9~
PATENT

1 sequential color difference signals produced by the respective 2 block converters. Composing circuit 7 is coupled to data 3 compressor 8 which is adapted to compress the data included in 4 the single channel of video information composed by the composing circuit. For example, data compressor 8 may comprise an 6 orthogonal transform circuit, such as a discrete cosine transform 7 circuit, or it may comprise an adaptive dynamic range coder 8 (ADRC), or other known circuits. As a result, the amount of data 9 needed to represent the original luminance and color difference signals is reduced, 11 The output of data compressor 8 is coupled to a framing 12 circuit 9 which operates to convert the clock frequency of the 13 data-compressed frequency-reduced luminance and color difference 14 signals to a clock rate that is particularly compatible for recording. In addition, the framing circuit converts the block 16 structure format produced by image block converters 5 and 6, 17 composing circuit 7 and data compressor 8 to a frame structure 18 data format.
19 Framing circuit 9 is coupled to mixer 14 by way of a parity generator 10. The parity generator operates in 21 conventional manner to generate parity bits from the frames of 22 compressed data supplied thereto by framing circuit 9, these 23 parity bits being used for error correction purposes during a 24 reproduction operation. Mixer 14 i-s supplied with compressed audio signals from audio processor 15 in a manner to be described ~0~~~9~
PATENT

1 below. One embodiment of the audio processor is illustrated in 2 FIG. 3, and will be explained hereinafter. Suffice it to say . 3 that audio processor 15 is supplied with audio signals, such as 4 analog audio signals, by way of input terminals lA and 1B. In particular, the audio signals supplied to input terminal lA
6 preferably are comprised of two-channel audio signals (e. g.
7 stereo signals), and these audio signals are supplied to terminal 8 lA at substantially the same time as video data is supplied to 9 input terminals lY, lU and 1V. As will be described, audio signals may be coupled to input terminals 1B to effect an after-11 recording mode of operation.
12 Mixer 14 serves to combine the video data supplied 13 thereto from framing circuit 9 and parity generator 10 with audio 14 data supplied thereto by audio processor 15 and to couple the combined, or mixed video and audio information to a channel 16 encoder 11. The channel encoder operates to reduce the low 17 frequency components of the video and audio data to be recorded 18 and may encode the video and audio data in conventional manner 19 and in accordance with typical recording codes, such as 1,7 code, MFM code, NRZI, etc. The output of channel encoder 11 is coupled 21 to recording heads 13A and 13B by way of recording amplifiers 12A
22 and 12B, respectively.
23 The video recording apparatus illustrated in FIG. 1 may 24 be of conventional construction known to those of ordinary skill in the art. Accordingly, in the interest of simplicity and 2~~~~~~
PATENT

1 brevity, further description of such recording apparatus is not 2 provided. The present invention is directed more particularly to 3 audio processor 15; and preferred embodiments of this audio 4 processor are described below in conjunction with, for example, FIGS. 3, 6 and 8. However, for the purpose of the present 6 description, it should be appreciated that the mixed video and 7 audio data provided by mixer 14 are recorded in one or more 8 segments of a record track in accordance with the format 9 schematically illustrated in FIG. 2. In one embodiment, a plurality of segments of the type shown in FIG. 2 are recorded in 11 a single track on the record medium, such as a single track of 12 video tape. In another embodiment, the segment shown in FIG. 2 13 comprises substantially the entire track.
14 As shown, a video signal recording area, identified as "video sector", is followed by two successive audio signal 16 recording areas, identified as °'audio sector 1" and "audio sector 17 2'°. It will be recognized that the video and audio sectors shown 18 in FIG. 2 are not drawn to scale.
19 Preceding each sector is a preamble area and a margin area, the preamble area having data and synchronizing information 21 recorded therein and the margin area being provided to permit 22 change-over in the reproducing apparatus as well as to 23 accommodate tolerances in the recording of video and audio 24 information. Each sector is followed by a postamble area; and it is seen that adjacent sectors are separated by a region comprised PATENT

1 of a postamble area, a margin area and a preamble area. The 2 signals recorded in the preamble and postamble areas preferably 3 are comprised of pulses having a repetitive frequency equal to 4 the clock frequency (or data bit frequency) of the respective video and audio data recorded in the video and audio sectors.
6 Alternatively, the pulse signals may exhibit a frequency that is 7 a multiple or submultiple of such data bit frequency. The 8 purpose of these pulse signals is to enable a phase locked loop 9 (PLL) to lock onto the data bit frequency during a reproducing mode such that the clock frequency of the reproducing apparatus 11 is synchronized to the clock frequency of the information being 12 reproduced from the record medium.
13 One embodiment of audio processor 15 which is 14 particularly adapted for recording four channels of audio information now will be described in conjunction with the block 16 diagram shown in FIG. 3. This audio processor is adapted to 17 operate in one of two different audio signal recording modes: a 18 high quality mode, in which two-channel audio information is 19 recorded in four channels, or an after-recording mode, in which two-channel audio information is recorded substantially 21 simultaneously with the video information, and different two-22 channel audio information is recorded at a later time, subsequent 23 to the recording of the video information, thus constituting 24 "after-recorded" audio data. A se hctor switch 47 is used to 20~1~95 PATENT

1 select either the high quality or the after-recording mode, as 2 will be described.
3 Input analog audio signals are coupled to an input 4 terminal lA at substantially the same time as video data is coupled to input terminals lY, 1U and 1V of the recording 6 apparatus shown in FIG. 1. Input terminal 1B of FIG. 3 is 7 adapted to receive analog audio signals at a later time, that is, 8 after the original video and audio data are recorded. Stated 9 otherwise, input terminal 1B is adapted to receive audio signals far after recording.
11 Audio processor 15 is comprised of a high quality 12 processing section A which, in the embodiment shown in FIG, 3, is 13 comprised of an analog-to-digital (A/D) converter 34, a 14 compressor 35, an expander 37, a digital-to-analog (D/A) converter 36, a difference circuit 61, an A/D converter 40 and a 16 compressor 41. The audio processor 15 also includes parity 17 circuits 38 and 44, ID/sync circuits 39 and 45 and a multiplexes 18 46. Input terminal 1A is coupled to A/D converter 34 which 19 functions to digitize the input analog audio signals supplied thereto. In one example, this audio signal is a two-channel 21 audio signal. As mentioned above, the analog audio signal is 22 sampled at a sampling rate of 48 KHz. In the present invention, 23 each sample is represented by sixteen bits; and A/D converter 34 24 is adapted to operate at 1.536 MB/sec. to digitize two channels ~0'~~.~~~
PATENT

1 of audio signals supplied thereto by way of input terminal lA (48 2 KHz x 16 bits x 2 channels = 1.536 MB/sec.).
3 Compressor 35 is coupled to A/D converter 34 and is 4 adapted to reduce the frequency of the digitized audio signals by half. Thus, compressor 35 operates as a band compression circuit 6 to convert the data rate of the digitized audio information from 7 1.536 MB/sec. to 768 KB/sec. The compressed audio data is fed 8 back to expander 37, to be described, and also is coupled to 9 parity circuit 38. The parity circuit functions in conventional manner to generate parity bits and adds an error correction 11 parity code to the compressed digitized audio data supplied from 12 compressor 35. This audio data with an appended error correction 13 parity code is coupled to ID/sync circuit 39 which generates 14 identification data to identify the particular audio sector in which this audio data is recorded and also generates 16 synchronizing data which is useful during a reproducing operation 17 to detect the audio data. For example, the sector ID and sync 18 data may be included in the preamble area that precedes audio 19 sector 1, shown in FIG. 2. In this example, it will be appreciated that the sector ID data functions to identify the 21 audio sector as "sector 1".
22 As mentioned above, the compressed audio data produced 23 by compressor 35 is fed back to expander 37 which functions to 24 return the compressed audio data ta-its original data rate of 1.536 MB/sec. The output of expander 37 is coupled to D/A

~~'~:~ ~9 PATENT

1 converter 36 which re-converts the digitized audio data to analog 2 form. The reconverted analog audio signals are coupled to 3 difference circuit 61 whereat they are compared with the original 4 input analog audio signals supplied to terminal lA. Although not shown, it will be appreciated that terminal lA may be coupled to 6 difference circuit 61 by way of a delay circuit which functions 7 to compensate for delays inherent in A/D converter 34, compressor 8 35, expander 37 and D/A converter 36. The difference circuit is 9 adapted to determine differences which may be expected between the original input analog audio signal and the analog audio 11 signal that has been reconverted from its digitized and 12 compressed form. Such differences are referred to herein as an 13 error, and this error, which appears at the output of difference 14 circuit 61, is coupled to yet another compressor 41 by way of an A/D converter 40. The combination of A/D converter 40 and 16 compressor 41 functions to digitize and compress the error that 17 may be present in the originally compressed audio data produced 18 by compressor 35. Stated otherwise, the compressed error 19 provided by compressor 41 comprises compressed audio data that is derived from the original, compressed audio data produced by 21 compressor 35 and that had been supplied at substantially the 22 same time as the video data supplied to input terminals 1Y, lU
23 and 1V of the recording apparatus shown in FIG. 1.
24 The output of compressor 41 is coupled to a terminal a of selector switch 47. As mentioned above, this selector switch 20~~~9~
PATENT

1 operates to select a first or second audio signal recording mode, 2 these modes being described herein as the high quality and after 3 recording modes. When the high quality recording mode is 4 selected, switch 47 engages its terminal a, thereby coupling compressor 41 to a parity circuit 44. This parity circuit is 6 substantially similar to aforedescribed parity circuit 38 and is 7 adapted to generate parity bits which may be added to the 8 compressed error signal produced by compressor 41 as an error 9 correction parity code. The compressed audio error data with this added error correction parity code is coupled to ID/sync 11 circuit 45 which is similar to ID/sync circuit 39 and is adapted 12 to generate sector identification data which identifies audio 13 sector 2. In addition, a sync signal is generated by this 14 ID/sync circuit for use during a reproducing operation to detect and recover the audio data recorded in audio sector 2. As will 16 also be described, ID/sync circuit 45 also generates mode 17 identifying data, such as high quality or after-recording ID
18 data.
19 Multiplexer 46 is coupled to ID/sync circuits 39 and 45 to select either the compressed audio data supplied from 21 compressor 35 (together with the error correction parity code and 22 ID and sync data added thereto) or the compressed error data 23 produced by compressor 41 (together with the error correction 24 parity code and ID and sync data added thereto) for recording either in audio sector 1 or in audio sector 2 as heads 13A and 20~1~9~
PATENT

1 13B scan successive tracks across the record medium. As shown in 2 FIG. 3, the output of multiplexer 46 is coupled to mixer 14 3 whereat the compressed audio signals processed by audio processor 4 15 are combined with digital video signals, as produced by the recording apparatus discussed above in conjunction with FIG. 1.
6 Selector switch 47 also may selectively engage its 7 terminal b to receive compressed audio data for recording in the 8 after-recording mode. As shown in FIG. 3, terminal 1B, which is 9 adapted to receive such after-recording audio signals, is coupled to A/D converter 42 which, like A/D converter 34 operates at 11 1.536 MB/sec. to digitize two-channel analog audio signals 12 supplied thereto. The digitized audio signals are coupled to 13 compressor 43 which, like compressor 35, operates to reduce the 14 data rate of the digitized audio signals, thus reducing the bandwidth thereof. Compressor 43 is coupled to terminal b to 16 supply compressed, digitized audio data at the data rate of 768 17 KB/sec. It will be seen that, when audio processor 15 operates 18 in its after-recording mode, selector switch 47 couples the 19 digitized, compressed, after-recording audio data to multiplexer 46 by way of parity circuit 44 and ID/sync circuit 45 in place of 21 the compressed audio error data that otherwise is coupled to the 22 multiplexes during a high quality recording mode.
23 As mentioned above, ID/sync circuit 45 adds 24 identification data to the compressed audio data supplied thereto by selector switch 47 to identify the particular audio sector in 2~~~~~~
PATENT

1 which this compressed audio data is recorded. In the example 2 described herein, such sector identification data identifies 3 audio sector 2. In addition, ID/sync circuit 45 adds mode 4 identifying data to the compressed audio data supplied thereto.
In the examples described herein, such mode identifying data 6 serves to identify either the high quality or after-recording 7 modes of operation.
8 In operation, let it be assumed that the high quality 9 recording mode is selected. Accordingly, selector switch 47 couples the cascade connection of A/D converter 40 and compressor 11 41 to multiplexer 46 by way of parity circuit 44 and ID/sync 12 circuit 45. Analog audio signals are supplied to input terminal 13 1A substantially simultaneously with the video signals that are 14 supplied to input terminals 1Y, 1U and 1V of FIG. 1. The analog audio signals are digitized by A/D converter 34 and compressed by 16 compressor 35. This compressed audio data is coupled through 17 parity circuit 38 and ID/sync circuit 39 to multiplexer 46. The 18 ID/sync circuit adds sector identification data to the compressed 19 audio data, thereby identifying audio sector 1 as the sector in which this compressed audio data is recorded. When recording 21 heads 13A, 13B scan the audio signal recording area in each 22 track, this compressed audio data is recorded in audio sector 1.
23 The audio data compressed by compressor 35 is fed back 24 to difference circuit 61 by way of -expander 37 and D/A converter 36. It is appreciated that the D/A converter attempts to convert 2~~~~~~
PATENT

1 the compressed audio data to its original analog form, that is, 2 to the form exhibited by the analog audio signals originally 3 supplied to input terminal lA. However, because of quantizing 4 errors in A/D converter 34 and in D/A converter 36, as well as compression errors inherent in compressor 35, it is expected that 6 the reconverted analog audio signals produced at the output of 7 D/A converter 36 differ from the analog audio signals supplied to 8 input terminal lA. Hence, difference circuit 61 produces an 9 error signal representing this difference; and this audio error signal is digitized by A/D converter 40 and compressed by 11 compressor 41. The compressed error data is supplied to ID/sync 12 circuit 45 by way of parity circuit 44. This ID/sync circuit 13 adds identification data to the compressed error data thereby 14 identifying audio sector 2 as the sector in which this compressed error data is recorded, and further identifying the recording 16 mode exhibited by audio processor 15 as the high quality 17 recording mode. Multiplexer 46 supplies the compressed error 18 data to recording heads 13A and 13B at the time that each head 19 scans that portion of the audio signal recording area assigned to audio sector 2. Thus, in the high quality recording mode, 21 compressed input audio data that is supplied at substantially the 22 same time as the video data is recorded in audio sector 1 and 23 compressed error data derived from this compressed input audio 24 data is recorded in audio sector 2.-PATENT

1 If the illustrated audio processor is operatedin its 2 after-recording ode, audio signals which are suppliedinput m to 3 terminal 1B afterthe video and previously supplied signals audio 4 had been recordednow are recorded in sector 2. It is appreciated that,in the after-recording mode, compressedaudio 6 data already is recorded in audio sector 1; and during the actual 7 after-recording operation, no audio signals are supplied to input 8 terminal lA. In the after-recording mode, selector switch 47 9 couples the cascade connection of A/D converter 42 and compressor 43 to multiplexer 46 by way of parity circuit 44 and ID/sync 11 circuit 45. Hence, in the after-recording mode, the audio 12 signals now supplied to input terminal 1B are digitized and 13 compressed, and then supplied to the multiplexer together with 14 identification data which identifies the recording mode as the after-recording mode and also identifies the particular audio 16 sector (that is, audio sector 2) in which this compressed audio 17 data is recorded. It is appreciated that, in the after-recording 18 mode, the audio data supplied to input terminal 1B and recorded 19 in compressed form in audio sector 2 is independent audio data, that is, it is independent of the audio information originally 21 recorded in audio sectors 1 and 2.
22 Turning now to FIG. 4, there is illustrated a block 23 diagram of apparatus adapted to reproduce the video and audio 24 data recorded on a record medium by~the apparatus shown in FIG.
1. To be consistent with the examples discussed above, it is PATENT

1 assumed that the video and audio data are recorded in digital 2 form on magnetic tape in the format shown in FIG. 2. It is . 3 further assumed that recording heads 13A and 13B are used to 4 reproduce the digital and audio data from successive record tracks on the tape, and are referred to as read heads.
6 As shown, the reproducing apparatus of FIG. 4 is 7 comprised of a channel decoder 22, a time base corrector 23, a 8 block decoder 26, a distributor 27, inverse blocking circuits 28 9 and 29, and interpolators 30 and 32. Channel decoder 22 is adapted to decode the digital signals recorded in the form 11 encoded by channel encoder 11. Accordingly, channel decoder 22 12 is compatible with channel encoder 11 and functions to recover 13 the particular encoded format that was used for recording, such 14 as 1,7 code, MFM code, NRZI, etc. The input of channel decoder 22 is coupled to read heads 13A and 13B by amplifiers 21A and 16 218, respectively, and the output of the channel decoder is 17 coupled to time base corrector 23.
18 The time base corrector is conventional and is adapted 19 to remove fitter and other time base errors that may be present in the reproduced digital data. The output of the time base 21 corrector is coupled to a deframing circuit 25 by way of an error 22 checking and correction (ECC) circuit 24. The ECC circuit is 23 adapted to correct errors that may be caused by minor defects in 24 the record medium or that may be produced during the recording and/or reproducing operations. ECC circuitry and the operation PATENT

1 of such circuits are known to those of ordinary skill in the art.
2 If an error is not correctable by the ECC circuit, an error flag 3 is set and further error correction is made by way of 4 interpolators 30 and 32, as will be described.
Deframing circuit 25 is compatible with composing 6 circuit 7 (FIG. 1) and is adapted to carry out an inverse 7 operation. It will be appreciated that the deframing circuit 8 thus converts the recovered bit rate, or data clock, from the 9 frequency normally used for recording to a frequency used for video processing. In addition, the frame structure that had been 11 used by framing circuit 9 to record the video data is reconverted 12 back to block format. This block-formatted video data is coupled 13 from deframing circuit 25 to block decoder 26 which is compatible 14 with data compressor 8 and carries out an inverse operation. For example, if the data compressor functions to compress video data 16 by means of discrete cosine transform, block decoder 26 17 implements an inverse discrete cosine transform operation.
18 Similarly, if the data compressor carried out an adaptive dynamic 19 range coding operation, the block decoder implements an adaptive dynamic range decoding operation. It will be appreciated that 21 the decoded output of block decoder 26 is substantially similar 22 to the input of data compressor 8.
23 Distributor 27 is coupled to block decoder 26 and 24 distributes the decoded video data -into a luminance channel Y and color difference channels U and V. The luminance channel is ~0~~~~5 PATENT

1 coupled from distributor 27 to inverse blocking circuit 28 which 2 functions to recover raster scan data :from the image blocks that 3 had been produced by image block converters 5 and 6 in the 4 recording apparatus. Thus, block sequence data is decoded into a raster scanning sequence of data. It will be appreciated that 6 inverse blocking circuit 28 thus recovers a raster scanning 7 sequence of luminance data and inverse blocking circuit 29 8 recovers a raster scanning sequence of color difference data U
9 and V.
Inverse blocking circuit 29 is coupled to distributor 11 31 which distributes the line sequential color difference signal 12 data U and V to separate outputs which, in turn, are coupled to 13 interpolator 32. Thus, interpolator 32 receives line sequential 14 color difference data U and V and operates to correct errors therein that were not correctable by ECC circuit 24 and also 16 operates to provide those raster lines of color difference data 17 that had not been recorded. It is recalled that, in line 18 sequential format, one line of color difference data U is 19 followed by another line of color difference data V. Thus, alternate lines of color difference data are recorded in the line 2i sequential format. Interpolator 32 supplies to output terminals 22 33U and 33V the original color difference data in successive 23 lines. In addition, whereas line sequencer 4 had reduced the 24 sampling rate of the color difference data signals to 1/2 the original data rate, interpolator 32 recovers the original PATENT

1 sampling rate by multiplying the data rate of the color 2 difference data signals U and v by the factor 2. Thus, color 3 difference data samples are supplied to output terminals 33U and 4 33V at a sampling rate substantially equal to the original sampling rate of the color difference data signals U and V
6 produced by information extractor 2.
7 Inverse blocking circuit 28 is coupled to interpolator 8 30 which operates to correct errors that were not correctable by 9 ECC circuit 24. In addition, whereas frequency converter 3 of the recording apparatus shown in FIG. 1 reduced the sampling rate 11 of luminance data signals Y to a sampling rate of 3/4 their 12 original rate, interpolator 30 recovers the original sampling 13 rate by multiplying the data rate of the luminance signal data Y
14 by the factor 4/3. Hence, interpolator 30 supplies to output terminal 33Y a digital luminance data signal whose clock rate is 16 substantially the same as the clock rate of the digital luminance 17 signal data Y produced by information extractor 2.
18 Channel decoder 22 also is coupled to an audio 19 processor 62 which operates in either the high quality or after-recording mode to recover the original audio information that had 21 been recorded in audio sectors 1 and 2 by the apparatus shown in 22 FIG. 3. The recovered audio signals are supplied to output 23 terminals 33A and 33B.
24 The video signal reproducing apparatus shown in FIG. 4 is known to those of ordinary skill in the art. Audio processor o ~ ~ ~ ~ ~ PATErrT

1 62 is shown in greater detail in FIG. 5 and now will be 2 described. The audio processor includes a time base corrector 3 48, an ID detector 63 and a processing circuit generally 4 identified by the reference numeral B. Processing circuit B
includes expanders 50, 51 and 52, interpolators 53, 54 and 55, 6 digital-to-analog (D/A) converters 56, 57 and 58, a summing 7 circuit 64 and a selector switch 59. Time base corrector 48 is 8 coupled to channel decoder 22 to receive the decoded digital 9 signals that had been encoded in the recording format determined l0 by channel encoder 11. This time base corrector may be similar 11 to time base corrector 23 (FIG. 4) and is adapted to remove 12 fitter and other time base errors that may be present in the 13 decoded audio signals. Time base corrector 48 is coupled to ID
14 detector 63 and also to an error checking and correction (ECC) circuit 49.
16 The ID detector functions to detect the mode 17 identifying data that had been added to the compressed audio data 18 by ID/sync circuit 45 during a recording operation. Accordingly, 19 ID detector 63 detects if the audio data is recorded in a high quality or after-recording mode of operation. As will be 21 described, the ID detector controls selector switch 59 and also 22 switch 60 as a function of the detected mode identifying data.
23 ECC circuit 49 is adapted to detect and correct errors 24 in the compressed, digitized audio-data that is reproduced from the record medium. The ECC circuit is conventional and, as is 2~~~~9~
PATENT

1 known by those of ordinary skill in the art, is adapted to set 2 error flags in the recovered audio data if such data contains 3 uncorrectable errors. As will be described, such errors 4 nevertheless may be corrected or compensated by interpolators 53, 54 and 55. The output of ECC circuit 49 is coupled in common to 6 expanders 50, 51 and 52.
7 It is recalled that the data rate of the digitized 8 audio data is compressed for recording to a rate of 768 EB/sec.
9 Expanders 50, 51 and 52 are adapted to return the data rate of this audio data to the original data rate of 1.536 MB/sec. Thus, 11 the expanders function to multiply the data rate by a factor of 12 two. Each expander is coupled to a respective interpolator 53, 13 54 and 55 which operates to carry out a conventional 14 interpolating operation to correct or compensate for digitized audio data samples that were not correctable by ECC circuit 49.
16 Thus, error compensation is carried out f or those data samples 17 whose error flags have been set.
18 The outputs of interpolators 53, 54 and 55 are coupled 19 to D/A converters 56, 57 and 58, respectively. Each D/A
converter serves to return the digitized audio data samples 21 supplied thereto to analog form. The analog signals produced by 22 D/A converters 56 and 57 are supplied to summing circuit 64 whose 23 output is connected to a terminal a of selector switch 59. As 24 illustrated, the output of D/A converter 56 is connected to terminal b of this selector switch. Selector switch 59 functions 2fl'~~.~~~
PATENT

1 to couple to output terminal 33A either the summed analog audio 2 signals produced by summing circuit 64 or the analog audio signal 3 produced by D/A converter 56. D/A converter 58 is selectively 4 coupled to output terminal 33B by switch 60.
The manner in which audio processor 62 operates now 6 will be described. Let it be assumed that signals recorded in 7 the form shown in FIG. 2 are reproduced from the record medium.
8 Let it be further assumed that the audio signals were recorded in 9 the high quality mode. Accordingly, and as discussed above, the mode identifying data recovered from audio sector 2 is detected 11 by ID detector 63 as the high quality mode. Accordingly, TD
12 detector 63 operates selector switch 69 to connect its terminal a 13 to output terminal 33A and to open, or inhibit, switch 60.
14 The compressed, digitized audio data recovered from audio sectors 1 and 2 are time base corrected by time base 16 corrector 48, subjected to error correction by ECC circuit 49 and 17 supplied to expanders 50, 51 and 52. Since the output of 18 expander 52 is coupled by way of interpolator 55 and D/A
19 converter 58 to switch 60, and since this switch now is opened when audio data that had been recorded in the high quality mode 21 is reproduced, the operation of expander 52 is not relevant to 22 the present discussion.
23 Expanders 50 and 51 expand the compressed data rate of 24 the digitized audio data recovered from audio sectors 1 and 2 from 768 KB/sec. to 1.536 MB/sec. Interpolators 53 and 54 ~0~~~~~
PATENT

1 compensate for errors in the audio data that were not correctable 2 by ECC circuit 49, thus supplying error-corrected/compensated 3 audio data recovered from audio sectors 1 and 2 to D/A converters 4 56 and 57. The outputs from these D/A converters are summed in summing circuit 64. Although not shown in FIG. 5, it will be 6 appreciated that a delay circuit may be used to couple the analog 7 audio signal from D/A converter 56 to summing circuit 64 with a 8 delay substantially equal to the time needed to scan audio sector 9 1 during a playback operation. This delay results in the concurrent supply of the analog audio signals recovered from 11 audio sectors 1 and 2.
12 When the embodiment shown in FIG. 3 is used for a high 13 quality recording mode of operation, it is seen that the audio 14 data recorded in audio sector 2 represents the difference, or error, between the compressed audio data that is recorded in 16 audio sector 1 and the original audio data. During a reproducing 17 operation, the analog audio signal supplied by expander 50, 18 interpolator 53 and D/A converter 56 to summing circuit 64 19 corresponds to the compressed audio data that had been recorded in audio sector 1 and the analog audio signal supplied to this 21 summing circuit by expander 51, interpolator 54 and D/A converter 22 57 corresponds to the aforementioned difference, or error. This 23 difference or error is summed with the audio signal recovered 24 from audio sector 1, thus correcting or compensating for quantizing errors and compression errors that may be present in 20~1~95 PATENT

1 the audio data recorded in audio sector 1. Hence, the output of 2 summing circuit 64 is a high quality audio signal that is 3 remarkably similar to the original input audio signal supplied to 4 terminal lA of the audio processor shown in FIG. 3. This recovered, high quality audio signal is coupled to output 6 terminal 33A.
7 Now, let it be assumed that the compressed audio data 8 recovered from audio sectors 1 and 2 had been recorded in the 9 after-recording mode. Accordingly, ID detector 63 detects this mode identifying data and controls selector switch 59 to couple 11 its terminal b to output terminal 33A and, moreover, closes, or 12 activates, switch 60. Although not shown, it will be understood 13 that, if desired, switch 60 is closed at a delayed time following 14 the scanning of audio sector 1, that is, at the beginning of the scanning of audio sector 2. As will also be appreciated, an 16 additional delay circuit may be coupled to the input of expander 17 50 to provide a delay equal to the time needed to scan audio 18 sector 1 so that the audio signal recovered from audio sector 1 19 is supplied to output terminal 33A at the same time that the audio signal recovered from audio sector 2 is supplied to the il output terminal 338.
22 As before, when compressed, digitized audio data is 23 recovered from audio sector 1, its data rate is expanded by 24 expander 50 from 768 KB/sec. to 1.536 MB/sec., and errors that were not correctable by ECC circuit 49 are compensated by ~0~~~9~
PATENT

1 interpolator 53. The error-corrected/compensated audio data thus 2 recovered from audio sector 1 is converted to analog form by D/A
3 converter 56 and coupled by way of selector switch 59 to output 4 terminal 33A. If desired, when operating in the after-recording mode, a suitable blocking circuit may be activated to block the 6 output from selector switch 59 after the audio data reproduced 7 from audio sector 1 is recovered.
8 When audio data is reproduced from audio sector 2, its 9 data rate is expanded from 768 KB/sec. to 1.538 MB/sec. by expander 52; and errors included therein that were not 11 correctable by ECC circuit 49 are compensated by interpolator 55.
12 The error-corrected/compensated audio data is converted to analog 13 form by D/A converter 58; and when switch 60 is closed, this 14 analog audio signal recovered from audio sector 2 is coupled to output terminal 33B.
16 Thus, in the after-recording mode, analog information, 17 such as a two-channel audio signal that had been recorded in 18 audio sector 1, is reproduced at output terminal 33A, while a 19 different two-channel audio signal that had been recorded in the after-recording mode in audio sector 2 is provided at output 21 terminal 33B.
22 Turning now to FIG. 6, there is illustrated another 23 embodiment of high quality processing section A included in audio 24 processor 15 of FIG. 3. This alternative embodiment is identified by reference numeral A'. In this alternative PATENT

1 embodiment, a single A/D converter 34 is provided, the output of 2 which is coupled to compressor 35 and also to a compressor 41'.
3 The output of compressor 35 is coupled to expander 37, as in the 4 FIG. 3 embodiment, but here, the output of expander 37 is coupled to compressor 41'. Compressor 35 and expander 37 may be 6 substantially the same as shown in FIG. 3, and compressor 41' 7 includes a digital difference circuit, or subtractor, by which 8 the difference between the digitized audio signal produced by A/D
9 converter 34 and the output of expander 37 is obtained. It is this difference which is compressed by compressor 41'.
11 As before, A/D converter 34 digitizes the audio signals 12 supplied thereto to produce digitized audio data at the data rate 13 of. 1.536 MB/sec. Compressor 35 reduces the data rate by one-14 half, thus supplying compressed audio data at a 768 KB/sec. data rate to parity circuit 38. It is appreciated that the output of 16 the parity circuit is recorded in audio sector 1.
17 Expander 37 returns the compressed audio data produced 18 by compressor 35 to the original digitized data rate of 1.536 19 MB/sec. It is appreciated that the digitized audio data provided by this expander exhibits quantizing and compression errors.
21 Accordingly, the difference circuit included in compressor 41' 22 senses these errors by comparing the expanded digitized audio 23 data from expander 37 to the digitized audio data supplied by A/D
24 converter 34. To provide proper tinning, a delay may be imparted 20~~~~~
PATENT

1 to the digitized audio data supplied to compressor 41' by A/D
2 converter 34.
3 Compressor 41' compresses the error between the 4 expanded audio data from expander 37 and the digitized audio data from A/D converter 34 by reducing the data rate by one half.
6 Hence, compressor 41' supplies to terminal a of selector switch 7 47 compressed error data at the 768 KB/sec. data rate. This 8 compressed error data is coupled to parity circuit 44 and 9 subsequently recorded in audio sector 2. Thus, 'the embodiment l0 shown in FIG. 6 achieves substantially the same result as the 11 embodiment shown in FIG. 3, but is implemented by a simpler 12 circuit arrangement.
13 Turning now to FIG. 7, there is illustrated an 14 alternative embodiment of the processing circuit B shown in FIG.
5, this alternative embodiment being particularly useful with the 16 FIG. 6 embodiment of high quality processing section A'. As in 17 the FIG. 5 embodiment, a selector switch 59 is controlled by ID
18 detector 63 to engage its terminal a or terminal b. Here, 19 however, selector switch 59 is coupled to interpolator 53.
Terminal a is connected to the output of expander 51' and 21 terminal b is connected to the output of expander 50. It will be 22 appreciated that expander 50 in FIG. 7 is substantially the same 23 as expander 50 in FIG. 5; and expander 51' in FIG. 7 comprises a 24 modified version of expander 51 in ~'IG. 5. Processing circuit B' also includes expander 52, interpolator 55, D/A converter 58 and PATENT

1 switch 60, all connected in cascade and all being similar to 2 these same components discussed above in conjunction with FIG. 5.
3 Expander 51' is modified to the extent that it includes 4 delay and summing circuits for delaying the digitized audio data recovered from audio sector 1 such that this delayed audio data 6 is present substantially concurrently with the digitized audio 7 data recovered from audio sector 2. It is appreciated that this 8 delay can be triggered by sensing the audio sector 1 identifying 9 data that is recorded with the compressed audio data.
When high quality identifying data is detected by ID
11 detector 63, selector switch 59 connects terminal a to 12 interpolator 53, thereby coupling the output of expander 51' to 13 output terminal 33A. Now, when the digitized, compressed audio 14 data is reproduced from audio sector 1, it is supplied to expander 51' whereat it is combined, or added, with the digitized 16 audio data that is reproduced from audio sector 2. The 17 aforementioned delay included in expander 51' provides proper 18 timing between the audio data recovered from audio sectors 1 and 19 2.
After combining the audio data recovered from audio 21 sectors 1 2, the data rate of the combined audio data and is 22 expanded from 768 KB/sec. to the original data rate of 1.536 23 MB/sec. This expanded audio data is coupled to interpolator 24 whereat errorsthat were not correctable by ECC circuit 49 are compensa ted. The resultant error-corrected/compensated audio 2~~1a9~
PATENT

1 data is converted to analog form by D/A converter 56 and supplied 2 to output terminal 33A. Thus, when the processor is used to 3 recover audio data that had been recorded in the high quality 4 mode, the audio signals provided at output terminal 33A of processing circuit B' are substantially the same as the high 6 quality audio signals coupled to output terminal 33A of 7 processing circuit B (shown in FIG. 5).
8 It will be appreciated that if ID detector 63 detects 9 the after-recording mode identifying data in the signals reproduced from the record medium by read heads 13A and 13B, 11 selector switch 59 engages its terminal b and switch 60 is 12 closed. Accordingly, audio data recovered from audio sector 1 is 13 expanded from its data rate of 768 KB/sec. to its original data 14 rate of 1.536 MB/sec. by expander 50, and this expanded audio data is interpolated by interpolator 53, converted to analog form 16 by D/A converter 56 and supplied to output terminal 33A.
17 Likewise, audio data that is recovered from audio sector 2 is 18 expanded from its data rate of 768 KB/sec. to its original data 19 rate of 1.536 MB/sec. by expander 52; and this expanded audio data is interpolated by interpolator 55, converted to analog form 21 by D/A converter 58 and coupled by switch 60 to output terminal 22 33B. Thus, it is seen that the two-channel audio information 23 that had been supplied for recording at the same time as the 24 video information is provided at output terminal 33A, and after-20~1~95 PATENT

1 recorded two-channel audio information is provided at output 2 terminal 33B.
It is recalled that, in addition to recording mode 4 identifying data, sector identification data also is recorded in, for example, the preamble of each of audio sectors 1 and 2. If 6 desired, expanders 50 and 52 may include sector ID detectors 7 which are adapted to enable the respective expanders upon 8 detecting the corresponding sector identification. Thus, when 9 audio sector 1 is scanned during a reproducing operation, sector 1 ID data enables expander 50 to expand the audio data recovered 11 from audio sector 1 and sector 2 ID data enables expander 52 to 12 expand the audio data recovered from audio sector 2. In 13 addition, and if further desired, the inherent delay in scanning 14 audio sector 2 after audio sector 1 is scanned may be compensated by providing a compensating delay circuit in expander 50.
16 Yet another embodiment of high quality processing 17 section A of audio processor 15 is illustrated as section A" in 18 FIG. 8. It is seen that this embodiment of high quality 19 processing section A" admits of a relatively simple construction including A/D converter 34 whose output is coupled to a 21 compressor 35'. Compressor 35' may be similar to aforedescribed 22 35 (shown in FIG. 3) and includes two outputs, one coupled to 23 parity circuit 38 and the other coupled by way of selector switch ?4 47 to parity circuit 44. _ 2~~~a~~
PATEMT

1 Compressor 35' is adapted to compress the data rate of 2 those digitized audio signals which are supplied for recording at 3 the same time as the video signals. As before, this data rate is 4 reduced from 1.536 MB/sec. to 768 KB/sec. The compressor produces substantially identical compressed audio data at its 6 outputs, thereby supplying redundant audio data to parity circuit 7 38 and, by way of terminal a of selector switch 47, to parity 8 circuit 44. The output of parity circuit 38, after having sector 9 ID and block sync signals added thereto, is recorded in audio sector 1; and the output of parity circuit 44 is recorded in 11 audio sector 2. Since redundant audio data is recorded in audio 12 sectors 1 and 2, errors that may be present in the audio data 13 recovered from one sector, as may be caused by dropout, are 14 compensated by switching to the redundant audio data that is recovered from the other sector. This will be described in 16 greater detail below.
17 It will be appreciated that, when the apparatus shown 18 in FIG. 8 operates in its after-recording mode, selector switch 19 47 is coupled to terminal b such that audio signals which are supplied to input terminal 1B are digitized, compressed by 21 compressor 43 and coupled by way of the selector switch and 22 parity circuit 44, ID/sync circuit 45, multiplexer 46 and mixer 23 14 to be recorded in audio sector 2. Thus, as was the case with 24 the embodiment shown in FIG. 3, after-recorded audio data is compressed and recorded in audio sector 2.

~~'~1~9~
PATENT

1 An embodiment of processing circuit B" that is 2 compatible with high quality processing section A" and is adapted 3 to recover audio data that had been recorded in the high quality 4 or after-recording modes is illustrated in FIG. 9. As shown, the output of ECC circuit 49 is connected in common to expanders 50, 6 51 and 52, and the output of each of these expanders is connected 7 to a respective terminal a, b and c of a selector switch 59".
8 This selector switch is controlled by a switch controller 65 9 having inputs coupled to ID detector 63 and ECC circuit 49, respectively. The output of selector switch 59" is coupled to 11 D/A converter 56 by way of interpolator 53; and the output of 12 expander 52 is coupled to D/A converter 58 by way of interpolator 13 55. As in the FIG. 5 embodiment, D/A converters 56 and 58 are 14 connected to output terminals 33A and 33B, respectively.
In operation, let it be assumed that ID detector 63 16 detects mode identifying data representing the high quality mode.
17 The ID detector thus controls switch controller 65 to connect 18 selector switch 59" to its terminal a. When audio sector 1 is 19 scanned, the compressed audio data recorded therein is reproduced, error-corrected by ECC circuit 49 and expanded by 21 expander 50 from its recorded data rate of 768 KB/sec. to its 22 original data rate of 1.536 MB/sec. The audio data of restored 23 data rate is interpolated by interpolator 53, converted to analog 24 farm by D/A converter 56 and supplied to output terminal 33A.

20~~~9~
PATENT

1 In the event that the audio data recovered from audio 2 sector 1 includes an error that cannot be corrected by ECC
3 circuit 49, an error indication is supplied from the ECC circuit 4 to switch controller 65. In response thereto, the switch controller connects selector switch 59" to its terminal c, 6 thereby coupling expander 52 to interpolator 53. It is recalled 7 that expander 52 operates to expand the data rate of the 8 compressed audio data that is recovered from audio sector 2. For 9 example, and as mentioned above, expander 52 may include a sector ID detector for detecting the sector identification data that is 11 recorded in, for example, the preamble of the audio sectors.
12 When sector 2 identification data is detected, expander 52 13 operates to expand the data rate of the reproduced audio data 14 from 768 KB/sec. to 1.536 MB/sec. Thus, when errors such as drop-out errors are present in the audio data reproduced from 16 audio sector 1, selector switch 59" couples the redundant audio 17 data reproduced from audio sector 2 to interpolator 53, D/A
18 converter 56 and output terminal 33A. Hence, high quality audio 19 reproduction is assured.
It will be recognized that, if desired, a delay circuit 21 may be included in expander 50, or may be connected at the input 22 thereof, to provide proper timing synchronization between the 23 audio data reproduced from audio sector 1 and the audio data 24 reproduced from audio sector 2. Since the audio data recorded in these audio sectors is redundant, a change over of selector 20~1~~~
PATENT

1 switch 59" from terminal a to terminal c does not result in any 2 loss of information. Errors that otherwise would prevent the 3 reproduced audio data from being recovered accurately thus are 4 compensated by changing over the particular expander whose output is coupled to output terminal 33A.
6 If, while recovering audio data from audio sector 2 an 7 error is present therein which cannot be corrected by ECC circuit 8 49, a suitable error indication is supplied therefrom to switch 9 controller 65 which now changes over selector switch 59" to its terminal b. Accordingly, expander 51 is coupled by selector 11 switch 59" to output terminal 33A via interpolator 53 and D/A
12 converter 56 and audio data recovered from audio sector 1 thus is 13 supplied as analog audio signals to output terminal 33A. Hence, 14 if an error is present in the audio data reproduced from sector 2, that audio data is replaced by the redundant audio data 16 reproduced from audio sector 1 so as to assure the high quality 17 reproduction of audio information.
18 Expander 51 may include a sector ID detector which, 19 upon detecting audio sector 1 identification data, enables the operation of the expander. In addition, a delay circuit may be 21 provided at, for example, the input to expander 51 so as to 22 compensate for inherent delays between the audio data that is 23 reproduced from audio sector 1 and the audio data that is 24 reproduced from audio sector 2. By-compensating for such delays, the outputs of expanders 51 and 52 are substantially identical at ~0~~~~~
PATENT

1 any given period of time. Thus, an error that may be present in 2 audio data recovered from one sector is compensated by 3 substituting the same audio data that is recovered from the other 4 sector.
When ID detector 63 detects the mode identifying data 6 representing the after-recording mode, switch controller 65 7 connects selector switch 59" to, for example, terminal a. Thus, 8 the audio data which is reproduced from audio sector 1 is 9 expanded by expander 50 and coupled through the selector switch to output terminal 33A by way of interpolator 53 and D/A
11 converter 56. Also, audio data that is reproduced from audio 12 sector 2 is expanded by expander 52 and coupled to output 13 terminal 33B by way of interpolator 55 and D/A converter 58.
14 Hence, the after-recorded audio data that had been recorded in audio sector 2 is provided at output terminal 33B, as was the 16 case for the embodiments discussed above in connection with FTGS.
17 5 and 7.
18 It will be recognized that, although switch controller 19 65 connects selector switch 59" to its terminal a for the recovery of audio data from audio sector 1 in the after-recording 21 mode, substantially the same result is achieved if the selector 22 switch is connected to its terminal b.
23 In the embodiments described herein, the video and 24 audio data are recorded in a segment of the type shown schematically in FIG. 2. In this FIG. 2 format, audio sector 1 ~0~~~9~
PATENT

1 is separated from the video sector by postamble, margin and 2 preamble areas. An alternative format of a segment that may be 3 recorded by the present invention is illustrated in FIG. 10, 4 wherein audio sector 1 may be thought of as being an extension of the video sector. That is, audio-s~c~'or l simply follows the 6 video sector and is not spaced therefrom by a postamble area, a 7 margin area or a preamble area. By eliminating these non-data 8 areas, the available room for recording useful information, such 9 as video or audio data, is enlarged. Alternatively, if the same l0 amount of video and audio data is recorded in a segment, the 11 overall length of that segment and, thus, the overall length of a 12 track may be reduced. Hence, the recording density of the 13 format shown in FIG. 10 is greater than that of the format shown 14 in FIG. 2.
While the present invention has been particularly shown 16 and described with reference to preferred embodiments, it will be 17 readily appreciated by those of ordinary skill in the art that 18 various changes and modifications may be made without departing 19 from the spirit and scope of the invention. For example, the different recording modes with which the present invention 21 operates need not be limited solely to high quality and after-22 recording modes. Also, although each audio sector has been 23 described as having two-channel audio data recorded therein, it 24 will be appreciated that the audio data may be recorded as single channel data. Still further, it will be recognized that in the PATEN

1 various embodiments of the audio data .reproducing apparatus, 2 selected delays may be used if time coincidence between the audio 3 data recovered from audio sector 1 and audio data recovered from 4 audio sector 2 is desired. Some of these delays have been described above and others will become readily apparent to those 6 of ordinary skill in the art.
7 Therefore, it is intended that the appended claims be 8 interpreted as covering the embodiments specifically disclosed 9 herein, those various modifications and alternatives which have been discussed above, and all equivalents thereto.

Claims

1. A method of recording video and audio data onto video and audio signal recording areas of a track of a record medium, said method including the steps of:
compressing audio data that is supplied at substantially the same time as the video data;
recording said compressed audio data in a first audio sector of said audio signal recording area;
selecting a first or second audio signal recording mode;
selectively providing derived compressed audio data that is derived from the audio data supplied at substantially the same time as the video data when said first audio signal recording mode is selected, and selectively providing independent compressed audio data when said second audio signal recording mode is selected; and recording the provided derived or independent compressed audio data in a second audio sector of said audio signal recording area.

2. The method of Claim 1 wherein said video and audio signal recording areas are included in one of a plurality of recording segments in said track.

3. The method of Claim 1 wherein said step of selectively providing derived compressed audio data comprises determining an error in the compressed audio data that is supplied at substantially the same time as the video data, and compressing said error.

4. The method of Claim 3 wherein said step of determining an error in the compressed audio data comprises digitizing input analog audio data that is supplied at substantially the same time as the video data, compressing the digitized audio data, expanding the compressed, digitized audio data, converting the expanded digitized audio data to analog form, determining a difference between the converted analog audio data and the input analog audio data, and digitizing the determined difference.

5. The method of Claim 3 wherein the step of compressing audio data includes the steps of digitizing input analog audio data and compressing the digitized input audio data;
and wherein said step of determining an error in the compressed audio data comprises expanding the compressed audio data, and determining a difference between the expanded audio data and said digitized input audio data.

6. The method of Claim 1 wherein said step of selectively providing derived compressed audio data comprises supplying the same said compressed audio data for recording in said second audio sector of said audio signal recording area, whereby redundant compressed audio data is recorded in both said first and second audio sectors.

7. The method of Claim 1 wherein said first audio signal recording mode is a high quality recording mode and said second audio signal recording mode is an after-recording mode.

8. The method of Claim 7 wherein said independent compressed audio data is provided for recording at a time subsequent to the recording of said video data.

9. The method of Claim 1 wherein said first audio sector is located adjacent said video signal recording area.

10. The method of Claim 1 further comprising the step of recording a mode identifying signal with said audio data to identify the audio signal recording mode that has been selected.

11. The method of Claim 10 wherein said mode identifying signal is recorded in said second audio sector with said derived or independent compressed audio data.

12. A method of reproducing video and audio data from video and audio signal recording areas of a track of a record medium, said audio data being recorded as compressed audio data in a first audio sector and, depending upon the recording mode used to record the audio data, audio data is selectively recorded in a second audio sector as derived compressed audio data that is derived from the audio data in said first audio sector or as independent compressed audio data, said method comprising the steps of:
scanning said video and audio signal recording areas to recover video and audio data, respectively;

separating the recovered audio data from said video data;
sensing the recording mode that was used to record the audio data;
expanding the compressed audio data recovered from said first and second audio sectors;
combining the expanded audio data recovered from said first and second audio sectors to produce an output audio signal when a first recording mode is sensed; and supplying the expanded audio data recovered from said first and second audio sectors as separate output audio signals when a second recording mode is sensed.

13. The method of Claim 12 wherein a recording mode identifying signal is recorded in at least one of said first and second audio sectors, and said step of sensing the recording mode comprises reproducing said identifying signal and detecting the reproduced identifying signal.

14. The method of Claim 12 wherein said derived compressed audio data that is recorded in said second audio sector in a first recording mode comprises compressed error data that is derived from a difference between the compressed audio data that is recorded in said first audio sector and audio data originally supplied for recording; and said step of combining comprises error correcting the expanded audio data recovered from said first and second audio sectors, converting the error-corrected audio data recovered from said first and second audio sectors to analog signal form, and summing the analog audio signals recovered from said first and second audio sectors to produce an output analog audio signal.

15. The method of Claim 12 wherein said derived compressed audio data that is recorded in said second audio sector in a first recording mode comprises compressed error data that is derived from a difference between the compressed audio data that is recorded in said first audio sector and audio data originally supplied for recording; and said step of combining comprises summing the expanded audio data recovered from said first and second audio sectors, error correcting the summed audio data, and converting the error-corrected, summed audio data to analog signal form to produce an output analog audio signal.

16. The method of Claim 12 wherein said derived compressed audio data that is recorded in said second audio sector in a first recording mode comprises the same compressed audio data that is recorded in said first audio sector; and said step of combining comprises selecting the expanded audio data recovered from one of said audio sectors, sensing an error in the selected audio data, and changing over the selection of expanded audio data recovered from one to the other of said audio sectors when an error is sensed.

17. The method of Claim 12 wherein said first recording mode is a high quality recording mode and said second recording mode is an after-recording mode.

18. The method of Claim 17 wherein the independent compressed audio data that is recorded in said second audio sector comprises two-channel audio data independent of the compressed audio data that is recorded in said first audio sector.

19. The method of Claim 17 wherein the compressed audio data that is recorded in said first audio sector comprises two-channel audio data that is recorded at substantially the same time as the video data.

20. The method of Claim 12 wherein said first audio sector is located adjacent said video signal recording area.

21. The method of Claim 12 wherein said video and audio signal recording areas are included in one of a plurality of recording segments in a track.

22. Audio recording apparatus for use in a system which records video and audio data onto video and audio signal recording areas of a track of a record medium, said apparatus comprising:
compressor means for compressing audio data that is supplied for recording at substantially the same time as the video data;

first recording means for recording said compressed audio data in a first audio sector of said audio signal recording area;
mode selecting means for selecting a first or second audio signal recording mode;
audio data selection means for selectively providing derived compressed audio data that is derived from the audio data supplied for recording at substantially the same time as the video data when said first audio signal recording made is selected, and for selectively providing independent compressed audio data when said second audio signal recording mode is selected; and second recording means coupled to said audio data selection means for recording said derived or independent compressed audio data in a second audio sector of said audio signal recording area.

23. The apparatus of Claim 22 wherein said video and audio signal recording areas are included in one of a plurality of recording segments in said track.

24. The apparatus of Claim 22 wherein said audio data selection means comprises error determining means coupled to said compressor means for determining an error in the compressed audio data that is supplied for recording at substantially the same time as the video data, and second compression means for compressing said error.

25. The apparatus of Claim 24 wherein said error determining means comprises A/D means for digitizing input analog audio data that is supplied for recording at substantially the same time as the video data, means for compressing the digitized audio data, means for expanding the compressed, digitized audio data, D/A means for converting the expanded digitized audio data to analog form, difference means for determining a difference between the analog audio data from said D/A means and the input analog audio data, and additional A/D means for digitizing the difference from said difference means.

26. The apparatus of Claim 24 wherein said compression means includes A/D means for digitizing input analog audio data and first compressor means for compressing the digitized audio data; and wherein said error determining means comprises expansion means coupled to said first compressor means for expanding the compressed audio data, and means for determining a difference between the expanded audio data from said expansion means and said digitized audio data from said A/D means.

27. The apparatus of Claim 22 wherein said audio data selection means includes switch means coupled to said compression means for supplying the same said compressed audio data for recording in said second audio sector of said audio signal recording area, whereby redundant compressed audio data is recorded in both said first and second audio sectors.

28. The apparatus of Claim 22 wherein said first audio signal recording mode is a high quality recording mode and said second audio signal recording mode is an after-recording mode.

29. The apparatus of Claim 28 wherein said independent compressed audio data is provided for recording at a time subsequent to the recording of said video data.

30. The apparatus of Claim 22 wherein said first audio sector is located adjacent said video signal recording area.

31. The apparatus of Claim 22 further comprising ID
means for generating a mode identifying signal for recording with said audio data to identify the audio signal recording mode that has been selected.

32. The apparatus of Claim 31 wherein said ID means is coupled to said second recording means for recording in said second audio sector with said derived or independent compressed audio data.

33. Apparatus for reproducing video and audio data from video and audio signal recording areas of a track of a record medium, said audio data having been recorded as compressed audio data in a first audio sector and, depending upon the recording mode that was used to record the audio data, said audio data also having been selectively recorded in a second audio sector as derived compressed audio data that is derived from the audio data in said first audio sector or that is independent compressed audio data, said apparatus comprising:

means for scanning said video and audio signal recording areas to recover video and audio data, respectively;
separating means for separating the recovered audio data from said video data;
mode sense means coupled to receive the recovered audio data for sensing the recording mode that was used to record the audio data;
expanding means coupled to said separating means for expanding the compressed audio data recovered from said first and second audio sectors;
combining means for combining the expanded audio data recovered from said first and second audio sectors to produce an output audio signal when a first recording mode is sensed; and means for supplying the expanded audio data recovered from said first and second audio sectors as separate output audio signals when a second recording mode is sensed.

34. The apparatus of Claim 33 wherein a recording mode identifying signal is recorded in at least one of said first and second audio sectors, and said mode sense means comprises means for detecting the identifying signal in the data recovered from said at least one audio sector.

35. The apparatus of Claim 33 wherein said derived compressed audio data that has been recorded in said second audio sector comprises compressed error data derived from a difference between the compressed audio data that was recorded in said first audio sector and audio data originally supplied for recording;
and said combining means comprises error correcting means for error correcting the audio data expanded by said expanding means, D/A means for converting the error-corrected audio data recovered from said first and second audio sectors to analog signal form, and means for summing the analog audio signals recovered from said first and second audio sectors to produce an output analog audio signal.

36. The apparatus of Claim 33 wherein said derived compressed audio data that has been recorded in said second audio sector comprises compressed error data derived from a difference between the compressed audio data that was recorded in said first audio sector and audio data originally supplied for recording;
and said combining means comprises means for summing the expanded audio data recovered from said first and second audio sectors, error correcting means for error correcting the summed audio data, and D/A means for converting the error-corrected, summed audio data to analog signal form to produce an output analog audio signal.

37. The apparatus of Claim 33 wherein said derived compressed audio data that has been recorded in said second audio sector comprises the same compressed audio data that was recorded in said first audio sector; and said combining means comprises selector means for selecting the expanded audio data recovered from one of said audio sectors, error sense means for sensing an error in the selected audio data, and change-over means for changing over the selection of expanded audio data recovered from one to the other of said audio sectors when an error is sensed.

38. The apparatus of Claim 33 wherein said first recording mode is a high quality recording mode and said second recording mode is an after-recording mode.

39. The apparatus of Claim 38 wherein the independent compressed audio data that was recorded in said second audio sector comprises two-channel audio data independent of the compressed audio data that was recorded in said first audio sector.

40. The apparatus of Claim 38 wherein the compressed audio data that was recorded in said first audio sector comprises two-channel audio data that was recorded at substantially the same time as the video data.

41. The apparatus of Claim 33 wherein said first audio sector is located adjacent said video signal recording area.

42. The apparatus of Claim 33 wherein said video and audio signal recording areas are included in one of a plurality of recording segments in a track.