US 2734100 A
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PECT/F/ER VAR/ABLE T/PANSM/SS/ON FROM TO SUSTA/NED F/PEOUE/VCY AMPLIFIER @Mwmc/ fiaiaif United States, Patent METHOD AND APPARATUS FOR PRODUCING SOUNDS Osmond Kendall, Ottawa, Ontario, Canada Application May 7, 1951, Serial No. 224,927
Claims priority, application Great Britain May 16, 1950 32 Claims. (Cl. 179-1) This invention relates to a method and apparatus for producing sounds which may be auditioned or recorded as desired and is particularly concerned with the produc tion of original recordings of music which may be created directly in sound-track form without prior instrumentation by musicians.
Prior to the present invention, musical expression has been limited by the fixed characteristic tones inherent in a given acoustic musical instrument. It had to be accepted by the composer and the arranger of a piece of music that some musical instruments are inflexible in that they possess a characteristic touch which is determined by their design. This rigid factor is a limitation thwarting the full freedom of music production according to the concepts of a composer or arranger. It has been proposed to overcome this difiiculty, which is inherent in music originated by acoustic instruments, by hand-drawing sound waves and photographing the hand-drawn sound waves to produce a sound track. While direct production of a sound track by hand-drawing creates new musical freedom from the characteristic touch of instruments, it has never been used to any great extent owing to it being painstaking and laborious.
The present invention provides a method and apparatus for producing sounds which provide musical freedom from the characetristic touch of instruments without the painstaking and laborious work of hand-drawing each note.
The present invention takes cognizance of the theory that the quality of a sound, such as a musical note, which makes it recognizable as being originated by a particular musical instrument and even by a particular musician, is a combination of some of the following components of music:
(a) A primary sustained audio frequency which may be a single frequency or may include a series of harmonics. The relative amplitudes of any of these frequencies may vary from zero to one hundred percent of the frequency of highest amplitude in the series, including the fundamental frequency. A number of different fundamental frequencies and their respective series of harmonics may concurrenlty comprise the basic sustained audio frequency.
(b) A shifting in frequency of the basic sustained audio frequency, as exemplified in slide string-instrument renditions, tremolo effects, clang percussive note advents and vibrato die-away eifects, etc.
(0) A progression of varying instant amplitudes which comprise the element of tone in the rendition of a given note of music. Such an envelope of sequential amplitudes does not have separable components which differentiate between touc as provided by the nature and construction of the musical instrument, and touch which is characteristic of expression as played by the musician. The contour of the envelope may be further complicated by acoustic reverberation which also appears in part as a sequence of instant amplitude changes. In the playing of a musical instrument the natural tone is 2,734,100 Patented Feb. 7, 1956 'ice emitted at the selected frequency in a progression of changes of amplitudes as determined by the touch of the musician and by the touch resulting from the construction of the instrument in question. This combined touc may be observed in timbrillated contour form on an oscilloscope.
(d) Duration and advent time expressed as physical lengths which are adjustable in the following sense: for example consider an envelope of the touch of a piano which rises rapidly to a maximum on the impact of the felt and may decay over a duration of six seconds depending on the note selected. The characteristic but contracted contour of the envelope will be similar in the case of a higher frequency note lasting one second. It will be apparent that the required envelope contour is not obtained by cutting off or deleting 5 seconds worth of the 6 second contour length. It will further be apparent that placement of the advent of a note on a given soundtrack is a convenient physical length equivalent of time relationship between notes of music which may be in recording assembly.
According to the present invention an envelope contour, made in accordance with the component of sound corresponding to a progression of instant amplitudes of sound, is used to control the audio frequency current corresponding to the primary audio frequency component of sound so that the residue of the audio frequency current conforms to the envelope contour. The residue of the audio frequency current may then be recorded according to given advent placements on the sound-track of a recording.
In accordance with the present invention the audio frequency current corresponding to the primary audio frequency component of sound forms a musical raw material which is characetristic of any actual or imaginary musical instrument as desired by the composer. The audio frequency current is deleted according to a desired envelope contour which supplies the touch component of music, leaving a residue of the audio frequency current which can be recorded and rerecorded in accordance with deliberated advent times as represented by linear distances along a sound-track.
The present invention enables the producer of music to have a full choice of any characetristic tone and an independent but equally full choice of any characteristic touch, without restriction to the fixed combinations of characteristics obtainable from selected musical instruments. According to the present invention the notes of a musical composition do not have to be produced in,
any particular time sequence of notes, as is the case when music is produced conventionally, and each note may be individually produced and tailored to the composers or the arrangers wishes before being mixed with other notes of the composition.
A further important advantage resulting from the ability to produce notes individually without regard to any particular time sequence of notes is that synchroni- Zation of the music recorded on the sound-track of a motion picture. film with the visual content of the film can be achieved. This synchronization is often desired by the composer and arranger but, prior to the present invention, it was usually not obtainable due to the difficulty of playing live music (that is, music produced acoustically by musicians) in a predetermined synchronized relation to the action recorded in the visual content of the film. When live music is recorded on a soundtrack it may prove completely unusable should even a small portion of it be undesirably executed, mislocated as to precise advent in time, incorrect in pitch relationship, undesirably combined with acoustic reflections, or otherwise improperly performed. Perfection of the final recorded music by subdividing it into editable fragments of recordings of thecomponent music is precluded because musicians a n tiSFWFQIi YrsafOtm he. omp n nts.
of their art in a state of complete dissociation from musical contexts. Also, since the individual instrumcntations of an orchestration are merged into a complex wave in a single medium, either air or the recording channel, it follows that the editing of an offendingcomponent of live music in a given rendition is impractical. Thus, prior to the present invention, it was either necessary to repeat the entire recording or to accept a recording of a standard of performance below that which is possible.
In the present specification and claims the term soundtrack is usedto denote a track on a medium adapted to receive a recordingof sound. The term wide' soundtraclc is used 'to denote a track on a. medium such as magnetic tape, photographic film or the like; adapted to receive a recording invariable signal density form extending acrossa widthadaptedfor convenient manual erasure of portions of .the recordedvolume of .a signal.
The invention will befurther described with reference to the accompanying drawings, in which:
Figure 1, isja perspective view of apparatus in ac cordance with an embodiment of. the invention;
Figure 2 is; schematic diagram of the apparatus shown in Figure 1;
Figure 3 is a schematic diagram of a preferred form of aperiodic polyharmonic generator according to the invention, for use withthe apparatus shown in Figure 2;
Figure4 is a schematic diagram of a phase rotator for use with the apparatus shown in Figure 3;
FigureS is a schematicdiagram of-another form of aperiodic polyharmonicgenerator, according to the'invent'ion, 'for use with theapparatus shown in Figure 2;
"Figure lSis a table oflocal signal sources for outphasing unwanted harmonics which may be generated by the square law amplifiers of thepolyharmonic generator asshown in Figure Figure? is a chart illustrating thevolume percentages of the component frequencies in which is comprised the recognition of the character of a given musical'ins't'rumerit as exemplified by the percentages comprising one note of the oboe;
Figure 8 is a schematic diagram of a dual sound-track magnetic recorder combination, according to the invention;
Figure 9 is a schematic diagram of a repetitious multisound-track magnetic recorder combination, according to the invention;
Figure 1013 a schematic diagram of anothr combinationof signal contouring elements, according to the invention for use with the apparatus shown in Figure 2;and
Figure '11 is a schematic diagram of another combination'o'f signal contouring elements, according to the invention, for use with'the apparatus shown in 'Figure2..
As shown in'Figure 1 apparatus according to the inventioncan be arranged on;ajtable 1fin a convenient manner for use by a jcomp oser 2 located at a conven'ient height for operation ofthe apparatus by the composer seated before it. An audio oscillator 3, a polyharmonic generator 4 and a master switc board 5 are located on a shelf 6 runningacross the ba'clco f the table. 1. Another shelf 7 supports on audi tioningloudsp'eaker 8. located magnetic recording elcments as shown comprised 'l Pjhe&d' 1 t g. ad 0.- esol hea 11. me netic film 12, driving sprocket driving sprockets 14, "'15,;. carrying a film type of synchronoils one sheet 16. Projecting through the .top of the table at a convenient working angle is an oscilloscope 11 fitted with a guide slot 18 for atran slucent sheet 19011 which 'an opaque "envelope-conture lo is. disposed. A fluorescent image 21 of an ultrasonic signal is shown he hind 191' A photocell 22in a hinged light-excluding cover ZIqmay-be pulled downby the knob 24 to, photoelectr'ically pi'clc up the interrupted pulses 'of light caused V The table 1 hasit's op" On the top of the table 1 are 13. coupled to. j'which are by the contour line 20 covering the travelling spot comprising. the, image. 21. may be assembled in recorded form by: Adjusting the audio oscillator 3 to a frequency corresponding to a fun damental of a note in a music score. By injecting the selected frequency into the polyharmonic generator 4, the characteristics of a desired musical instrument may be heard by adjusting the amplitude controls of the specified harmonics 25 which are generated in 4, and auditioning the combined output thereof by speaker 8 as switched on at master control means 5.
A desired rendition of a singlenote is then. prepared by drawing an envelope contour 20 'on 'the 'transparent sheet 19 using forexample a greasepencil. By closing cover 23 the photocell 22 will transmit the contour every time the sweep repetition occursi Th control signal image as modified by the contour 20 is biased ofl however by the single sweep adjustment of the oscilloscope. A push button control at 5 initiates thesweep action forsingle horizontal scan of the contour according to.
the sweep time-constant selected. Each time the auditioning button initiates the oscilloscope sweeping at the selected duration the output from polyharmonic generator 4 will be partly transmitted to the speaker 8 in accordance with the envelope 20 pulses 21 from the oscilloscope 17. By reshaping the attack and decay contours of the envelope 20 musical notes maybe edited as auditioned When a satisfactory note has been produced it may be recorded on magneticfilm 12 as often as it maybe required in the score. By switching to automatic record at master switching control 5, the recording of the note occurring in precise advent placement may be arranged according to convenient cue marks indicated at arrow 26 by prerecording sweep track facility provided for this purpose.
Further notes may be prepared in a similar fashion and'may be recorded onthe same track in staggered'or overlapping. placements as desired by playback of'the recording at 9 and concurrently rerecording at 11 in mixed form with an additional seriesof placements of a new note. At the same time if desired the recording which is picked up at 9 may be erased at 10. In addition'the mixed recording and rerecording facilities by virtue of theftr'ansverse multitrack capacity of the head arrangements 9, 10, and 11 enable concurrent auditioning of notes in" the preparation of chords.
A, block diagram of the apparatus shownin Figure l. is giveninFigure 2. As shown in Figure. 2, the audio oscillator 3 feeds .the polyharmonic generator 4, which willbe described in more detail later. tours which may be based on the fimbrillated outlines of'oscillograms of notes of music are inscribed at 20 on thesheet19. The sheet is disposed to cover the luminous image 21. which is displayed on the cathode ray t ub e 17 and which'is derived from. an ultrasonic oscillator 27 by connection to the horizontal! 28 of the oscilloscope deflection system 30. 'The vertical deflection plate isys tern 31of theo'scilloscope is connected to 32: pulses from a sweep initiating which may be set to record recorder 33 at record head 34. Playback from head 34 may be routed by switch 32 to fire the single sweep system. of the oscilloscope. The switch 32 may further connect oscillator 27 to the head 34 Manual firing'of the single s push. button 35. The time base control of. the single sweep system of the oscilloscope is conventional electronic practice and is not shown in order to reduce schematic congestion. The recording of the single sweep firing signal is advantageously. combined ingof a sweep-duration controlling signal having an amplitude adjusted to provide in playback a biasing volt age for the grid of a tube connected to function as the variable resistance whichdetermines the time constant of the capacitor associated with the oscilloscope swecp:
According to the invention music.
initiating .pulses on a special sound The envelope con for erase purposes.v Veeps may be efiected .by.
with the record i magma system as aforementioned. Thus the advent placement and the time during which a given contour envelope will be extended may be prerecorded. The range of the single sweep is made to be aproximately 0.1 to seconds duration for average musical synthesis.
The preferred electronic arrangement for the pickup of the contours inscribed next to the face of the oscilloscope tube may be replaced by the direct electrostatic sampling of the moving spot by using a conductive material for the contour line as inscribed, the inception of the line being connected to an electronic switch which in turn controls the variable transmission element 37. The use of the photocell (photo multiplier) pickup of the contour as shown in Figure 2 is preferred because more precise contour sampling is facilitated.
The envelope contour may be drawn on the surface of a translucent sheet 19 or the contour may be an opaque cutout, and held in the guide slot 18 between the photocell 22 and the cathode ray tube 28 at location' 29. The signal from photocell 22 may be connected by switch 36 to control the variable transmission element 37 which may be separately controlled by contour signals from 38 by switch 39. A source of audio as picked up by microphone 40 and amplified by 41 may be routed to an envelope demodulator 38 by switch 42. Alternatively switch 42 may route the audio signal to the electronic gain control element 43 which is connected in the input of the polyharmonic generator 4.
The output of the variable transmission element 37 is connected to a volume mixer 44 to which is further connected playback signals from head 9. The mixed pair of signals are connected to the recorder amplifier 45, the output of which may be routed by switch 46 to record at head 11 or the output may be routed by switch 47 to control the variable transmission element 37 with prerecorded contour signals.
A magnetic recording medium is preferred which may be magnetic film 12 conventionally driven in the direction shown by the motor 48 as determined by the forward and reverse type motor control 49.
The erase head 10 is powered from oscillator 27 by switch 50. The switch 51 is independent of 50 and supplies the signal for the control image 21. Switch 52 provides means for rerecording with superposed envelope contours by connecting the audio playback to amplifier 41 through 42 to gain control 43 and a reprocessing operation as described.
All switches as numbered heretofor and additional switching routes (not shown), as will be described or postulated, are located for convenience in the master switchboard 5 (Figures 1 and 2). To avoid overly congesting the diagram, many of the connections to and from the switchboard 5 are not shown, but are located in the direct routes as shown in the diagram.
The auditioning speaker 8 and amplifier 53 may be connected by switch 54 to any signal in the system.
Referring now to Figure 3 which details one form of.
polyharmonic generator 4 as shown in Figures 1 and 2. The preferred generator is an aperiodic type. The usual method of harmonic generation selects, by resonant networks in the output of a non-linear transmission element, those frequencies which comprise 'the desired harmonic. Such a method, however, will only perform part of the desired objectives of this invention as the harmonics selected will require readjustment of the resonant networks involved whenever the fundamental frequency is changed. In the forthcoming disclosures it will be apparent that such manual tuning-in of multiple harmonics which may be shifting is infeasible.
In Figure 3 the wave of the desired fundamental pitch as injected into the electronic gain control 43, is fed to the input of an aperiodic quadrature amplifier 55 of novel design wherein multiple phase shifts produce the output on connection 56 and produce the output on connection 57 each of which differs from the other by a constant phase rotation of approximately degrees over the audio frequency range. It is further understood that the pair of signals which are in quadratureat the:
output bear no fixed phase relationship to the frequency which may comprise the input. She signals on 56 and 57 are injected into phase inverter amplifiers 58 and 59. The four-phase outputs resulting therefrom are quadrature fed to a virtual potentiometric ring or rings as shown enclosed in the circle 60. It will be apparent to those versed in electronics that any desired number of polyphase voltage signal sources may be derived from connections made to the resistors comprising the rings as' schematized. Table 61 which is included in Figure 3, shows the value of each resistance-segment in degrees around the potentiometric ring multiplied by a suitable constant. In the schematic view a three-phase connection is shown, it being understood that any desired number of phases may be connected to the appropriate taps in a similar manner. In the three-phase example the connections feed the rectifier array 62, 63 and 64 which are decoupled from cross-loading effects by resistors 65, 66 and 67. The output 68 in pulsating D. C. is injected into a suitable square law amplifier 69 which is biased to produce the third harmonic wave 70 of the injected input to the electronic gain control 43 by means of nonlinear amplification of the higher order harmonics otherwise produced as dotted in at 71. The volume control 72 feeding the output 73 is decoupled from similar networks and gain controls from each of the other harmonics by means of resistor 74. The actual number of polyphase rectifier networks equals the number of harmonics required of which ten have been found desirable.' A rectifier is required for each frequency which is involved in addition to the fundamental. In the case of a generator producing ten harmonics it is necessary to use a total of 54 rectifiers.
Referring to Figure 4, which is a schematic view detailing one form of the aperiodic quadrature amplifier 55 shown in the circuit of Figure 3, the input signal is fed into two or more staggered phase-shifting amplifiers at 75 I and 76. Each consecutive network 77, 78 and 79 in the cascade shown provides a degree maximum rotation of phase with changing frequency. The phase-shifting constants are chosen to moderately overlap the maximum rotation of a stage with the start of rotation of the next stage at a given frequency. In the case of the three cascaded stages shown a total output rotation of approximately 420 degrees relative to the input may be obtained with a frequency range of 30 cycles to 10 kc. In a similar manner the cascade 80, 81, and 82 is designed to lag the cascade 77, 78, and 79 by a phase angle of 90 degrees over the audio frequency band desired.
Another aperiodic means of generating polyharmonics is schematically drawn in Figure 5 wherein the input from the selected frequency is brought to a constant amplitude by an electronic gain control 83 and is injected into one of two species of square law amplifiers 84 and 85. As is well understood in the electronic arts, the output will contain both the input frequency and its first harmonic at connection 86. The input frequency also feeds a cathode follower output stage 87 whose output is controlled by potentiometer 88 and connected by a decoupling resistor 89 to an output terminal 90 which is common to all harmonics. The output 86 of the square law amplifier is fed to a cathode-coupled stage 91 through a resistor 92. The output 86 contains the amplified input frequency in opposite phase in and it is outphased in resistor 92 by means of a feed in from the cathode of stage 87 through an outphasing feed resistor 93. The remaining frequency 2 n is a desired harmonic and is controlled at cathode-coupled stage 91 by potentiometer 94 for injection into the common output 90.
The two output frequencies fn and 2fn which occur at the cathodes of stages 87 and 91 respectively are de-- 7- square lawsarnplifier 85. As .is well understood in the art, thmoutput produced .by the resulting,- hetrodyne. is .com-.
prised of frequencies fn, 2m, 3131, and 47%.. The. fre-.
quency 3f); is fed to a,3r.d harmonic output stage 97 while the unwanted frequencies fn, 2f anddfnare outphascd through resistor 98, 99;and lilO. The frequency 4 requiredfor outphasing is taken from stage 101 which is derived from the outphased output 162 of stage 1il3;while. the. other frequencies are outphased from thecathodes.
aretabled in Figure 6. It, will beapparent therefrom that outphasing frequencies, as required for .the odd number harmonics, depend on combinations wherein higher-frequency even number, harmonics are concurrently produced.- It will further be apparent that electronic aperiodic harmonic generation, methods are disclosed whereby optional harmonics may be forthcoming whereas the initiating fundamental frequency may be independently controlled orideletcd-a desirable function in the fullsynthesis of sound andmusic.
Referring again to Figure 2, the following is a description of a mode of the operations which may be used in theproduction of music according to the invention:
Theconventional magnetic film 12 is threaded to feed from sprocket reel 13. The record switch 46 is open. Cuesheets are prepared from the desired musical score. Eachmusical note is deliberated and those which have the same pitch and which postulate similar execution from one giyen instrument are transcribed. Notations of timir g advents which may. be derived from tables relating.
sound-track time lengths to conventional musical scoring are append x}: The notes listed are then marked on the film 12 in correct advent relation by using a grease pencil orthe like. The film is stopped at each position of the said marks, individual sweep-firing signals from switch Skate magnetically imposed thereon at head 34 and the film is returned to the start position. Thereupon the oscillator 3 is adjusted by the aid of a chart which correlates electronic frequencies with music notations and the selected pitch is auditioned at speaker 8. The volume controls of the polyharmonic injector 4 are adjusted to inject the various harmonics required. The amplitudes of the yarious harmonics which,as in the case of the oboe, may be stronger than the fundamental, are provided in chart form as exemplified in the percentages shown in Figure 7. The sustainedcomplcx wave which is put out froimthe polyharmonic generator 4, as controlled by the percentage,settings, becomes subject to atransmission loss provided inthe variable transmission element 37 Whichis controlled by the operating potentials from the photocell 22 Referring to the oscilloscope display at 21, the variable transmission element 37 will tend to integrate thellpulses and .be conductive in the rectangular display region .below the contour 20 and will switch on deletingv or. blanking potentials whenever the spot leavesthis region and is above the envelope contour drawing Zi). The rate at which the switching occurs is determined by the ultra sonic oscillator frequency from 27. The length of time during which the contour-controlled switching operation will lastis determined by the selection of. the single sweep time-basein the oscilloscope provided. In. this way the time-b seldetermincs the .duration in which the note or touch ofmusic is sounding. Integration of the .varying switching pulses in element 37 is provided exponentially according to well known electronic practice. Single sweep scanning of the envelope is initiated by push button control 35 and in thismanner the combined complex tone from 3 and, 4 is prepared and can be auditioned. at speaker outputit. The grease pencil outline of the envelopercontour. Ztlmay be'modified by erasures until the musical; note has the precise qualities which are desired.- The/correct recording volume 'level is obtained by ad-- justment .of the mixer control 44.
and the single sweep switch 32 is. turned to automatic con: trol byusing the firing. signal from 34,. Arccording-is. then made wherein the prerecorded advent signals onthe film edge ensure the precise envelope placemeutofeach repetition in the scorelof the note which hasbeen thus tailored.
Additional frequencies of the same.,touch. and. char acter may be produced by. simple adjustment of theaudio. oscillator The previous record, of sweepfiring signals may be erased by switching in, the oscillator 27 atswitchi 32 and anew note-timing advent-recording made Thc incoming recording from the variable transmission element 37 is auditioned in mixed-44formatwiththe playback signal from head 9.; If found satisfactory, it is. rerccorded on the same track by head 11- concurrently with .an. in-, tervening erasure at head), virtually accomplishing the superposition of anadditional. recording.v It .will be apr. parent that the numberof rcrecordiugsemployed before undue loss from noise destroys the dynamic range .may. be limited. Therefore, the number of notes, of different pitch which may be prepared by the mode outlined will belikewise limited. Amodification of the above mode may be followed wherein all non-concurrent notes which:
are tohave the same harmonic structureand the .same envelope are grouped by each of the pitches prescribed, in the score. The required advent times are, pencil. marked on the film and followed by, the reeojrding34 of all sweep-firing signals. The-magneticfilm isposi tioned to theadvent marks, and is backset. to iucludean, acceleration footage. The audio oscillator 3 signal at each pitch which is required is recordedfor a time which; is longer than the intended lengths of thefinal notes.- In, this manner, anumber of fundamental tones may be.-re, corded thereby reducing the number of rerecording operations, On playback, these various sustained recorded tones areswitchedSZ to feed the polyharmoniegenerator 4 through fll, 42, and 4.3 and are enclosed in the prepared sound envelope contour as outlined. The timing,adventsignals initiate the whole serics of envelope decayperiods of one typeused in the score thereby rerecording notes of different frequencies on the same track in. one operation.
In the synthesis of notes ofcertain instruments such as the piano, where tones concurrently sound on three, strings, an enharmonic structure which issiniilarmaybe obtained While performing the rerecording. This maybe accomplished .by concurrently connecting the demodulator 38 (connection notshow n with a very low frequency from the audio, oscillator. switch 39 beingclosed. The re; sulting low frequency amplitude modulation produces dif-.. ference frequencies with each ofthelfrequencies mime. complex envelope-enclosed noteslwhichiare being rere corded. Other enharmonic efiects can be obtained byintroducing the said I amplitude modulation at theitime the recording lot the sustained fundamentals are made;
Authentic; triple string effeets are obtained byprerecordingthree complex frequencies in superposition each..fre-.. quency-beingdisplaccd by a smalldifference from the previous one, recorded. The, triplerecordings -of.sus-. tained strings are located covering eachposition where notes are to appear. The single sweep-firing signals are recorded and the prerecordings of the sustained notes are played back through the variable transmission elementwhich deIetesthcnr down toenclosure in a given piano touch envelope to bc rerecorded again in the manner' described.
Referring now to Figure 8 which is a schematic VI-CV? of a modification of a portion of the recording arrangements diagrammed in Figure 2, a simple duplicationv of the playback erase and recordmagnetic heads andass'oci ated switches is shown. The advantages of this modi fi c tion will be vapparent in that all/the aforementioned s thetic recording operations may be duplicated onjeach track and triple mixing operations performed. Synthesis The .output. of thc recording amplificrs45 is turned'to record, by. switch ,46;
of chords may be achieved and multiple instrument recordings prepared. While magnetic film 12 is shown, the use of magnetic tape for a twin track system would be preferred. When magnetic film is used, however, multiple tracks may be recorded by utilizing heads 105, 106 and 107 having transverse position-ability and the delimitation of the method thereby is very complete.
A further advantage may be obtained by making successive superposed recordings without intervening erasing operations. In this case the recording apparatus is adapted to enable the following novel method of dualtrack recording to be utilized:
In Figure 8 postulate that a sequence of notes has been recorded on both tracks, it being desirable to superpose a secondary sequence of overlapping notes thereon. To effect this without the recorder A. C. bias current partly erasing and distorting the existing recording, head 107 is reconnected in lieu of head 105 and the volume of the resulting rerecording which is possible at head 11 is adjusted to neither add nor detract from the recording which exists on the track under head 11, the erase control 108 being turned off.
During this operation the aforementioned secondary sequence of notes may be introduced through the variable transmission element 37 and a superposed recording of the same added to the track under head 11. The recording system connections are thereupon switched to enable head 11 to pick up the superposed mixed recording which has been made to record the same in a similar manner on the track under record head 107. No signal is introduced through the variable transmission element 37 in this step which is a transfer step to enable both tracks to have the same record. This novel operation is introduced to enable the history of the successive polarization positions of the particles on the recording medium which comprise the prior recordings, appropriately to modify the operating center of the A. C. bias signal of recorder so that the incoming additional recording may include the aforementioned magnetic history.
Referring now to Figure 9, the advantages of the method of this invention are further greatly enhanced by the multiple magnetic tape repetition recording arrangement shown. The pressure idler 110, which is releasable, enables the concurrent driving of the multiple loops of magnetic tape in the direction of the arrow 111. The loop-driving motor 112 may be separate from the main recording motor drive of the system. The magnetic heads 113 may act in playback, recording, and erasing functions. The associated connections and switchings which are not shown are well known in recording practice. The predominant value of the multiple loop arrangement centers in the feasibility of prerecording a number of prepared notes of any kind, the whole or any part of the same being auditionable in parallel while the individual onsets of each note may be manually repositioned by moving the relative position of the appropriate loop. Further advantage in the method accrues from the fact that part orchestrations or chords may be auditioned in whole while an undesirable component may be disclosed by switching off the offending track. It will be apparent that the above advantages may be also achieved in the modification diagrammed in Figure 8 by the use of a number of heads wherein each head combines the functions of heads 105, 106 and 107 thereby enabling the recording of a number of tracks substantially as described in connection with Figure 9. The repetitive feature of the recording loops may be achieved by consecutively switching the recording motor into reversing the magnetic film 12.
In the mode and method of the invention the multipletrack multiple-head alternative to the heads 105, 106 and 107 is preferred and is illustrated in Figure 1. The further modification embodied in the multi-loop combination shown in Figure 9 is desirable where extreme deliberation and perfection of synthetic recordings is required.
Referring again to Figure 1 wherein multiple-track recording is envisaged, the operation of the method may be 10 further described in the mode whereby percussive struc tures in music may be prepared. A recording is made of substantially high audio frequency. A second recording is made of a frequency which differs from the previous record by a small number of cycles. The recordings should overlap by a margin in total footage which is to contain the percussives to be recorded. The two frequencies are switched at 52 to playback through the demodulator 38 as shown in Figure 2. The resulting low frequency output is fed by 39 to control the variable transmission element 37. Concurrently the audio oscillator is set to furnish the fundamental frequency required and the prescribed harmonic percentages are enclosed by element 37 in the envelope contour which is scanned when initiated by pulses from 34. The combination with the above low frequency modulations creates difference frequencies as is well understood in electronic practice, the result being an enharmonic ringing which may be recorded. To the arrangements existing when the envelope note is re corded two modifications are made; namely, the time-base which was used is reset to be substantially 10% of its former value and the oscillator frequency is adjusted to a somewhat higher frequency. The full length envelope note is played back and rerecorded concurrently with the short, 10% envelope note so that both have identical advent times in the mixed rerecording thereof. The percussive effect which is produced may be controlled over a wide range by the selection of the impact pitch or complex wave contained in the shorter envelope.
A further mode of operation whereby tremolo effects of the frequency-modulated type may be carired out consists in prerecording the fundamental frequency required so that the recording is longer than the final footage required-the playback thereof being amplitude-modulated with a low audio frequency and made to directly control the transmission element 37. The result is rerecorded on an adjacent track. The two recordings are mixed and injected into the polyharmonic generator 4 at the prescribed percentages. The resultant frequency-modulated waves are enclosed at transmission element 37 in the designed envelope and rerecorded on the assembly track in the locations which are prescribed by the advent record from head 34.
Tremolo effects of the amplitude-modulation type are.
achieved by prerecording all the fundamental pitches pre scribed, adjusting the audio oscillator to furnish the amplitude modulation frequency to the variable transmissionelement 37, concurrently playing back the prerecorded notes and injecting the same into the prescribed setup of harmonic and envelope structure, the resultant amplitudetype tremolo notes being rerecorded.
A further mode of operation consists in the use of envelopes of playing touch which are characteristic of certain instruments as the trumpet, while the harmonic structure which is selected is characteristic of a very different class of instrument as a violin. The harmonic structure may be varied while the envelope is being scanned. Recordings prepared in this manner cannot be obtained from any musical instrument made heretofore and they are of great interest to producers of music.
Another mode of operation consists in the modification of sounds which are derived from a microphone. According to the method, new envelope structures maybe assigned and new harmonic adidtions may be injected. The envelopes enclosing the live sound source may be extracted in the demodulator element 38 or by the recti' fication of a double-sideband suppressed-carrier ultrasonic control-signal, the resulting live envelopes being used to enclose totally new complex wave structures such as that derivable from a sustained singing or speaking voice.
Another mode of operation consists in the audible playback of a prior recording-whereby a singer may a'ccompany the same'ove'r a microphone input and be concu'r rently'rerecorded with the original voice or with any other 1 1 complex characteristicfrequencywhich may be set up on the polyharmonicgenerator.
Afurther mode of operationaccording to the invention,
consistsudnerasing arecorclcdnsustained, frequency. to accord with the contours ,whichare to be applied, the erasing being effected at recording speedby electronic means. Referring to Figure, 2, theerasing contouring sig-.. nalmay be obtained from the photocell output at-22 which.
isconnected to the record amplifier 45, the bias oscillator 27; being. disconnected therefrom, therecord head .11 functioning as, an erasing element. Alternatively the erasing contouring-signal may beobtained from the oscillator 27 beingmadesubject to variable transmission by feeding. the signal through element BTwhich is made-subject to. dele-.
tions'by the contouring-signal fromphotocell 22.- The variable transmission element may be connected at thev controlsighalinput to audio-signals which may be derived from prior recordings or from the microphoneinput,
and the oscillator output residue from element 37 after. amplification ,through 45 being ,used to delete the prereresidue of which after contouring is played. back through thedemodulator 38, the resulting audio, being utilized for further recording or auditioning in: the conventional anure Referring now to Figure 10, a possible alternative to thephotoelcctric system of scanning of a drawing or outline of desired envelopes, ,as shown in Figure 2, by parts 17 p to 2 4 and 28 to-37 inclusive, is the method of directly erasing a wide track of a recording of the sustained. tone which has v been prepared. According to the invention, the sustained. tone is prerecorded on a Wide. tape loop of a magneticmedium 114 by the wide-track magnetic head 115.v A masking cut-011L116, or the mental equivalent is disposed on the stationary loop .as dotted at 11-7.- An A. C. or D. C. operated or magnetized erasetpcncil 118 is made to erase all the complex wave striations which have been recorded excepting only that region protected by themask of the required envelope of the desired note. The loop of recording residue which remains and which comprises the. desired note is rerecorded as often as the note is prescribed to appear inthe synthetic record of music which is being assembled. The main recording drive motor 48 in Figure 2 or an equivalent interlock or synchronous system is used M48. in Figure 10. A synchronous relationship is preferred as a means of ensuring thetransferof theprecise placement of the onset time of each note to be rerecorded. While this alternative arrangement of theelements in the system will' enable the: method of the invention to be performed, it is not preq.
ferredin that an individual envelope shape is required for each. change in decay time or length of a given note.
A further alternative to the photoelectric scanning ofa drawing or outline. of the desired envelopecontour is the arrangement shown. in Figure, ,11' which ,is. preferred over the arrangements of Figure 10, It is not a preferred alternative to the photoelectric scanning of envelope designs,
Referring n w to F u ec as a sne q -s oscillator 120 isrccordedfor one revolution of the magnetic loop 121 by means of the wide-track head 1 22. The
control signal recording, which otherwise provides a sustainedloutput rectified signal from an amplifienand re tifier 123 is modified manually bymagnetic: erase-pencil deletions. The required envelope design may be a cu tout l 24 disposed to guide the activitiesof theerase pencil 118 on the stationary recording. Precise ,positioning of the; onset is marked on thejtape' by grease pencil, said mark correspondingwith. the advent markonthhssembly recording film. The main recording drive motor isrelatedby drive tothe motion of the loop 121 by meansof the speed-changer element 126 underspeed-reduction control 121. The combination of these elements enables a single designof envelope to be precisely located as to the advent time of the envelope placement while a wide, range of envelope duration times may be directly selected through speed-reduction control 127. The erasure of the control signal recording, wherever unmasked by the cut,-. out shape of the desired envelope, enables the variable gain transmission element 37 to transmit substantially the shape erased as in the control signal.
While the instantaneity of playback of magnetic recording systems is of particular advantage in the recording and,
rerecording assembly of the components of music according to the invention, the operations may be performed, by means of suitably modified disc recording elements.
In disc recording according to the invention the precise location and placement of the various advent times of the noteswhich are being recorded may be achieved by pre-.
recording the prepared notes in a concentrically arranged series on a source disc suitably marked with peripheral indexing cues, and rerecording notes selected therefrom onto a synchronously interlocked second recording disc.
The musical notes which are to be prerecorded are pre--- pared according to the method and means which have been described in connection with Figures 1 and 2 using to perform the same operations by utilizing a single turntable and recording channel in combination with two or more playback pickups and mixing means which feed the recording head for concentrically related rerecording functions. In this case the indexed disc of prerecorded notes as prepared is of larger diameter than the disc which is to receive the assembled rerecordings of the notes. Thus the smaller disc is superposed on the larger source disc which is manually indexed in relation thereto in accord with the precise advent locations of notes as indicated. Where overlapping notes in the production of chords, etc. are indicated the rerecording operations will' involve alternation from the upper to the lower and outer disc area and vice-versa, the ease of positioning and exchange of the records being an advantage over other systems of recording.
In the case ofoptical methods of recording the method of the invention may be applied by utilizing a number of filmphonographs working in synchronous combination with a mixing and rerecording facility as is well known in motion picture practice. With such facilitiesit is necessary to make prior recording and processing of a film library of sustained frequencies having every pitch and instrument characterization as prescribed in the music score to be assembled. Appropriatefootages of these sustained tones are out together according to the necessary' spaced apart relationships as indicated in the music score, for all notes which are to be in non-concurrent placement in the final recording. Additional reels of ap-, propriately spaced apart sustained frequency optical film footage are prepared for those parts of the music score which require overlapping notes. By fecdingthe filmphonograph playback signals from the reels tothe contou r deleting element and combination as described in Figure 2, parts 17 to 37 inclusive, each frequency may be deleted to a residue of the appropriate touch as'determined by the contour pattern employed. The firing of the single sweep scan is conveniently produced by connecting the playback signal to the single-sweep firing circuit of the oscilloscope according to the mode outlined in connection h Fi ur Another neans for the contour-deleting operation ac: cording to the method of the invention consists in the application of opaque matter to the sound-tracks ofthe.
prepared reelsof selected sustained frequency recordings. The opaque material may be manually applied by pencil, brush or air-brush according to masks or templates of contours as determined by experience or by study of sound amplitude contours as exemplified in variable area motion picture film recordings of mechanical musical instrument sounds.
A further means for the contour-deleting operation of the invention consists in the preparation of sound recordings of a control. frequency whose amplitude is varied at the time of recording according to contours electronically derived from noise-reduction signals which are produced in motion picture optical recordings, and which have been initiated by the pickup of mechanical musical instrument sounds. The control frequency contours thus recorded are processed and collected in a library for convenience in the assembly of the aforementioned reels of sustained frequencies in appropriate relationships as prescribed in the score. In playback the sustained frequencies are connected to feed through a variable transmission element which is controlled by the synchronous playback signals from the control frequency contour reel described above. The resulting residue of the sustained frequencies is rerecorded in mixed relationship with additional concurrent playback of the overlapping sustained frequency reels and control frequency contour reels as required by the musical score in assembly. It will be apparent that the operation of individual advent placement of control frequency contours is manually effected at the time of the cutting together of the film reels in their preparation.
To enable the rerecording of the overlapping sounds on the reels which have been prepared as described, it is necessary to duplicate the deleting element and combination as described for each concurrently operable filmphonograph facility which is employed. The multiple outputs of the prepared residues from each of the reels involved are mixed at the appropriate volume levels and rerecorded optically by means of a standard film sound recorder. The resulting recording is processed for playback according to motion picture practice.
It is to be understood that the word recording as used in the appended claims refers to playable sound-tracks disposed on a suitable recording medium as exemplified in mechanical, magnetic or optical recording sound-tracks on disc, tape, wire, or film.
What I claim is:
1. A method of producing sounds comprising the following steps, producing an audio frequency current, making an envelope contour according to a progression of instant amplitudes of sound, variably controlling said audio frequency current until the residue of said audio frequency current conforms to the said envelope contour, and reproducing said residue.
2. A method of producing recorded sounds comprising the steps of producing an electric current corresponding to a sustained sound frequency, making an envelope contour according to a progression of instant amplitudes of sound, deleting the amplitude of the current corresponding to the sustained sound frequency until the residue conforms to the envelope contour, recording said residue of the sound frequency according to given advent placements on the sound-track of a recording.
3. A method as defined in claim 2, in which the step of producing a sustained sound frequency is carried out by injecting a given frequency into an aperiodic polyharmonic generator, adjusting the amplitude of the injected frequency, adjusting the amplitude of each of the harmonic frequencies generated and combining the adjusted frequencies in a single output.
4. A method as defined in claim 2, in which the step of producing a sustained sound frequency includes producing specified and individually adjusted harmonics from any given frequency by the steps of rotationally displacing more than one phase therefrom, maintaining a constant phase displacement between the displaced phases by utilizing staggered cascaded phase rotators and distributing the polyphase outputs produced around an equipotentiometric ring of resistors, feeding the outputs from individual rectifier groups connected to appropriate polyphase points in said ring of resistors to individual square law amplifiers, further feeding the specified harmonic outputs resulting therefrom through individually adjusted volume controls to a combining output network.
5. A method as defined in claim 2, in which the step of producing a sustained sound frequency includes producing specified and individually adjusted harmonics from any given frequency by injecting the given frequency into an array of square law amplifiers and adjusting the amplitudes of the various specified harmonic outputs therefrom, and utilizing the specified harmonics to outphase other output frequencies which may be concurrently generated.
6. A method as defined in claim 2, in which the step of deleting the amplitude of the current corresponding to the sustained sound frequency is carried out by sending the said current through an electronic variable transmission means subject to a control signal, scanning a single sweep oscilloscope image of the said control signal by protoelectric means, covering the oscilloscope display with a desired opaque envelope contour disposed on a transparent surface and connecting the modulated photoelectric control-signal output resulting therefrom to the control terminal of the said variable transmission means.
7. A method as defined in claim 2, in which the step of deleting the amplitude of the current corresponding to the sustained sound frequency is carried out by recording the said frequency on a wide sound-track, disposing an envelope contour guide upon said sound-track while stationary, and obliterating a part of the recording of said frequency until the residue conforms to the said contour guide.
8. A method as defined in claim 2, in which the step of deleting the amplitude of the current corresponding to the sustained sound frequency is carried out by sending said current through a variable transmission means subject to a control signal, recording the control signal on a wide sound-track, disposing the envelope contour upon said sound-track while stationary, obliterating the recorded control signal until the recorded control signal conforms to said envelope contour and controlling said transmission element by the resulting residue of the recorded control signal.
9. A method as defined in claim 8, in which the resulting residue of the sound frequency is recorded according to a given advent placement on the sound-track by synchronizably and identifiably relating it to the advent time of the recorded control signal by interlocking the driving means of said sound-track of said residue of the sound frequency and of the wide sound-track of the control signal, feeding the output of the variable transmission means through manual gain controlling means to the input of the recording means for said sound frequencies to be re corded and recording said residue of the sound frequency according to a given advent and assembly placement on the sound-track by the further step of playback of the wide sound-track control signal.
10. A method as defined in claim 2, in which the sustained sound frequency is recorded, and the step of deleting is carried out by obliterating the recorded sustained sound frequency to accord with the envelope contour by superposing a recording on the recorded sustained sound frequency.
11. A method as defined in claim 2, in which the sustained sound frequency is recorded and in which the step of deleting is carried out by superposing an erasing frequency which has been modulated with sounds.
12. A method as defined in claim 2, in which the sounds produced are notes in a musical arrangement and whichincludes: the step ofrecording the notes nonsequentially .according to deliberated advent placements;
13. Armethod as defined in claim 12, in which the steps of recording are performed magnetically.
14.- A method as defined in claim 2, in which the step of making the envelope contour is performed by electrically integrating a progression of instant amplitudes of sound and by utilizing the integration so obtained to control a variable transmission means which is connected to delete the sustained frequency.
15. Amethod as defined in claim 14, in which the variable,,transmissionelement is controlled by a carrier fre quency modulated with the integration of the progression of instant amplitudes of sound.
16. A method of producing recorded sounds in which predetermined advent placements of sound in the recordingon a first sound-track are obtained, comprising the steps of recording a sweep initiating signal on a second soundtrack at given advent points, the second sound-track being synchronously related to the first sound-track, using a playback signal from the second sound-track to initiate a-single sweep of the beam of an oscilloscope, connecting the oscilloscope to display a frequency image of an oscillator output signal, superposing a given contour on said image, photoelectrically scanning a part of said image as defined by said contour, utilizing the photo-electric current to control a variable transmission circuit, transmitting through said transmission circuit currents corresponding to sound waves and recording the resulting residue of sound according to the recorded sweep initiating signals.
17. A method of recording notes in a musical arrangement. in: which the notes are recorded nonsequentially comprising the steps of recording a given sustained sound frequency on an endless sound-track, deleting the recording of said given sound sustained frequency according to a progression of instant amplitudes of a secondary sound, rerecording the residue of said recording and synchronizably and identifiably relating the advent placement thereof by interlocking the driving means of both recorders.
18. Apparatus for producing sounds comprising a source of currents corresponding to sound waves, an electronic demodulator for forming currents corresponding to the envelope of the amplitude variations of said sound waves, a source of sustained audio wave currents of given complexities, an electrically-controlled variable transmis sion means connected to transmitand adapted to delete said sustained audio wave currents according to said envelope and means for reproducing the residue current output from said transmission means.
19. Apparatus as defined in claim. 18,-in which the source of currents correspondingto sound Waves is a microphone pickup.
29. Apparatus as defined in claim 18, in which the sourceof currents corresponding to sound waves is a sound record operating a pickup head. I
21. Apparatus as defined in claim 18, in which the reproducing means includes sound'recording and playback elements. v
22. Apparatus as defined in claim 18, in which the source of sustained audio Waves comprises a source of currents corresponding to sound waves in combination with constant amplitude maintaining means for sustaining said audio waves.
23. Apparatus as defined in claim 1B, in which the source of sustained audio waves is an audio oscillator in combination with a polyharmonic generator.
24. Apparatus for producing sounds comprising the combination of a source or" audio frequency currents, an electrically controlled variable transmission means for varying the transn'iission of said audio irequency currents, at source of control currents for controlling said variable transmission means, a surface adapted to modify said control currentsaccording to sound envelope contoursdisposed thereon and means for reproducing the residue of audio frequency current in the output from said transmis,
25. Apparatus as defined in claim 24, in which the surface is a transparency adapted to modify the luminous display from an oscilloscope for displaying an image of said control currents, and which comprises a photocell arranged to scan the modified luminous image and to have its current output varied in accordance therewith, the variable transmission element being arranged to be controlled by said current output of the photocell.
26. Apparatus as defined in claim 24, in which the surfaceadapted to modify the control currents is a recording of said control currents arranged so that the playback currents therefrom control the variable transmission element.
27. Apparatus for producing sounds comprising a source or" audio waves of given complexity, variable transmission. means for controllably transmitting the said waves, a source of control current for controlling said variable transmission means, means for modifying said control current in accordance with photoelectrically scanned contours of given sound wave envelopes, means for initiating the photoelectrical. scanning of said contours according to recorded given advent signals, recording means arranged to record the output currents of said variable transmission means in synchronous relation with said recorded advent signals.
28. Apparatus for producing recorded sounds comprising a source of audio waves of given complexity, variable transmission means for. controllably transmitting the said waves thercthrough, a source of control current for con trolling said variable transmission means, means for capacitatively modifying said control current in accord- .nce with a scanned contour of a given sound wave envelope, means for initiating the scanning of said contour according to prerecorded given advent signals, recording means arranged to record the output current of said variable transmission means in synchronous relation with said prerecorded advent signals.
29. Apparatus for the generation of currents of given complexity from a source of current. of any given frequency comprising plural phase rotating networks having constant phase rotation relationships therebetweenconnected to produce polyphase rotation of currents in an equipotentiometric ring of resistors, progressive polyphase points thereon connected to individual rectifierelements having parallel output circuits connected to the input circuits of individual square law amplifier tubes which are connected to manually operable volume control means connected to a common output terminal.
30. Apparatus for producing recorded sounds compris-.
ing an electronic generator of sustained audio waves, a polyharmonic generator connected thereto, an electrically controllable variable transmission means connected to the output of the polyharrnonic generator, a generator of a secondary frequency connected to a contour determining means which is connected to control said variable transmission means, said variable transmission means being connected to sound recorder elements whichare adapted to automatically initiate the said amplitude controlling means to record according to predetermined advent positions on said recording.
31. Apparatus for producing two or more signals having essentially constant desired. phase displacement relations to each otherthroughoutan extensivefrequency spectrum comprising, a source of signals within said frequency spectrum, a separate channel associated with each of the desired phase displaced signals said channels being fed in parallel by said source of signals, said channels each comprising a series of cascadedstages, the number of said cascaded stages preferably being of the order of at least one per decade of frequency spectrum; each of said stages in each channel comprising, phase inverting means operable throughout said frequency spectrum whereby equal output signals difi'ering in phase by degrees are provided between a reference phase terminal and two output terminals, a phase shifting pair of impedances connected in series between said. two output terminals, the input terminals of the succeeding stage in the channel being connected between said reference phase terminal and the common junction point of said pair of impedances; the phase displacements of the said phase-shifting pairs of impedances of the stages in each channel being selected to provide phase rotations progressively stage by stage throughout said frequency spectrum, the phase displacement of each corresponding stage in the said separate channels being selected to provide phase displacement relative to each other equal to the desired relative phase displacement between the outputs of said channels.
32. An aperiodic polyharmonic generator comprising a source of signals of fundamental frequency, an array of two species of square law amplifiers, means to apply to the input of the first of said species of amplifiers fundamental and odd harmonic signals as generated within the array by the second species of said amplifiers, the output of said first species of amplifiers containing double frequency components of the input signal, means to apply to the input of the second of said species of amplifiers both double frequency signals as generated by said first species of amplifiers together with odd harmonic signals, the output of said second species of amplifiers containing sum and diiference frequency components of the input signals, and means to apply to the outputs of both species of amplifiers out-phasing signals as present within the array said out-phasing signals being arranged so as to cancel the undesired frequencies present in said amplifier outputs.
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