The data rate of speech and non-speech audio is selectively reduced by respective compression techniques based upon the information content of the type of signal. A composite audio information signal formed of speech and non-speech audio is applied to both a voice encoder and a wide-band audio...http://www.google.com/patents/US5809472?utm_source=gb-gplus-sharePatent US5809472 - Digital audio data transmission system based on the information content of an audio signal 
