In an ADPCM coder and decoder including a so-called locking-unlocking adaptation speed control, the adaptation speed is locked to a very slow, almost constant, speed of adaptation for voiceband data and partial band energy signals, i.e., tones and tone like signals, and is unlocked to achieve a fast...http://www.google.com/patents/US4677423?utm_source=gb-gplus-sharePatent US4677423 - ADPCM coder-decoder including partial band energy transition detection
