Adaptive predictive coding of speech and voiceband data signals

We consider ADPCM coding techniques for speech and voiceband data signals that do not require previous identification of the type of signal to be encoded. After a review of the frequently conflicting requirements for prediction and quantization of these two types of signals, coders with backward adaptive prediction and backward (AQB) or forward (AQF) quantizer adaptation are discussed. We find that ADPCM-AQF possesses significant performance advantages relative to ADPCM-AQB for both speech and voiceband data signals at the cost of additional signal delay. 4800 b/s voiceband data can be transmitted satisfactorily at 32 kb/s even with multiple stages of tandeming and infrequent transmission errors, but 40 kb/s are required for reliable 9600 b/s voiceband data transmission with intermediate analog conversion.