MC145532
DESCRIPTION
An Adaptive Differential PCM (ADPCM) transcoder is used to reduce the data rate required to transmit a PCM encoded voice signal while maintaining the voice fidelity and intelligibility of the PCM signal. The transcoder is used on 64 kbps data streams which represent either voice or voice band data signals that have been digitized by a codec (e.g., MC145557). The transcoder uses a filter to attempt to predict the next PCM input value based on previous PCM input values. The error between the predicted and the true PCM input value is the information that is sent to the other end of the line. Hence the word differential, since the ADPCM data stream is the difference between the true PCM input value and the predicted value. The term “adaptive” applies to the filter that is performing the prediction. It is adaptive in that its transfer function changes based on the PCM input data. That is, it adapts to the statistics of the signals presented to it.
DECODER INPUT DDI Decoder...
