4.1 Adaptive - Quantizer Pulse Code Modulation APCM
This is simplest time - adaptive technique, in which the quantizer step size D varies in proportion to the short - time average speech amplitude.
The implementation of APCM:
1. variable step size or gain:
2.the size of the time window:
3.feedforward or feedback adaption
- instantaneous - use short windows
- syllabic - use longer windows
4.2 Differential Pulse Code Modulation DPCM
DPCM transmitter encodes only the difference between successive samples and the receiver recovers the signal by integration.
Practical DPCM schemes incorporate a time - invariant short - term prediction process and it is called predictive differential coding.
4.3 Pitch - adaptive predictive coders APC
- LTP employed
- forward adaption