Re: Voice compression

CVSD uses a bit-serial data stream. Harris datasheets for obsolete Codecs are HC55516, HC55532. The "recording"-circuit can be an analog hack ( Kop, flipflop, 4 Bit shiftregister ) that sends data via SPI.
The "playback" would have to emulate this circuit in software and output
via a 8 bit D/A ( R2R resistor network, but serial ICs may be easier in SMD ).
16kBit/sec is very moderate quality, 24kBit/sec more reasonable.
We used these in the 80ies for digital answering machines in cars for the analog telephone system via radio that predated GSM in Germany. 24kBit was for incoming messages in RAM, 16 kBit for the fixed messages from EPROM. CVSD was ok, as the analog radio was a bit noisy
anyway.
At 32kBit/sec ADPCM is better, but you probably do not intend to use a 64kBit PCM codec as a frontend. If you use a handset or a digital
PCM-link, the quality of CVSD may be not competitive. For playback via
a loudspeaker sufficient, there is usually enough background noise.
MfG  JRD