Gerhard Fiedler <geraldo@NW.COM.BR> wrote:
> I have a rather old ZyXEL 1496 around, it has a DSP based design and
> supports CELP (and ADPCM).

Yes, all modern modems are DSP-based.  There's no other practical way to
build a high-speed modem.  There were some V.22bis modems (2400 bps) that
were implemented using "traditional" (i.e., analog, non-DSP) techniques,
but I don't think any V.32, V.32bis, or V.34 modems have ever been designed
that way.

But the point was that a PIC is not going to be able to do CELP.  It can't
do DSP operations (multiply and accumulate) fast enough, and it doesn't have
enough memory.  CELP uses *huge* tables.

Even the ITU-T standards for ADPCM are beyond the capabilities of a PIC,
although it is barely possible that some simpler ADPCM algorithm might be
workable.

Cheers,
Eric