Hi - after some looking around and trying different ones out with sound
forge XP (I have their $40 lite version for occasionally making CDs from
DAT tapes) I think ADPCM is possible with a PIC and sounds ...
reasonable.  In Sound Forge (or cool edit, but my freebie trial has
expired, so no saves anymore) try saving a clip with different
compressors, then play it back.  I did these for a 5 sec spoken word
clip @ 16Khz and 8Khz sample rates, then made a CD of the results and
played it for the client.  I didn't look into the details of ADPCM
decoder CPU crunch complexity, but compared to the descriptions of the
others, it seemed doable.

Also look at winbond's "chipcorder" parts, all-in-one flash mem +
playback.  Digikey has them.

However, I think my client has her heart set on mp3.  So, I *finally*
get to make an mp3 player!  For pay!  Yessssss!  :)

I got all my info via google searches.
For very low bitrates (13Kbits/sec range) GSM may be doable with a PIC.
  When saved in this format in Sound Forge, it sounded pretty bad.  But
its the european cellphone standard, and it must be better then what I
had.  There are free codec implementations w/source, but I wanted to get
the client's opinion before wading off into those waters...

J



Jonathan Johnson wrote:
> Jesse,
> SNIP>
> Ok back to client research.  Speech compression algorithms suitable for
> a PIC to decompress out of flash memory and play - how cool is that?  :)
>
> I'm looking at something similar at the moment...maybe we should compare
> note's
> Currently trying for the best algorithm I can get to run on a PIC or AVR,
> there are plenty of algorithms out there that work great....on a DSP.
> Best of luck
>
> Jonathan
>

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