Can't help much but back in the 80's I used CVSD as a low rate codec (16k
bits per second) in the days when I worked on military digital comms.
Rubbish quality but really resistant to bit errors (up to 10%) which makes
it ideal for radio links. Try 10% errors on a PCM system !


Robin Abbott
Forest Electronics
robin.abbott@fored.co.uk
www.fored.co.uk 
 

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
Jinx
Sent: 30 September 2007 23:55
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] Talking PIC's !

> MP3 playback would be much more efficient on memory storage but I 
> suspect would be a nightmare on processor load !

Robin, apologies if this slightly hi-jacks your thread

I was looking into something like this last week. There used to be a really
great Texas chip, the TMS3477 / TMS3478 that had pretty wonderful
reproduction using CVSD. Texas obsoleted it, bless them.
Luckily I grabbed a few dozen (Google for it - good luck)

http://en.wikipedia.org/wiki/Continuously_variable_slope_delta_modulation

Originally it was designed to use DRAM, approx 10s per Mb at a good sampling
rate (pretty acceptable music quality). I made a series of PIC-supervised
logic convertors so it could use EPROMS and SRAM, in banks if need be for
extended play. A little expensive, but the sound quality of the application
was worth it. Basically the recording was still done with DRAM base unit,
then copied and re- stored in the product's parallel memory

That was in the way-back-when days of the 16F84A-10. I'm sure that now an
18F or dsPIC could handle CVSD directly, perhaps with the assistance of an
external fast DAC

Has anyone come across such an implementation ? I notice there are some
telco products for a possible chip solution, but they don't seem to have
been made with the same end use as the TMS3478

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