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Subject: RE: Encoder/decode Chips
From: VanBaren, Gerald (AGRE) (Gerald.VanBaren_at_smiths-aerospace.com)
Date: 2004-04-22


1) You could look at ADPCM (G.726 and/or G.729 I believe), but they are designed to be telco bandwidth (3KHz bandwidth, 8K samples per second sample rate). You may be able to overclock an encoder chip to get higher bandwidth, but you would be very non-standard.

2) Your bandwidth and sampling rates don't compute (you may simply have them backwards since your bandwidth spec is in kbps and sample rates in khz).

3) MP3 at 32K samples/second gives you a bandwidth of 16KHz MAXIMUM so it is a pretty close match to your requirements (assuming your bandwidth is 6KHz-11KHz). I personally would advise not going below 32K samples/second on a 11KHz signal since Nyquist was an optimist (2x is the theoretical minimum but real life conspires to make it pretty dubious that you can achieve a reasonable result at only 2x sample rate).

gvb

> -----Original Message-----
> From: rockbox-bounces_at_cool.haxx.se
> [mailto:rockbox-bounces_at_cool.haxx.se]On Behalf Of Fox
> Sent: Thursday, April 22, 2004 2:07 PM
> To: rockbox_at_cool.haxx.se
> Subject: Encoder/decode Chips
>
>
> Hey all,
> I'm working on my senior project for my BS degree in computer
> engineering.
> My project works with low bandwidth audio and I'm looking for
> some chips
> that will permit voice compression (and a chip that will
> decompress) with a
> bandwidth range of 8kbps to 28kbps. sampling rate of
> 6khz-11khz mono. MP3 is
> ideal but not not nesassary. The chip thats used in the
> archos only encodes
> down to 32kbs making it unsuitable. Can anyone point to some
> chips that will
> fulfill my needs?
>
> -Fox
>
>
>
> _______________________________________________
> http://cool.haxx.se/mailman/listinfo/rockbox
>

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