On Fri, 17 Dec 2004 22:46:44 -0500, Robert B. wrote:
>=A0Almost certainly it used a decoder chip. =A0DSP's are fast, but not=20
> *that*=A0fast.

Huh? What do you think is inside most every MP3 decoder chip or audio
Codec? They may not come right out and say it but it's generally a DSP
core of some kind with hard coded MP3 decoder and (usually) EQ software
as well.

>=A0The decoder chips aren't all that expensive, about $10-$15, and=20
>=A0simplify the project enormously. =A0Unless you're just looking for a=20
>=A0pain in the rump, I'd say get one of those. =A0If you want to do it i=
n
>=A0software, you're going to need something more like an ARM7 or ARM9 to
>=A0get it done.

You are right on about this. I've just gone through this exercise on a
PDA project I'm working on. MP3 decoder chip vs. doing the decoder in
software. MP3 decoder adds about $10 in cost, but is a more or less
"drop-in" design. Software decoder requires development time and
assumes you have the CPU horsepower to do it.

We have an 400MHz Intel PXA270 xScale CPU so we opted for the software
decoding.

Another consideration with software decoding is do you really want to
write an MP3 decoder? With the ARM chips there's already quite a few
Open Source MP3 decoder drivers out there. We're using one with
embedded Linux.

>=A0I'm not saying it can't be done, but I suspect you'd really have to=20
>=A0water down the mp3 quality. =A0There is an AVR chip out now that has =
a
>=A0built- in mpeg decoder that might be worth looking into if you're not
>=A0set on working magic with a dsPIC.
=A0
The dsPIC isn't that great a DSP chip to begin with. In fact, I like to
call it DSP-lite... ;-) I'm not bagging the dsPIC, I think it opens up
some new and very useful possibilities that didn't exist before. Bust
as a DSP it really doesn't compete with offerings from TI, Freescale,
Analog Devices, etc. and wasn't meant to (except maybe on the low end).

Matt Pobursky
Maximum Performance Systems

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