You'd need a pretty good DSP to handle MP3 encoding (and a fairly serious
encoding algorithm). To give you an idea, most docs will say you need at
least a 486 just to DECODE MP3. On my P2-300 128MB with the Xing MPEG engine
(about the fastest fair quality (Fraunhoffer's still better) of Audio
Catalyst 2 I get about 4x ripping off a CD.

However there are chips around that should do the job. The only problem is
whether or not you can pump 32 channels into less than 32 CODECs. I'd
imagine it'd be possible with an audio stream like PCM with fixed size
blocks and so on. However, MPEG uses a different kind of data stream (don't
know technical details just knows it's different so it might not matter).

One thing you mightr want to look at it USB. I have no idea on how difficult
it is to implement a host USB device (you could use a PC easily) but other
than that it has a few notable advantages:
        - There are specs for digital audio (including multiple data formats
like PCM, MPEG etc...)
        - If you get USB capable hardware it'll do all the work of handling
multiple data streams including bandwidth allocation/balancing
        - You can plug it straight into a PC
        - According to some it is the next standard for Digital Audio
distribution (both in PC's and other music devices)

USB supports 2 device speeds (the device advertises it's speed): 1.5Mb/s and
12Mb/s. I would suggest 128kbit/s isn't quite high enough for CD quality. I
used to use 160kit/s but now use Variable Bit Rate. I would say VBR is the
way to go (no idea on hardware VBR encoders). In VBR the data rate is varied
to give the best compression rate for each frame (i.e. a frame with little
information will be coded at low bandwidth) thus maximising bandwidth.
For 32 channel at 160kbit/s each:
    160kbit/s x 32 = 5120kbit/s ~5Mb/s

Thus 32 channels of 160k MP3 encoded data should easily fit over a single
USB line.

VBR could increase the quality of the transmitted lines. For instance Audio
Catalyst supports VBR of various quality. At medium quality the data rate
maxes out at about 256k and size is slightly smaller or equivalent to a 160k
normal file. At high quality the data rates peaks at 320k (highest rate) and
the size is about 10% larger than a 160k file. Both these value's are for
Psychedelic Trance songs which are generally fairly 'busy' and so shouldn't
give exceptional results under VBR in terms of size.

The other thing USB allows is the use of different quality streams and thus
better use of bandwidth. For instance the fire microphone can run at a very
low bandwidth as it is speech only. Thus you save bandwidth and minimize
storage space for recording. Obviously if you use VBR this should be
unnecesaary.

For more information on MP3 de/coding check out:
http://www.spectsoft.com/mp3tech/
http://www.angelfire.com/pa2/mpx/

For info on USB standards check out:
http://www.usb.org/

Phillips makes an I2C compatible USB interface but I2C is only 1Mbits. They
also have a chip that does digital and analog audio to USB at up to 24bit
55kHz.

Intel have a USB capable MCS251 compatible MCU and an application note on
connecting it to an audio codec.

Thomas Brandon.

----- Original Message -----
> Does anyone have any mp3 encoding algorithms for dsp's which can encode
real
> time?
> If so you idea is great.
>
> > Um wouldn't it be easier to simply MP3 the audio in question and pass
> that.
> > 128kbits/sec x 32 channels = 2048kbits/second. rs-485 can handle that
> > easily.