Re: Sega sound boards...

>Nah, it works like sh*t, unless there is a lot of "true" silences (even
>the slightest noise keeps RLE from working).

Hmmmm. Good point.

>You might try ADPCM, go download the examples on the Microchip home
>page. They use a version of ADPCM that uses no floating point. As long
>as you stick to voice, ADPCM works well. Just don't try pumping any
>music through it.

Actually, ADPCM is happy with music. Music goes to hell in a handbasket
really fast if it runs through any sort of CELP or Truespeech, or DSVD type
coders (like LPC etc.). 3 or 4 bit ADPCM is good compression too-- and
like you said-- Microchip has source on their webpage. Seems like it used
the 16Cxx parts? (I looked at that a while back when researching how to
replicate Nightmare, since it uses 4bit ADPCM for samples.)

(We use ADPCM on our modems for incoming/outgoing messages-- works fine
with music/tonal content. If you try to play hold-music over a DSVD type
voice coder you get cool (but useless) "demons of hell" noises.)

I might just do a delta+key type thing. Have to analyze the data and look
at it. Basically you just code two "deltas" per byte, each capable of
going +/- seven steps. If you can't get where you need it with the delta,
you send a "key" (like 0xff) that says the next byte is an absolute value.
Depending on the nature of the data you can get either 2:1 compression, or
1:2 expansion. ;-)

If I can get the samples to fit "raw" into 1Mbyte I'd probably not even
bother with compression in all honesty...

>At these speed PWM works really well, is much cheaper, and using a
>processor dedicated to the job, could most likely be done completely in
>software. Though a 10bit PWM port like that in the PIC makes life easy.
>Once again refer to the PIC technote -- a fully functional speech
>synthesizer -- complete with schematic and source code. It might be
>just what you're looking for, as is. They even have PC based "C"
>software for creating the compressed image. All the work is done for
>you!

Well, hey, I haven't looked at that one yet. Cool! Anybody else have any
ideas?

I'd like to keep it cheap and easily assembled (common parts) to compete
with just bank-selecting more ROM from an old Speech board. (Judging from
the number of dead speech boards/missing SPO250's in the world though I can
imagine we'll need a replacement at some point.)

-Clay

Clayton N. Cowgill Engineering Manager
_______________________________________________________________________
/\ Diamond Multimedia Systems, Inc. clay@supra.com
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Received on Wed Dec 3 15:37:35 1997