From: grr@cbmvax.commodore.com (George Robbins)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: COMMODORE - HERE'S A CLUE
Date: 8 Oct 92 22:54:45 GMT
Reply-To: grr@cbmvax.commodore.com (George Robbins)
Organization: Commodore, West Chester, PA

In article <1992Oct8.152203.27725@murdoch.acc.Virginia.EDU> ccb8m@onyx.cs.Virginia.EDU (Charles C. Bundy) writes:
> grr@cbmvax.commodore.com (George Robbins) writes:
> 
> >In article <1992Oct5.180757.1@cc.helsinki.fi> jalkio@cc.helsinki.fi writes:
> >> In article <OA92-901-306p1_88E8203B@piraya.bad.se>, 
> >> Hans_Bergengren@p1.thulos.bbs.bad.se (Hans Bergengren) writes:
> >> > 
> >> >  GR> Not even Atari was dumb enough to try and create a custom chip that
> >> >  GR> did 16-bit audio, the job is much better given to a DSP to handle.
> >> > 
> >> > It's NOT! Suppose you want the DSP to do other stuff, like voice 
> >> > recognition, image enhancing, or 3D graphics, or any other of that 
> >> > nice stuff a DSP can do, why waste bandwidth on such a simple task 
> >> > as outputting audio?
> >> 
> >> Hey! As far as I have understood, the DSP is NOT needed for Audio output
> >> (even 16-bit stereo, or maybe 8-channels). There is a special
> >> audio-matrix-subsystem for that. You use the DSP, if you want some
> >> realtime audio processing.
> >
> >From the description of the "audio matrix" it sounds like some analog 
> >multiplexing of the audio signals.  This suggests that you can combine 
> >the DSP and the other on-board noisemakers in various clever ways, but 
> >the DSP is probably the only on that can generate 16-bit audio.
> >
> >It could be something better, but don't assume that something nice sounding
> >like and audio-maxtrix-subsystem offers more than offered by the basic 
> >on-board resources.
> >
> 
> I have one simple question to this ongoing thread :)  How on earth can a
> DSP "generate" any kind of audio?  Does it have an ADC?  Your bit limit
> range on sound comes from the ADC not the 56K DSP in the falcon.  The
> statement "16 bit sound can only be generated by the DSP" doesn't make
> sense in this context (unless you have a bunch of resistors hanging
> off it:)

DSP's usually provide a serial interface that can be used to provide a
bitstream to an audio DAC (CD style) or a CODEC (bi-directional A-D/D-A).

Somewhere in the Atari system, there is sitting a DAC or CODEC, which
we *might* assume is 16-bits and the DSP is probably directly interaced
to it.

There *might* be some other path that would let a DMA channel or CPU
port dump 16-bit samples directly to/from such a DAC or CODEC, which would
provide an alternative to the small sample memory of the DSP, but that is
not implicit in the specs that have shown up here.

What the specs do seem to imply is some kind of analog cross-point matrix
for selecting between the different audio function blocks provided.

This is not to say that the Atari implementation is "bad".  If there is
and efficient interface between the processor side and DSP memory (not
a given with many DSP's) that can let the processor or blitter use the
DSP memory as a buffer, then extensive sampling is possible.

If not, then the DSP still allows doing some pretty nice stuff with
either waveform synthesis techniques or doing expansion of ADPCM or
MPEG style compressed audio.
Newsgroups: comp.sys.amiga.advocacy