From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.advocacy
Subject: Re: C= speaks!!! let's spread the words!!!
Date: 17 Aug 92 19:42:08 GMT
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Distribution: comp
Organization: Commodore, West Chester, PA

In article <nh5mcc@lynx.unm.edu> kholland@hydra.unm.edu (Kiernan Holland) writes:
>In article <34212@cbmvax.commodore.com> daveh@cbmvax.commodore.com (Dave Haynie) writes:

>>[the CD player has] two 16-bit channels (no volume control).  This is a big 

>Actually, the CD systems do. If you can possibly control the 65,556 
>amplitude levels that 16-bit DAC's generate.

Nope, sorry, that's no volume control.  Sure, the DAC data specifies particular
amplitudes, just like the DAC data on the Amiga does.  However, the Amiga's
channels have an independent volume control.  While you can't feed the volume
control from a DMA channel like you can the DAC, software that programs both
the DAC and the volume control on the Amiga directly with the CPU can get better
than 8-bit resolution on each channel.  Obviously a 16-bit DAC would work 
better than this, but the Amiga's channels are superior to the 8-bit CPU driven
D/A ports on the C64 or SoundBlaster.

>>compared to hardware synthesizers when you're playing pre-computed data,
>>such as samples.  With samples, you have an unlimited number of voices

>Well, you mean a variety different waveforms mixed together, not unlimited 
>voices. By your definition, I could say a organ has several thousand voices, 
>or would require several thousand oscillators to synthesize the correct harmonics.
>They become unlimited when you have a program that can mix 
>waveforms fast enough. 

Or when they're precomputer, as they are with a CD or a computer that's simply
playing samples, rather than synthesizing.  The number of independent waveforms
that can be played though a D/A channel is effectively unlimited, as the CD
player demonstrates (which is why I mentioned it in the first place).  The
number you can actually achieve depends on how the D/A data are generated.

>>If, instead, you're running some kind of audio synthesis program on the 
>>Amiga, the number of independent voices available is certainly based on how 
>>many can be synthesized and summed into each available channel in real time. 

>Correct. But you must have a really fast CPU to do it, and it doesn't always
>sound like a hardware implementation, if such 8-bit 8 voice DAC's 
>existed for the Amiga. It always sounds like 4 voices trying to 
>sound like 8 rather than 8 voices. 

If you have enough CPU time available, there's no way to tell whether the
voice mixing is done in the digital or analog domain, in software or in
hardware.  If you can hear the difference, you're either using poor software
or you don't have enough CPU time.  In reality, you really want a dedicated
processor (ideally a DSP) summing for you DAC, since it's an realtime
operation and the rest of your system's performance will suffer greatly if
the CPU's spending too much time doing sound synthesis.  The separate DAC 
channels on the Amiga with their corresponding DMA channels make D/As practical
on a system without too much CPU power.

>The AMiga doesn't even waste time on its 4 voices. 

Absolutely correct, though its the DMA channel that really makes that practical.
You could put four D/A channels on any system, but if the CPU has to fire off
data to each one at your chosen sampling rate, you're in trouble.  The 
synthesizer chips have always reduced this problem by requiring CPU intervention
only for waveform changes.  Still, to do fancy stuff, the CPU is pretty busy 
with these too.

>Acording to my calculations, you could simulate 14 bits of resolution (around 
>16 thousand amplitude levels). Or realistically (64*256)+1 amplitude levels.. 

Yeah, that's exactly what I talked about above.  The programmable volume control
is something you don't normally find in a D/A system.  It allows an extended 
audio range with some work.

>I can't see why anyone would want a Soundblaster Pro, unless they 
>really like Synthesized sound. 

I don't imagine folks buy these as alternatives to real keyboards or MIDI
based synthesizers.  They're just sound effects cards for PCs, so games
have good sound.  Anyone convincing themselves that Soundblasters, or 
Amigas for that matter, are equal to real instruments are just confused.
Then again, if you're interesting in learning about synthesis or just 
casually interested in music, the computer can make the mechanics more
accessible to non-musicians.
-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      BIX: hazy
	"Work like a horse, drink like a fish"	- Psychefunkapus
 
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