From: ladasky@netcom.com (John J. Ladasky II)
Subject: Re: Discussion on PC based Synthesizer/Sampler
Organization: Netcom - Online Communication Services (408 241-9760 guest)
Date: Mon, 14 Dec 1992 20:39:50 GMT

lieblm@Informatik.TU-Muenchen.DE (Martin Liebl) writes:
>
>
>Hi all you Computer/Music Freaks !
>
>With all this multimedia stuff being announced these days, I am carrying the
>idea of a PCM-synthesizer completely based on PC hard- and software, and would
>like to hear any opinions on this subject.
>
>Now here's my idea:
>Since today's synthesizers are (mostly) based on digital algorithms, it should
>be possible to realize such device completely based on a PC hardware with an
>additional D/A-converter (e.g. Soundblaster or similar card) and the software
>to compute the sound. 
>More exactly:
>I get some input from a connected midi keyboard (note on/off, aftertouch, etc.);
>I take some sample stuff (PCM) and transform it according to the midi input
>(pitch transpose, modulation, etc. ). Then I change it by several algorithms
>for filtering, envelope, etc. ; after doing this for all the played notes, I 
>merge the whole thing and send it out through a D/A-converter.
>If one can do this, I already have got a preset sampler like a U220 or a proteus.
>Extending it by algorithms for e.g. effect processing, waveshaping, 
>wavesequencing or whatever, one should be able to rebuild any kind of today's
>synthesizers; even FM should be possible with a different concept.
>Only the speed of the CPU decides, how many voices or different sound patches
>I can play simultaneously.
>I don't know if I'm right, but this is the same like Roland, Korg or Yamaha
>does it, the only difference is not using customized hardware; Peavey tried
>to sell their things on a similar 'open architecture' concept, but no one ever
>heard of new software for this.
>
>Now what would be the problem realizing this, or are there any projects on
>this ???
>The sound quality only depends on the DAC which converts it (besides the lack
>of analog filters or such stuff); but with a turtle beach card the output is
>CD like  (probably not with a Soundblaster).

	The sound quality of the DAC is not the only issue.  The digital 
environment in which the DAC operates will define a "noise floor."  The
typical PC is crammed so full of circuitry that was designed before good
grounding techniques were commonplace that much of the performance of a
16-bit linear DAC would be wasted.  You may be interested to know, however,
that an engineer who works with me says that _audio_quality_ ADC's and DAC's,
though they may have 16-bit output, are not generally specified to be linear
down to the least significant bit!  Some compromise in performance may 
therefore be audially acceptable - does anyone know how much?

	By the way, the subject line also mentions the possibility of
sampling, although the article does not discuss it.  The same issues would
be present with an ADC.  I would reccommend providing an externally-amplified
line-level signal to such a box, though.  A mic-level signal would be too
vulnerable to digital crosstalk if you performed the ADC right on the card.

	Does anyone know whether adequate shielding (i.e., a good metal can)
would help with the noise problem?

>How about the computer ?  Memory wouldn't be a problem, but how about the
>necessary CPU speed ? It certainly must be fast, but would a 486 be enough ???
>Do I need customized DSP's to get by ?

	You will certainly need DSP's to obtain any reasonable amount of 
computing power for real-time digital synthesis.  The microprocessors of
today's computers are not optimized for number-crunching, and presumably,
you would want to use that microprocessor to do the things a microprocessor
normally does (like run your operating system!).  As for memory, the 
_amount_ of memory would not be a problem, but the _location_ of that memory
certainly could be a problem.  I would reccommend placing a large block of
RAM right on the card containing the DSP chips, and connecting the DSP to 
the RAM with a high-speed bus.  The standard bus in PC-style computers is
too slow for fetching data from large numbers of wavetables in real time,
unless you want your DSP chips to waste a lot of time waiting.

>I would be delighted to hear some opinions from you!
>Be honest, we all are dreaming of a complete keyboarder's equipment 
>only consisting of a master keyboard and a laptop, and not spending $2000 for
>a device which does good pianos, another $2000 for one which is good for
>strings, etc. (and every 3 years throwing it all away because there are new
>modules with even better pianos, even better strings an so on)

	Yes, I'm dreaming about this too!  But if I had to do this
myself, I'd probably start with a bus architecture that is much faster
and less kludgy than the PC bus, and which has a reputation for being a
good bus for instrumentation.  VME/VXI comes to mind.  PC's are available
which reside on the VME bus, so we wouldn't have to throw away all our 
programming knowledge - but we could gain the advantage of a "real" bus.

	A laptop computer?  Say, now there's an idea...


-- 
== John J. Ladasky II ("ii") ========================= ladasky@netcom.COM ==
"Great composers do not borrow -	     "Talking about music is like
 they steal."  - John Ladasky	      ~ -     dancing about architecture."
(quote stolen from Stravinsky, who    o o     - Elvis Costello?  Laurie
 stole it from a statement made by     >        Anderson?  Frank Zappa?
 Pablo Picasso about painting, who    \_/    -------------------------------
 stole it from...)			     "Property is theft." - Groucho
============================================================================
Newsgroups: rec.music.makers.synth