Design your own waveform synths?

[Jerry Federspiel]

At 01:31 AM 2/25/1999 -0800, you wrote:
>This may be a topic more appropriate for DH, but haven't
>there been some music machines built that allow you to
>design your own waveform right on a monitor screen?  I've
>often been interested in what the tonal properties would be
>like for a waveform, say, sine on the upramp, and square on
>the return to zero.  Or maybe an ascending sawtooth on the
>first 50% with a descending sine on the last half.  Since
>analogs are limited in this area, I've never been able to
>experiment to find out for myself.

Actually, to do this you can do one of at least two things.  One, download
a program called "Smorphi".  It allows you to draw your own waveforms and
play around with them.  Two, a program called "Goldwave" allows you to
directly edit the samples that make up a .wav file.  Just make a tiny .wav
file (like 100 samples), direct-edit the waveform to your heart's content,
and then copy and paste the waveform many many times.  Play back the
waveform and voila!  (I only suggest this method because Goldwave is such a
great all-around editor that you should download it anyway).  Additionally,
you could make specific hardware (described below) to synthesize any of the
waveforms you mentioned.

If you don't want to do either of these, I can prepare the sounds you
specifically requested and send them to you.

>Anyway, how come the idea isn't more popular with
>synthesists?  Is this something that would HAVE to be
>digitally controlled?  Couldn't an analog be built that
>could do it with precision voltage control?

Actually, the specific waveforms you mentioned could be done in analog;
they were each pieced together from existing analog waveforms.  To do a
waveform that is pieced together from existing analog waveforms, generate
the waveforms that the sound is pieced together from.  For each such
waveform, generate a rectangle wave that is offset so that its lowest
voltage is zero, and its highest voltage is "on" for the times that you
wish that particular waveform to be present in the final waveform.
Multiply each of the original waveforms with its corresponding rectangle
wave.  Then, sum all of the multiplied signals together.  The result will
be a pieced-together waveform, done entirely in analog.  Unfortunately, the
waveform will not be as controllable as you wanted it to be; the circuits
to generate that would generate only that specific pieced-together wave.

Caveats:
This approach was dreamed up by someone who has done all of his work in the
digital domain, and so the effects of using analog circuits to reproduce
this process will probably inject unwanted results.  For example, if the
rectangle waves are not perfectly synchronized, expect spikes in your
output as the "on" portions of more than one rectangle wave overlap.

As a semi-related side note, the sounds produced by non-synchronized
ring-modulating rectangles with the above technique are WAY cooler (warmer,
actually) than perfectly synchronized ones- just keep the levels low enough
so that it doesn't matter if all of the constituent waves are "on" at the
same time.  However, on the downside, such a waveform doesn't make a very
precise control signal...

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