[sdiy] questions on string synthesizers

[Adrian Corston]

I think they are essentially the same as old organs - the basic
approach is to generate a square wave for each note, then optionally
use a fixed filter (often just a resistor and a capacitor/inductor) to
produce various different tones, then optionally combine those tones
for each key to produce different timbres.  The details of how this
is done (which is what you're actually asking about) varies from
machine to machine - older designs used multiple poles on the key
switches to allow the tones to be combined; newer designs used note
keying chips which did the combining internally.  There are almost
certainly other techniques I don't know about.

Many stringers also had effects such as phaser circuits, BBD-based
chorus, and vibrato (achieved by varying the clock on the top octave
generators) to produce the classic "string machine" sound.

Fun fact: some organs produced white noise for their drum machines by
combining many unrelated (dissonant) tones (somewhat like the
TR606/DR-110 cymbal sound that was generated by combining 6 square
wave oscillators).

The one thing I haven't been able to fully understand is how they did
fully polyphonic A/R envelopes.  I've been meaning to have a look at
some schematics at some stage but haven't gotten around to it yet.

Cheers,
A.

----- Original Message -----
From: "Elain Klopke" <functionofform at gmail.com>
To:<synth-diy at synth-diy.org>
Cc:
Sent:Sun, 19 Feb 2017 15:31:17 -0600
Subject:[sdiy] questions on string synthesizers

How do the selectors for the various sounds work? Like with the violin
and cello, trumpet and tuba tabs or stops, you press the button and
you hear an aproximation of a violin sound, and you can add in the
rest of the sounds to get something orchestral. How is the string
synth taking the raw output from the top octive chip and subsequent
dividers and transforming it into the various instrument sounds? I
assume there's some sort of filtering going on, but I can't quite wrap
my head around it.

thanks,

-Ian
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