Archive of the former Yahoo!Groups mailing list: MOTM

previous by date index next by date
  topic list  

Subject: FW: [AH] Frequency doubling for VCOs

From: "Dave Bradley" <daveb@...>
Date: 2000-07-28

(Amazing - a nice programming trick amidst the dreck that is usual to AH -

Frequency Doubling for VCOs

Here's an idea to create a sound one octave above the normal pitch. Maybe
it will help us focus on analog stuff...

We all know you can get sub-octaves by putting flip-flops after the VCO
One pulse sets the FF output to high, the next pulse switches the output to
low, and so on.

You cannot use this technique to get higher than original sounds simply
because you don't know when the next pulse is due.
Or do you?

If you take an ascending (for now) sawtooth, you can use a CPR
(comparator) module to get a square wave. The second half of the wave will
yield a positive output.

If you invert that pulse-out, and add it to a the sawtooth output (after
the CPR), you get two rising ramps for every VCO cycle.

If you adjust the levels so that these two ramps are identical, you have
created a sawtooth wave one octave above the VCO's pitch.

Better still: If you still have modules to spare you can repeat this trick
for more octaves!

Have fun!