[sdiy] VCO Linear Voltage

[Jerry Gray-Eskue]

A very important point from a musical sense.

JH. also mentioned this one.

- Jerry

-----Original Message-----
From: Florian Anwander [mailto:fanwander at mnet-online.de]
Sent: Tuesday, November 17, 2009 10:18 AM
To: Jerry Gray-Eskue
Cc: Synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] VCO Linear Voltage


Hi Jerry

> but I still do
> not get why it would be better for audio FM patches.
With linear modulation the the average frequency (right word?) of the 
frequency modulated carrier will stay the same as the original frequency 
of the carrier. With exponential modulation, the average frequency 
differs from the original frequency.

Its quite simple if you imagine a symetric rectangle wave as modulation 
source. Assume the original frequency of the carrier is 400 Hz, so a 
rectangle with 2V full amount will modulate 1 V up and 1 V down. With 
linear FM (lets assume 1 Volt = 200Hz) the resulting frequencies are 
200Hz and 600Hz, the average is 400Hz again. With exponential modulation 
(1V=1Octave) the resulting frequencies will be 200Hz (one octave down 
from 400Hz) for the down modulation and 800Hz (one octave up from 400Hz) 
for the up modulation. The resulting average frequency will be 600Hz 
instead of 400Hz.

For my book I made a detailed graphic for exactly this example. I'll 
have a look to find it at home.

Florian