Doepfer A-110 Standard VCO - Manual (Page 9)

doepfer System A - 100 VCO A-110
9
6. User examples
FM in the audio range
Using audio range oscillators for FM can produce
interesting sounds. Thanks to the rapid changes in the
modulated VCO’s pitch, side bands are created: as
well as the two original frequencies, you also get the
frequencies created by their sum and difference (for
instance, a modulation frequency of 100 Hz and a
carrier frequency of 500 Hz produce side bands at 400
Hz and 600 Hz).
Fig. 8: Frequency modulation in the audio range
When you try this out (see Fig. 8), start off with sine
waves, and slowly raise the modulation frequency from
the sub-audio into the audio range.
If you use waveforms other than sine waves in FM in
the audio range, the sounds that result will be extre-
mely complex and difficult to predict. A sawtooth, for
instance, can be looked upon as a vast number of sine
waves of different frequencies - all of which will be
represented in the modulated output, so that the final
sound will be a complex mix of the buzzes, noises and
tones produced by all the various sum and difference
outputs.
H The FM in the A-110 is exponential (as
opposed to linear) FM. This means that
changes in control voltage produce proportio-
nal changes in the pitch relationship of the
component sounds.
With FM in the audio range, this can lead to un-
desirable side-effects. If, for instance, a 440 Hz sine
wave is modulated by another with twice the amplitude,
the maximum frequency of the modulated signal will be
880 Hz, and the minimum will be 220 Hz (see Fig.9).
CV 1 Range
A-110
VCO
Tune CV 2
CV 2
Range
A-110
VCO
Tune