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Chapter 22 ES2 239
A ring modulator has two inputs. At it’s output you will find the sum and difference
frequencies of the input signals.
The graphic shows the output signal of the ring modulator, appearing as the output
signal of Oscillator 2. The amplitude (or the elongation, to be more exact) of the output
of Oscillator 2 changes with the phase of Oscillator 1. Oscillator 2 is set to a higher
frequency than Oscillator 1. As the frequency ratio is odd (irrational), the resulting
waveform always changes over time. The resulting spectrum is inharmonic and you
won’t hear a clearly defined pitch.
If you ring-modulate a sine oscillation of 200 Hz with a sine oscillation of 500 Hz, the
output signal of the ring modulator will consist of a 700 Hz (sum) and a 300 Hz
(difference) signal. Negative frequencies result in a change of the phase polarity of the
output signals. With sawtooth and rectangular input signals, the output signal is much
more complex, as these harmonically-rich waveforms produce a number of extra side
bands.
Note: Ring modulation is a powerful tool for inharmonic, metallic sounds as the spectra
resulting from its use are inharmonic with almost every frequency ratio. The ring
modulator was the tool of choice for bell-like sounds, and dates back to the early days
of the synthesizer (see the “RingShifter—Ring Modulator/Frequency Shifter” section, on
page 101).