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What is Ring Modulation?

Written by v on August 13, 2009 – 8:31 pm -

Ring modulation is an effect  that was introduced in the first analogue subtractive synths. Basically, it involves multiplying two waveforms together, e.g. multiplying a triangle wave and a square wave, to produce a new waveform that was the product of the inputs.

Electronically, this was a simple technique to create a new more complicated sound without requiring new waveform generator circuits.  The resultant waveform would have different harmonics to either of the original inputs and could then be filtered by the musician to create a new sound.

It is called ring modulation because one of the electronic circuits that implemented this operation used 4 diodes connected together in a ring-like configuration, similar to a bridge rectifier.

One of the most famous uses of ring modulation was to create the voice of the evil robots, the Daleks, in the British science fiction TV series Dr Who. The voice actor’s voice was ring-modulated with a 300hz sine wave and then filtered to produce the characteristic warbling sound.

Also, the MOS-6581 (SID) sound chip used in the Commodore 64 home computer implemented a limited form of ring modulation – one of the inputs to the ring modulator was always a square wave.

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