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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.

Daleks Exterminating!!!

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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Low Frequency Oscillator

Written by v on August 13, 2009 – 6:46 pm -

Many synths have a feature known as a Low Frequency Oscillator or LFO. The name is confusing, because usually, an oscillator refers something that makes a sound, like a square wave.

In this case the low frequency oscillator does not generate a sound, rather it is a control that is used to dynamically tweak or modulate  an existing sound to achieve different effects, making the sound more interesting.

It is called ‘low frequency’ because the frequency is usually at or just below the threshold of human hearing, usually less than 50hz, and often set to 20hz or 10hz.

Lets take a look at a few examples:

Imagine playing a note on your keyboard and turning the volume control knob rapidly back and forth with your fingers 10 times a second. By doing this, you are creating a tremolo effect. A 10hz LFO patched to the volume control would allow you to do the same thing without using your fingers.

Now imagine doing the same thing, but instead of turning the volume knob, you move the pitch bend wheel back and forth 10 times per second. This would create a vibrato effect. A 10hz LFO patched to the pitch bend control would do the same thing.

In fact, the LFO can be connected to a whole variety of controls or sound parameters to achieve different effects. The range of parameters you can control of course depends on the capabilities of your synth keyboard.

You can adjust the level (amplitude) of the LFO to determine whether you want a slight or a strong effect and you can raise or lower the frequency for faster or slower ‘throbbing’.

Digital Audio Workstation software and VSTs are usually extremely flexible in what you can control. In fact, you can use multiple LFOs running at different frequencies to control several parameters in parallel.


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