Everything about Ring Modulation totally explained
Ring modulation is a signal-processing effect in electronics, related to
amplitude modulation or
frequency mixing, performed by multiplying two signals, where one is typically a
sine-wave or another simple waveform. It is referred to as "ring" modulation because the
analog circuit of
diodes originally used to implement this technique took the shape of a ring. This circuit is similar to a
bridge rectifier, except that instead of the diodes facing "left" or "right", they go "clockwise" or "anti-clockwise".
Examples
These are some audio samples of the ring modulation effect:
Operation
Ring modulators combine (or
heterodyne) two
waveforms, and output the sum and difference of the frequencies present in each waveform. This process of ring modulation produces a signal rich in
overtones, suitable for producing bell-like or otherwise metallic sounds.
Two oscillators, whose frequencies were harmonically related and ring modulated against each other, produce sounds that still adhered to the overtones of the notes, but contain a very different spectral make up.
If the same signal is sent to both inputs of a ring modulator, the resultant harmonic spectrum is the original frequency domain doubled(If
,
and
. However, some distortion occurs due to the forward voltage drop of the diodes.
Some modern ring modulators are implemented using
digital signal processing techniques by simply multiplying the
time domain signals, producing a mathematically perfect signal output.
Multiplication in the
time domain is the same as
convolution in the
frequency domain, so the output waveform contains the sum and difference of the input frequencies. Thus, in the basic case where two sine waves of frequencies
and
(
) are multiplied, two new sine waves are created, with one at
and the other at
.
The two new waves are unlikely to be harmonically related and(in a well designed ring modulator) the original signals are not present. It is this that gives the ring modulator its unique tones.
Intermodulation products can be generated by carefully selecting and changing the
frequency of the two input
waveforms. If the signals are processed digitally, the frequency-domain convolution becomes
circular convolution. If the signals are
wideband, this will cause
aliasing distortion, so it's common to
oversample the operation or filter the signals prior to ring modulation.
Integrated circuit methods of ring modulation
On the
C64 SID chip, ring modulation multiplies a
triangle wave with a
square wave.
On an
ARP Odyssey synthesizer the ring modulator is an XOR function (formed from two NAND gates) fed from the square wave outputs of the two oscillators. Though not equivalent to ring modulation, with square waves the resulting sound is quite similar.
Use in music
Ring modulators are mostly used in
synthesizers and a ring modulator module was a common feature on early modular
Moog synthesizers. The ring modulator went out of fashion with the advent of all-in-one synthesizers and sampled-based synthesizers, but has returned as a feature in digital modelling and
software synthesizers.
It was a very commonly used effect in early electronic music, when analog oscillators were only capable of generating waveforms with a predictable series of overtones. One of the best-known applications of the ring modulator was its use by
Brian Hodgson of the
BBC Radiophonic Workshop to produce the distinctive voice of the
Daleks in the
television series Doctor Who.
A ring modulator effect is added to the guitar solo in the song "
Paranoid" by
Black Sabbath.
In one of the lineups during the 1970s electric period of
Miles Davis,
Chick Corea played a
Rhodes piano through a ring modulator. This gave the distinctive electric piano a very different and unusual sound. It can be seen and heard on a DVD release of Davis' performance at the Isle of Wight.
Early electronic composers, particularly
Stockhausen, used ring-modulator effects. Stockhausen's compositions
Kontakte (1958–60) and
Telemusik (1966) call for it and, indeed, whole compositions are based around it, such as
Mikrophonie II (1965, where the sounds of choral voices are modulated with a
Hammond organ),
Mantra (1970, where the sounds from two pianos are routed through ring modulators), and
Licht-Bilder from
Sonntag aus Licht (2002), which ring-modulates flute and trumpet.
Other applications
Ring modulation was also extensively used in old radio receivers. Ring modulators were used to demodulate the FM stereo signal. Examples include the HH Scott 310, 335, 345, 370B, and Fisher 500c.
Jon Lord from Deep Purple often used the Ring Modulator with his Hammond organ during live shows (Made in Japan, California Jam), and sometimes even in studio records (Rat Bat Blue).
Luke Vibert showcases the ring modulator sound in the "Fused into music", on his album, Big Soup.
Nicholas Briggs (voice of the
Daleks and the
Cybermen in the BBC science fiction series
Doctor Who) uses a Ring Modulator to alter his voice.
Further Information
Get more info on 'Ring Modulation'.
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