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Chapter 8 Modulation 101
RingShifter—Ring Modulator/Frequency Shifter
Logic’s RingShifter plug-in combines a ring modulator with a frequency shifter effect.
These two related effects are based on modulation of the signal amplitude. Both effects
were popular during the 1970’s, and are currently experiencing something of a
renaissance. The ring modulator, for example, was extensively used on jazz rock and
fusion records in the early 70’s. The frequency shifter was, and still is, found as part of
many modular synthesizer systems. Due to the intricate nature of its hardware, the
frequency shifter was (and remains) relatively expensive to produce, and was therefore
never as widespread as the simpler ring modulator.
Technical Background
The ring modulator modulates the amplitude of the audio input signal using either; the
internal oscillator or a second audio signal. The frequency spectrum of the resulting
effect signal equals the sum and difference of the frequency content of the two original
signals. Its sound is often described as metallic or clangorous.
An elaborate array of allpass filters enables the frequency shifter to separate the sum
and difference signals into two separate audio signals—one carries the audio signal
with its frequency spectrum shifted up, the other with its spectrum shifted down. The
amount of frequency shift is set via the frequency of the internal sine wave oscillator.
Frequency shifting should not be confused with pitch shifting. Pitch shifting transposes
the original signal, leaving its harmonic frequency relationship intact. The frequency
shifter shifts the frequency content by a fixed amount and, in doing so, alters the
frequency relationship of the original harmonics. The resulting sounds range between
sweet and spacious phasing effects to strange robotic timbres.