Theory of Operation:
Ring modulator (also known as product modulator or amplitude modulator) used to be one of the oldest traditional electronic musical instruments for so-called non-linear synthesis, although its technical concept is probably as old as broadcasting. "Non-linear" means hereby that some sounds are coming out, other than those which go in. Ring modulator owed its distinct sound to the combinational spectra it produced by multiplying instantaneous values of two audio signals, the carrier and the modulator. Modulator signal has usually been an audio line, carrier used to be a signal from the tone genetaror. As result signal, one would obtain a "combination tone" with both carrier and modulator frequencies supressed, but their spectral sums and differences synthesized. The spectrum of the result output signal would thus form a "ring" around what used to be the carrier frequency, i.e:
F(out) = F(fc + fm) + F(fc - fm)
where F stands for signal spectra, fc for instantaneous carrier frequency, fm for instantaneous modulator frequency. In other words, signal multiplication in time domain becomes convolution of frequency spectra.
History:
Ring modulator as musical device was invented in 1947 by Harald Bode, the legendary german inventor of so many marvelous early
signal processing devices, who in turn was inspired by the american guitarist and inventor Les Paul. Traditionally, it was manufactured in analog technology, using a
modulating amplifier (originally made of four diodes in ring-configuration) with two transformer-coupled inputs.
In order to make
any sound out of it, other than brutal and rough, extreme precision of tuning, intonation and pitch
control is required. Millivolt (or microtone) order of detuning gives radically different results. Due to the lack of
affordable high precision analog components and notorious temperature instability, controlling a ring modulator precisely was always an issue.
With the rise of digital
technology it went out of fashion, yet ring-modulator parts exist in
some of the finest scores of the classical era of electroacoustic
music. Few manufacturers build nowadays affordable ring modulator guitar pedals,
ring modulator software plug-ins can be found in the form of commercial software to be used within a virtual
recording studio or a plug-in host application, yet no live performance optimized, no-latency
application with exact and robust control of all musically important parameters had been around...
Design:
Even though ring modulator algorithm is one of the simplest DSP
algorithms one can think of, making a versatile musical instrument out of it involves few serious design
concerns. Yet, current digital technology offers precision of control unthought of in the "golden age" of
electronic music, without sacrificing its character of sound. RModX uses single audio-component design with instantaneous single-callback play-through mapping from input to output
port and amplitude modulation. All the controls and program options are real-time implemented
and single-window based.
