De Modules Notes

Harold Bode Quote[modifier]

Here is an excerpt from an old Electronic Music Review from Jan 1967 written by Harold Bode using diode ring and transformer "multiplier-type" ring modulator. Some nice examples of how this type ring modulator can be configured. Most interesting is Ex 8 where two ring modulator are configured to make a "tunable filter". Harold did use UTC brand A-20 transformers that had a wide frequency range in his ring modulators. I like the idea of this heterodyne effect of higher frequencies. Never tried this patch though?

Quote Harold Bode "Among all signal processors the multiplier-type ring modulator takes a unique position, since it is capable of converting existing sounds into new (and pleasing) sounds with entirely different overtone spectra that do not resemble the original acoustical phenomena. A few examples will illustrate some typical applications of this sound processing tool and the results obtained .

Ex. 1: A 1000 Hz sine wave is applied to the program input and a 900 Hz sine wave to the carrier input. The output contains two frequencies, 100 Hz and 1900 Hz. If the magnitudes of the inputs are both 1.0 volt RMS,the magnitude of the total output of the described standard model will also be 1.0 volt RMS. Ex. 2: The program input receives a 1000 Hz square wave and the carrier input receives a 900 Hz sine wave. A square wave contains an infinite series of discrete frequencies, all of which are odd multiples of the fundamental. The output therefore consists of two infinite series, one of which is the sum of the 1000 Hz square wave components and the 900 Hz sine wave, and the other of which is the difference. Ex. 3: Program input is filtered white noise with a bandwidth of 0 to 100 Hz and carrier input is a 900 Hz sine wave. This noise spectrum contains equal energy per unit bandwidth from 0 to 100 Hz. The output of the modulator is a spectrum centered at 900 Hz, but containing an equal distribution of frequencies from 800 Hz to 1000 Hz. Note that the bandwidth of the output is twice the bandwidth of the program input. When sweeping the carrier frequency of this setup over the center portion of the audio range, the sound of a howling wind may be simulated . A similar but more complex effect will be obtained when the program input is white noise with a bandwidth of, for instance, 400 to 500 Hz. In this case a carrier of 900 Hz would generate two white noise bands, one from 400 to 500 Hz and one from 1300 to 1400 Hz. Naturally, "tuned" white noise may cover a lesser bandwidth and thereby result in more selective effects. Ex. 4: The program material is supplied by a voltage-controlled oscillator which operates in the sine wave mode and is controlled by a keyboard. The carrier signal is supplied by a second voltage-controlled oscillator in the sine wave mode, controlled by the same keyboard and tuned relative to the first oscillator by a frequency ratio of 3:4, or any rational number. In case these integers do not have a common denominator, the resulting funda- mental frequency and its overtones at the output will be of a very attractive quality due to slow timbre changes, which may result from an intentional detuning of the two input frequencies relative to the theoretical multiples of the fundamental frequency. Ex. 5: Very interesting effects with the speaking or singing voice may also be obtained by feeding the fundamental voice frequency (obtained through a lowpass filter) into one input and the entire voice spectrum into the other. In this case the application of an efficient automatic gain control to the fundamental frequency (with the aid of a voltage-controlled amplifier) would be required, in order to retain the original dynamic properties of the input sounds. Ex. 6: When feeding the program material (preferably music and very effec- tively, organ music) into the carrier input and a low frequency sine wave in the vibrato range (for instance, 6 Hz) into the program input, a special modulation effect will be created, and will be remarkably enhanced if the same program material is reproduced directly (without modulation) through a second amplifier and speaker system . The result will be a kind of spatial amplitude-phase modulation . Ex. 7: Percussive sounds in the category of Trinidad drums are obtained when the sounds of bass drums, tom toms, temple blocks, wood blocks, claves, and maracas are fed into the program input and an audio frequency in the lower to middle audio range into the carrier input. Ex. 8: When the program material is heterodyned into a higher frequency range, say 10,000 to 20,000 Hz (with the aid of an oscillator of appropriate frequency feeding into the carrier input), and the new spectrum is passed through a narrow band filter in said frequency range, and the filtered fre - quencies heterodyned back into the audio range by applying the same oscillator frequency to the carrier input of a second ring modulator, the effect of a tunable filter is obtained when the oscillator frequency is changed .

From these examples, which merely scratch the surface of the possible appli- cations of the multiplier-type ring modulator, it will become evident that this instrument is a very powerful tool for the electronic music composer, and that the variety of results obtainable is as limitless as the imagination of the user."