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Additive Harmonic Synthesis

Now there's a formidable title. Just saying the three words together a few times implies complex and esoteric theory. There is nothing new about this system, by the way. It was already in use in a limited form in the pipe organs of 16th century Europe.

Rather than repeat what I've already written in other articles, I would refer you to the sections in the Hammond Article that deal with the method by which traditional Hammonds create multitudes of different tonal effects, because that is what additive harmonic synthesis is. These are two links to relevant sections of that material: page5 and page 11.

Additive harmonic synthesis would really be a great system, except that using the technology available at the time would have resulted in an extremely complicated and expensive instrument, and so there are several serious compromises, among the most prominent of which are that only a very limited number of harmonics are available and also that all of the upper harmonic pitches are derived from the equally tempered scale. Therefore, with the exceptions of harmonics which are exact octave intervals above the fundamental or basic pitch, all of the others are not exact whole number multiples of the fundamental frequency because they are derived from the tempered scale.

Nevertheless, additive harmonic synthesis has many good features. It yields a lot of different tone colors, just about all of which sound good. Because the upper harmonics are derived from the tempered scale, playing chords produces no interference beats between various harmonics. You might actually call the effects developed by additive harmonic synthesis ear candy. To further this gustatory analogy, we could say that this system yields nothing but highly palatable, sugar-coated tonal effects; one of the reasons for the great success of the Hammond and certain other electronic organs which also utilized this system. It's really hard to make unpleasant sounds on such an instrument.

The Formant System

This is the other system used by electronic organs to make various tonal effects. Because I have not covered the formant system in the previous articles, I will devote a little more space to this system.