The Basics Of Fm Synthesis - Yamaha SY99 Owner's Manual

FM synthesis is a patented Yamaha method for using Frequency Modulation (FM) to produce complex
waveforms that can be controlled in musically useful ways.
Interesting sounds have
complex waveforms
FM is a simple way to
make a complex
waveform
Interesting sounds change
over time
56

The basics of FM synthesis

The sounds produced by most musical instruments have a very complex wave-
form, which is constantly changing.
Electronic instruments use an oscillator to produce a waveform. Unfor-
tunately, electronic oscillators are best at producing simple and repetitive
waveforms. These waveforms sound "artificial" or "electronic", and are not
very interesting to listen to. A major concern of electronic musical instrument
design is to find a simple way to electronically produce a complex waveform and
be able to control it.
The advantage of FM synthesis is that waveforms with very complicated
harmonic structure can be simply and economically created, and controlled in
many different musically useful ways. In FM synthesis, one waveform is used to
modulate another waveform. Even if the two original waveforms are simple, the
result can be a complex and interesting sound.
In the following diagram, the upper oscillator is called the Modulator and the
lower oscillator is called the Carrier. The complexity or brightness of the result-
ing waveform that we hear will depend on the output level of the Modulator; i.e.,
as we increase the modulation, the complexity or brightness will increase.
Increasing the output level of the Carrier will simply increase the volume.
Many instruments have a characteristic pattern with which the sound changes
as time goes by. This "shape in time" is called the envelope. The following dia-
gram shows how a piano envelope differs from an organ envelope. A piano
begins loud and then gradually diminishes in volume and tonal complexity. An
organ however maintains the same volume and tone as long as the key is
pressed.
Complex waveform
= interesting sound
Simple waveform
= boring sound