PC Hardware in a Nutshell, Second Edition

MIDI Synthesis Methods

The process by which sounds cards produce audio output from MIDI input is called synthesis.

FM synthesis

FM synthesis combines multiple sine waves of differing frequency and amplitude to produce a composite wave that resembles the native waveform of the instrument being synthesized. How close that resemblance is depends on the instrument and the quality of the FM synthesizer circuitry, and may vary from reasonably close to only a distant approximation. Even the best FM synthesis sound cards produce artificial-sounding audio, particularly for “difficult” instruments. Until the mid 1990s, most consumer-grade sound cards used FM synthesis. Today, even the least expensive sound cards use better methods.

Wavetable synthesis

Wavetable synthesis uses stored waveform audio samples of actual instrument sounds to reproduce music. The sample may be used as is, or modified algorithmically to provide a sound for which no sample is stored. For example, the wavetable may contain a stored sample of an actual violin playing an A at 1760 Hz. If the MIDI score calls for a violin playing that A note, the sample is used directly. If the MIDI score calls for a violin playing an A note one octave higher (3520 Hz) and that note is not available as a stored sample, the synthesizer creates the 3520 Hz A note based on the data it has stored for the 1760 Hz A note. The quality of wavetable synthesis depends on the number, quality, recording frequency, and compression used for stored ...