Yamaha TX81Z Product Manual page 85

What's FM?
DETUNE
SCALING
LEARNING FM
SYNTHESIS
The harmonic structure of actual acoustic sounds is usually somewhat
"irregular". This makes them sound interesting and lifelike. By slightly De-
tuning each operator, you can create this type of naturally irregular harmonic
structure.
The tonal characteristics of an instrument generally change from note to note.
For example, high notes on a piano have a simpler harmonic structure than the
bass notes. By Scaling the output level of a modulator to decrease as you play
up the keyboard, you can simulate this. High notes on many instruments
also have a shorter envelope. You can simulate this by using Rate Scaling.
It is rather time-consuming to create a voice from the initial setting, since you
would have to set most (or all) of the 92 parameters that make up each voice.
The best way to learn is to get inside the factory preset voices and see how they
work. Turn each operator off one by one, and see how each operator affects
the sound. Make small changes in operator output level or EG rates. Try
starting from a preset voice that is fairly close to what you have in mind, and
edit it to your liking.
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