Basic Theory
Earlier in this manual we were introduced to the basics of subtractive synthesis & became familiar with terms such as harmonics,
timbre, waveforms & oscillators. FM Synthesis is the technique of using one waveform ( Oscillator ) to Frequency Modulate - FM -
another to produce a resultant more harmonically complex waveform.
For purposes of illustration we will assume that the oscillators are producing sine waves.
As we have already discovered it is the CHANGE in harmonics over time that starts to make a sound interesting to our ears. In FM
synthesis an envelope generator is inserted between the modulator & carrier waveforms so we have control over of how much
Frequency modulation is taking place with respect to time.
Adding this envelope makes the basic FM building block look like this
We can see that the output waveform starts off as the same as the carrier, becomes more complex (HARMONICS ARE ADDED)
as the amount of FM modulation increases via the envelope, & then returns to a simple wave again as the envelope decays. THE
TIMBRE OF THE WAVEFORM IS CHANGING WITH TIME. This is the opposite of subtractive synthesis where often a LOW PASS
FILTER is used to REMOVE HARMONICS.
To complete this simple synthesizer we need to add one further envelope to control the volume of what we are hearing. The com-
plete building block will now look like this.
Yamaha popularised FM synthesis in the 1980’s with the famous DX7 synthesiser.The basic building block of the original Yamaha
machine was referred to as an OPERATOR. An operator is just one oscillator with one envelope generator that can control the out-
put level of the Oscillator.
Modulator
Env - used to
control FM
modulation
amount
Env - used to
control amplitude
of sound over
time
Carrier
Output
Osc 1- Modulator
Osc 3- Carrier
Output Waveform
Envelope
modulation
level = 20
Osc 1- Modulator
Osc 3- Carrier
Output Waveform
Modulation level = 0
= 30
= 90
ABOUT FM SYNTHESIS
15
Summary of Contents for Supernova II
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