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8. Synthesis basics: Subtractive synthesis
Amplitude
10%
90%
Amplitude
50%
50%
In the first example, the jump happens 5% in from the beginning of the period. This is referred to as a
pulse wave with a 5% pulse width (sometimes called duty cycle). The second wave has a pulse width of
10%. The third wave has a pulse width of 50%. The third wave is a special case of the pulse wave, called
a square wave, and this has one peculiarity, it only contains odd number harmonics, which gives it a "hol-
low" quality.
On many synthesizers (including the Nord Modular) the pulse width can be adjusted, to set the timbre
of the pulse wave. The more narrow the pulse width, the "thinner" the sound will be.
You can also have the pulse width vary continuously, for example from an LFO or envelope. This is re-
ferred to as pulse width modulation (PWM). Modulating pulse widths from an LFO creates a rich, chorus-
like effect often used in "string" sounds.
A A A A
B B B B O O O O U U U U T T T T I I I I N N N N H H H H A A A A R R R R M M M M O O O O N N N N I I I I C C C C S S S S P P P P E E E E C C C C T T T T R R R R A A A A
Above we have only discussed spectra where the overtones appear at perfect harmonics. While this is true
for the basic waveforms discussed above, it is definitely not true for all sounds. If you for example use the
various frequency modulation (FM) or ring modulation capabilities in the Nord Modular, with two os-
cillators set to an "unusual" interval (not octaves or fifths, for example), you will get a spectrum where
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Amplitude
Time
Amplitude
Time
NORD MODULAR V3.0
10
20
30
40
10
20
30
40
Harmonic number
(Frequency)
Harmonic number
(Frequency)
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