Sound Synthesis Basics
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Blofeld User´s Manual
very symmetrical harmonic content, while all other pulse
widths create peaks or troughs at certain frequencies.
Another special case is a pulse wave with a very narrow
pulse width, in the above picture labelled as <1%. An
infinitely thin pulse creates a spectrum that has all
harmonics with equal magnitudes. In a digital synthesizer,
“infinitely” necessarily means one sample.
The pulse wave is an artificial wave, which means that it
doesn’t occur in nature. It was built into synthesizers
because it could create a lot of different timbres with a
minimum of technical effort. However, certain pulse
widths sound very close to the timbres of acoustic (or
semi-acoustic) instruments, i.e. a guitar or bass guitar, an
e-piano or even a flute.
The most powerful feature of the pulse wave is the ability
to change its width while sounding. This is called pulse
width modulation. When the pulse width is changed, the
waveform starts to sound thicker. This happens because
the effect is very similar to what you hear when you have
two oscillators running with slightly different frequencies.
They interfere and create irregular troughs in the resulting
waveforms.
The Triangle Wave
The Triangle Wave is very similar to the square wave. It is
composed of the same harmonics as the square wave, but
with different magnitude ratios. The magnitude of each
harmonic is divided by the power of its number. This
means that the third harmonic’s magnitude is a ninth, the
fifth harmonic is a twenty-fifth and so on. The following
illustration shows the harmonic content:
