Waldorf Rocket - Manual (Page 28)

Sound Synthesis Basics
Rocket User´s Manual 28
Additive components of Pulse wave with different pulse
widths
The first fact you can probably observe is that the lower
part of the wave has a narrower excursion. This is becau-
se the energy of the wider pulse is higher than the one of
the narrower pulse. If this were not compensated, the
overall signal would have an unwanted DC offset.
As you have read in the previous chapter, the harmonic
content of a 50% pulse wave is a special case. It has a
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 har-
monics 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 can 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.
1 3 5 7 9 11 13 15
1 3 5 7 9 11 13 15
1 3 5 7 9 11 13 15
1 3 5 7 9 11 13 15
50% Pulse
(Square Wave)
25% Pulse
<1% Pulse
(Impulse)
33% Pulse