Sound Parameters – Oscillators
69
Waldorf Q User’s Manual
The Pulse Wave
The Pulse Wave is the most versatile wave in a classic synthesizer because its shape and therefore its
harmonic content can be changed in realtime. This is done by changing the width of the upper and
lower portion of the waveform cycle. These portions are called pulses, hence the name pulse width.
The width of the first pulse is used to distinguish between different pulse waves and it is measured in
percent. The following picture shows several pulse waves with different pulse widths:
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
Picture 13:
Additive components of Pulse wave with different pulse widths
The first thing you probably note is that the lower part of the wave gets closer to the center. This is
because the energy of the wider pulse is higher than the one of the narrower pulse. If this wouldn’t be
compensated in the waveform, the overall signal would have an unwanted DC offset.
As you could 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 holes at
certain frequencies. Another special case is a pulse wave with a very narrow pulse width, in the
above picture labelled with <1%. An infinitely thin pulse creates a spectrum that has all harmonics
with equal magnitudes. In a digital synthesizer, “infinitely” for sure 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 to change its pulse width during a sound. 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 would get when you have two
oscillators running with slightly different frequencies. They interfere and create irregular holes in the
resulting waveforms.
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