14
Sawtooth Waves
Sawtooth Wave
Volume
Harmonic
Square Wave
Volume
Harmonic
1 2 3 4 5
Volume
Harmonic
1 3 5 7
Triangle Wave
1 2 3 4 5
These are rich in harmonics, and contain both even and odd harmonics of the fundamental
frequency. The volume of each is inversely proportional to its position in the harmonic
series.
Square / Pulse Waves
Volume
Harmonic
1
Sine Wave
Sawtooth Wave
Volume
Volume
Harmonic
Square Wave
Volume
Harmonic
1 2 3 4 5
Volume
Harmonic
1 3 5 7
Triangle Wave
1 2 3 4 5
Harmonic
1 2 3 4 5
Noise
These contain only odd harmonics, which are at the same volume as the odd harmonics in a
sawtooth wave.
It will be noticed that the square waveform spends an equal amount of time in its ‘high’
state as in its ‘low’ state. This ratio is known as the ‘duty cycle’. A square wave always has
a duty cycle of 50% which means it is ‘high’ for half the cycle and ‘low’ for the other half.
Peak lets you adjust the duty cycle of the basic square waveform (via the Shape Amount
control) to produce a waveform which is more ‘rectangular’ in shape. These are often
known as Pulse waveforms. As the waveform becomes more and more rectangular, more
even harmonics are introduced and the waveform changes its character, becoming more
‘nasal’ sounding.
The width of the pulse waveform (the ‘Pulse Width’) can be altered dynamically by a
modulator, which results in the harmonic content of the waveform constantly changing. This
can give the waveform a very ‘fat’ quality when the pulse width is altered at a moderate rate.
A pulse waveform sounds the same whether the duty cycle is – for example – 40% or 60%,
since the waveform is just “inverted” and the harmonic content is exactly the same.
50%
40%
10%
60%
Noise
Noise is basically a random signal, and does not have a fundamental frequency (and
therefore has no pitch property). Noise contains all frequencies, and all are at the same
volume. Because it possesses no pitch, noise is often useful for creating sound effects and
percussion type sounds.
Volume
Harmonic
1
Sine Wave
Sawtooth Wave
Volume
Volume
Harmonic
Square Wave
Volume
Harmonic
1 2 3 4 5
Volume
Harmonic
1 3 5 7
Triangle Wave
1 2 3 4 5
Harmonic
1 2 3 4 5
Ring Modulation
A Ring Modulator is a sound generator that takes signals from two oscillators and
effectively “multiplies” them together. Peak’s Ring Modulator uses Oscillator 1 and
Oscillator 2 as inputs. The resulting output depends on the various frequencies and
harmonic content present in each of the two oscillator signals, and will consist of a series
of sum and difference frequencies as well as the frequencies present in the original signals.
The Mixer
To extend the range of sounds that may be produced, typical analogue synthesisers have
more than one Oscillator (Peak has three). By using multiple Oscillators to create a sound,
it is possible to achieve very interesting harmonic mixes. It is also possible to slightly
detune individual Oscillators against each other, which creates a very warm, ‘fat’ sound.
Peak’s Mixer allows you to create a sound consisting of the waveforms of Oscillators 1, 2
and 3, a Noise source and the Ring Modulator output, all mixed together as required.
OSC 1
OSC 1 VOLUME
OSC 2 VOLUME
OSC 3 VOLUME
COMPLEX
WAVEFORM
MIX OF
OSC1, 2, 3,
NOISE AND
RING
MODULATOR
MIXER
INPUT TO
FILTER
OSC 2
OSC 3
NOISE
RING MOD
NOISE
RING MOD
The Filter
Peak is a
subtractive
music synthesiser.
Subtractive
implies that part of the sound is
subtracted somewhere in the synthesis process.
The Oscillators provide the raw waveforms with plenty of harmonic content and the Filter
section subtracts some of the harmonics in a controlled manner.
There are three basic filter types, all of which are available in Peak: low-pass, band-pass
and high-pass. The type of filter most commonly used on synthesisers is low-pass. In a
low-pass filter, a “cut-off frequency” is chosen and any frequencies below this are passed,
while frequencies above are filtered out, or removed. The setting of the Filter Frequency
parameter dictates the point above which frequencies are removed. This process of
removing harmonics from the waveforms has the effect of changing the sound’s character
or timbre. When the Frequency parameter is at maximum, the filter is completely “open” and
no frequencies are removed from the raw Oscillator waveforms.
In practice, there is a gradual (rather than a sudden) reduction in the volume of the
harmonics above the cut-off point of a low-pass filter. How rapidly these harmonics reduce
in volume as frequency increases above the cut-off point is determined by the filter’s Slope
parameter. The slope is measured in ‘volume units per octave’. Since volume is measured in
decibels, this slope is usually quoted as so many decibels per octave
(dB/oct). The higher the number, the greater the rejection of harmonics above the cut-off
point, and the more pronounced the filtering effect. Peak’s filter section provides two
slopes, 12 dB/oct and 24 dB/oct.
A further important parameter of the filter is Resonance. Frequencies at the cut-off point
may be increased in volume by advancing the filter’s Resonance control. This is useful for
emphasising certain harmonics of the sound.
As Resonance is increased, a whistling-like quality will be introduced to the sound passing
through the filter. When set to very high levels, Resonance actually causes the filter to
self-oscillate whenever a signal is being passed through it. The resulting whistling tone
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