17
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. Summit lets you adjust the duty cycle of the basic square waveform (via the Shape
controls) 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. Summit’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.
Frequency Modulation (FM)
Another method of combining the signals from two sources is Frequency Modulation,
or FM. In this technique, the frequency of one oscillator – sometimes referred to as
the “carrier” - is dynamically varied about its nominal “centre” value by an amount
corresponding to the instantaneous amplitude of the signal from the second oscillator.
Summit has a set of controls on the panel dedicated to adding FM effects.
The precise sonic result will depend on the wave shapes of each oscillator, their relative
pitch, and the maximum amplitude of the modulating signal: on Summit this latter parameter
may be controlled manually, and may be further varied by both LFO and Envelope.
The result of frequency modulation is the generation of a very wide range of additional
harmonics (in fact, theoretically infinite), both above and below the pitch of the oscillator
being modulated. In FM language, these harmonics are often referred to as sidebands.
The number of “significant” sidebands is proportional to the amplitude of the modulating
signal and inversely proportional to the frequency difference between the carrier and the
modulator. If the modulator is already rich in harmonics, e.g., something other than a simple
sine wave, each harmonic creates its own set of sidebands, further enriching the spectral
content of the result.
FM
MODULATOR
OSC 1
OSC 2
FREQUENCY
MODULATED OUTPUT
OSC 1 PITCH
Harmonics
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