About Analogue Synthesis - Novation SuperNova II User Manual

ABOUT ANALOGUE SYNTHESIS

OSCILLATORS - pitch
To understand synthesis, it is necessary to have some understanding about sound itself. Sound is a vibration or oscillation. These
vibrations create changes in air pressure which is picked up by your ears & is perceived as sound. When dealing with musical
sounds the vibrations or oscillations occur at regular intervals & are perceived as the "Pitch" or "Frequency" of a sound. The sim-
plest musical sound is a sine wave because it contains only one "Pitch" & is perceived as a very "Pure" tone similar to a whistle.
Most musical sounds consist of several different "Pitches" or "Frequencies". The loudest is referred to as the "Fundamental" &
determines the perceived "Pitch" of the note. The other frequencies present are called "Harmonics" & in musical sounds usually
occur in multiples of the fundamental frequency. i.e. if the fundamental note is 440Hz then a musical harmonic series would be 2nd
harmonic = 880Hz, 3rd harmonic = 1320Hz, 4th harmonic = 1760Hz, 5th harmonic = 2200hz etc. The number & loudness of these
"Harmonics" determines the "Timbre" of a sound. This gives a sound character & is why a violin sounds different from a guitar & a
piano sounds different again. In an Analogue synthesiser, you have the choice of several different waveforms. Each waveform has
different amounts of harmonics & so the "Timbre" of each one is quite different. Below are descriptions of some of the waveforms &
indications on what they can be best used for.
Sawtooth waves have all the harmonics of the fundamental frequency. As you can see, every harmonic has half the amplitude of
the previous one. This sound is pleasing to the ear & is useful for basses, leads, & synthesising stringed instruments.
Square waves have only the odd harmonics present. These are at the same amplitudes as the odd harmonics in a saw wave.
Square waves have a hollow / metallic sound to them & so are useful in creating unusual synthesiser sounds & oboe like sounds.
White noise has no fundamental & all harmonics are the same value. This wave can be used by itself to synthesise explosions or
wind & when used in conjunction with other waveforms can be used to create the illusion of "Breath" in an instrument.
PWM ( PULSE WIDTH MODULATION )
The choice of waveform is important as it determines the basic "Timbre" of the sound you are making. There are additional meth-
ods of synthesis that allow more harmonics to be generated. The First of these is Pulse Width Modulation. ( PWM for short ).
Essentially the duty cycle of the normally symmetrical square wave is varied. This means the wave form goes from a Square wave
to a Pulse wave like so:
Square Waveform
This has a very pleasant "thickening" chorus like effect & is often used in Pad type & String section type sounds.
Saw Waveform
Square Waveform
Noise Waveform
Level
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Harmonics
Level
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Harmonics
Level
1 2 3 4 5 6 7
Harmonics
Variable Width
Pulse Waveform
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