Introduction

Despite the enormous complexity and range of sound creation and processing devices available to the music maker, soundwaves have only three properties which can be manipulated ...

Pitch / frequency
Timbre / waveshape
Amplitude

Sound has no other properties, it doesn't have colour or taste or smell etc.

Most devices for manipulating sound fall into one of 4 categories ...

Synthesisers, which create electrical (or digital) soundwaves
Samplers, which playback and process pre-recorded digital sounds
Effects processors, which add additional harmonics into a soundwave
Dynamic processors, which control a soundwaves amplitude over time

Synthesis

Learning analogue (subtractive) synthesis is often thought to be the best way to understand sound manipulation. All the controls for creating and editing patches (sounds) on a synthesiser manipulate one or more of the folowing 3 sound properties, often changing them dynamically over time.

1. Altering pitch / frequency

Here are some ways in which the pitch of a soundwave may be manipulated ...

A singer controlling pitch with the muscles in their larynx
A pianist playing different notes on a keyboard
A guitarist moving their fingers up and down a fretboard or bending a string
A brass player operating the valves on their instrument
Pitch wheel on an electronic keyboard
A harmoniser processing a soundwave
An LFO sending a controlled voltage to modulate the pitch of an oscillator
A programmer setting the frequency of an oscillator
Time stretching in a digital wave editor

2. Altering timbre / waveshape

Every sound has a unique waveshape. This waveshape is derived from the combined energies of many individual harmonics, and determines the perceived character (timbre) of the sound. Here are some ways in which timbre may be altered ...

By passing a soundwave through a filter
By combining 2 or more soundwaves together to create a phase relationship between them
By applying EQ to the soundwaves
By editing the frequencies and amplitudes of the individual signals ("harmonics") which combine together to build an electrical (or digital) pressure soundwave in an oscillator (see FM or additive synthesis)
By processing a soundwave with an aural exciter

3. Altering amplitude

Here are some ways in which the amplitude of the individual harmonics within a complex soundwave, or the overall amplitude of a complex soundwave, may be manipulated ...

By turning an amplifier up and down by hand
By controlling an amplifier with an envelope
By controlling an amplifier with an LFO
By combining 2 or more waves together to create a phase relationship between them
By processing sound with a compressor
By processing sound with a noise gate
By altering velocity when playing an acoustic instrument