Subtractive synthesis is a method of
sound synthesis in which
partials of an audio signal (often one rich in
harmonic
A harmonic is a wave with a frequency that is a positive integer multiple of the ''fundamental frequency'', the frequency of the original periodic signal, such as a sinusoidal wave. The original signal is also called the ''1st harmonic'', the ...
s) are attenuated by a
filter to alter the
timbre of the sound. While subtractive synthesis can be applied to any source audio signal, the sound most commonly associated with the technique is that of
analog synthesizers of the 1960s and 1970s, in which the harmonics of simple waveforms such as
sawtooth,
pulse or
square wave
A square wave is a non-sinusoidal periodic waveform in which the amplitude alternates at a steady frequency between fixed minimum and maximum values, with the same duration at minimum and maximum. In an ideal square wave, the transitions b ...
s are attenuated with a
voltage-controlled resonant
low-pass filter. Many
digital
Digital usually refers to something using discrete digits, often binary digits.
Technology and computing Hardware
*Digital electronics, electronic circuits which operate using digital signals
**Digital camera, which captures and stores digital i ...
,
virtual analog and
software synthesizers use subtractive synthesis, sometimes in conjunction with other methods of sound synthesis.
Examples of subtractive synthesis
The following is an example of subtractive synthesis as it might occur in an electronic instrument. It was created with a
personal computer program designed to emulate an analogue subtractive synthesizer. This example will attempt to imitate the sound of a plucked string.
''Whilst the following example illustrates how a desired sound might be achieved in practice, only the final three stages are really subtractive synthesis, and the early stages could be considered to be a form of
additive synthesis
Additive synthesis is a sound synthesis technique that creates timbre by adding sine waves together.
The timbre of musical instruments can be considered in the light of Fourier series, Fourier theory to consist of multiple harmonic or inharmoni ...
.''
First, two oscillators produce relatively complex and harmonic-rich waveforms:
Pulse-width modulation
Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a method of reducing the average power delivered by an electrical signal, by effectively chopping it up into discrete parts. The average value of voltage (and current) fed ...
is added for a dynamically changing tone:
The two sounds are mixed. In this case they are combined at equal volume, but any ratio could be used.
The combined wave is passed through a
voltage-controlled amplifier connected to an
attack, decay, sustain and release envelope. In other words, its volume is changed according to a pre-set pattern. This is an attempt to emulate the envelope of a plucked string:
Then pass the sound through a shallow
low-pass filter:
In this case, to better emulate the sound of a plucked string, the filter cutoff frequency should start in the mid-range and to low. The effect is similar to an electric guitar's
wah pedal.
In real music production, there is often an additional step. An oscillator with a very
low frequency
Low frequency (LF) is the ITU designation for radio frequencies (RF) in the range of 30–300 kHz. Since its wavelengths range from 10–1 km, respectively, it is also known as the kilometre band or kilometre wave.
LF radio waves exh ...
modulates one or more sounds over time, creating a dynamically changing sound.
See also
*
Additive synthesis
Additive synthesis is a sound synthesis technique that creates timbre by adding sine waves together.
The timbre of musical instruments can be considered in the light of Fourier series, Fourier theory to consist of multiple harmonic or inharmoni ...
*
Minimoog
The Minimoog is an analog synthesizer first manufactured by Moog Music between 1970 and 1981. Designed as a more affordable, portable version of the modular Moog synthesizer, it was the first synthesizer sold in retail stores. It was first popul ...
*
MicroKorg
*
Modular synthesizer
Modular synthesizers are synthesizers composed of separate modules for different functions. The modules can be connected together by the user to create a patch. The outputs from the modules may include audio signals, analog control voltages, o ...
*
Korg MS-20
*
Novachord
*
Steiner-Parker Synthacon
References
External links
AMS– A free software synthesis program for
ALSA.
{{Sound synthesis types
Sound synthesis types
ru:Субтрактивный синтез