Subtractive synthesis is a method of subtracting harmonic content from a sound via sound synthesis, characterised by the application of an audio filter to an audio signal. For example, taking the output of a sawtooth generator and using a low-pass filter to dampen its higher partials generates a more natural approximation of a bowed string instrument than using a sawtooth generator alone. Typically, the complexity of the source signal and the cut-off frequency and resonance of the filter are controlled in order to simulate the natural timbre of a given instrument. This article is about the components of sound. ... The term synthesiser is also used to mean frequency synthesiser, an electronic system found in communications. ... An audio filter is a type of filter used for processing sound signals. ... This article or section does not cite its references or sources. ... A low-pass filter is a filter that passes low frequencies but attenuates (or reduces) frequencies higher than the cutoff frequency. ... jake faulkner is partially retarded. ... A string instrument (or stringed instrument) is a musical instrument that produces sound by means of vibrating strings. ... In telecommunications, the term cutoff frequency fc has the following meanings: 1. ... In music, timbre, or sometimes timber, (from Fr. ...

Subtractive synthesis is historically associated with analogue voltage controlled synthesisers such as the Moog synthesizer due to the simple circuitry required to generate the most common source signals: square waves, pulse waves, sawtooth waves and triangle waves. Modern digital and software synthesisers may include other, more complex waveforms or allow the user to upload arbitrary waveforms. Some synthesisers may use a form of pulse width modulation which dynamically alters the source for a richer, more interesting, more organic tone. The term synthesiser is also used to mean frequency synthesiser, an electronic system found in communications. ... The term Moog(pronounced // as in moan) synthesizer can refer to any number of analog synthesizers designed by Dr. Robert Moog or manufactured by Moog Music, and is commonly used as a generic term for analog and digital music synthesisers. ... A square wave is a kind of basic waveform. ... In signal processing, the term pulse has the following meanings: A rapid, transient change in the amplitude of a signal from a baseline value to a higher or lower value, followed by a rapid return to the baseline value. ... The sawtooth wave is a kind of basic waveform. ... A triangle wave is a waveform named for its triangular shape. ... For other uses, see Digital (disambiguation). ... Computer software (or simply software) refers to one or more computer programs and data held in the storage of a computer for some purpose. ... Pulse-width modulation of a signal or power source involves the modulation of its duty cycle to either convey information over a communications channel or control the amount of power sent to a load. ...

Examples of subtractive synthesis

A human example

An easy and familiar way to understand the basis of subtractive synthesis is to consider our own personal "synthesiser" - when we speak, sing or make other vocal noises the vocal folds act as an "oscillator" and the mouth (and throat) as the "filter". Consider the difference between saying or singing "oooh" and "aaah" (at the same pitch.) The vocal folds are generating pretty much the same raw sound in either case - a sound which is rich in harmonics. The difference between the two comes from the filtering which we apply with the mouth and throat. By changing the shape of the mouth, we vary the "cutoff frequency" of the filter, so removing (subtracting) some of the harmonics. The "aaah" sound has most of the original harmonics still present, the "oooh" sound has most of them removed (or to be more precise, reduced in amplitude.) By gradually changing from "oooh" to "aaah" and back again, you can simulate the "sweeping filter" effect which is widely used in electronic music and which is the basis of the "wahwah" guitar effect (which is so named for its similarity to this vocal "filter.") // Bold textItalic text The vocal folds, also known popularly as vocal cords, are composed of twin infoldings of mucous membrane stretched horizontally across the larynx. ... Oscillation is the periodic variation, typically in time, of some measure as seen, for example, in a swinging pendulum. ... An audio filter is a type of filter used for processing sound signals. ... Pitch is the perceived fundamental frequency of a sound. ... In acoustics and telecommunication, the harmonic of a wave is a component frequency of the signal that is an integral multiple of the fundamental frequency. ... A bode plot of the Butterworth filters frequency response, with corner frequency labeled. ... For quantum-mechanical amplitude, see probability amplitude. ... For other uses, see Electronic music (disambiguation). ... Wah-wah is an imitative word for the sound of bending or altering musical notes to improve expressiveness, sounding much like a human voice saying the syllable wah for each note. ...

We are also capable of generating something approximating white noise with the mouth by making a "sshh" sound. If you "synthesise" a "jet plane landing" sound you are doing so mostly by using the shape of your mouth to filter the white noise into pink noise by removing the higher frequencies. The same technique (filtered white noise) can be used to electronically synthesise the sound of ocean waves and wind, and was used in early drum machines to create snare drum and other percussion sounds. Calculated spectrum of a generated approximation of white noise White noise is a random signal (or process) with a flat power spectral density. ... Pink noise spectrum Pink noise ( ), also known as 1/f noise or flicker noise, is a signal or process with a frequency spectrum such that the power spectral density is proportional to the reciprocal of the frequency. ... A Boss DR-202 Drum Machine Drum machines are sequencers with a synthesizer, sampler, and/or a sample playback (rompler) component that is tailored to imitate the sounds of drums and other percussion instruments. ... The snare drum or side drum is a tubular drum made of wood or metal with skins, or heads, stretched over the top and bottom openings, and with a set of snares (cords) stretched across the bottom head. ... Percussion redirects here. ...

An electronic example

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 synthesiser. We will attempt to imitate the sound of a plucked string.

Whilst the following example illustrates how a desired sound might be achieved in practise, 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 technique of audio synthesis which creates musical timbre. ...

1. First, two oscillators produce relatively complex and harmonic-rich waveforms:
   • Waveform #1 (help·info)
   • Waveform #2 (help·info)
2. In this case we will use pulse-width modulation for a dynamically changing tone:
   • PWM waveform #1 (help·info)
   • PWM waveform #2 (help·info)
3. The two sounds are mixed. In this case they are combined at equal volume, but any ratio could be used.
   • Combined waveforms (help·info)
4. The combined wave is passed through a voltage controlled amplifier connected to an ADSR envelope. In plain language, it is changed according to a pre-set pattern. In this case we attempt to emulate the envelope of a plucked string:
   • Enveloped sound (help·info)
5. We then pass the sound through a shallow low-pass filter:
   • Low-passed sound (help·info)
6. In this case, to better emulate the sound of a plucked string, we want the filter cutoff frequency to start in the mid-range and move low. The effect is similar to an electric guitar's wah pedal.
   • Final sound (help·info)
   • Some arpeggios (help·info)
   • A patriotic tune (help·info)

In real music production, there is often an additional step. An oscillator with a very low frequency modulates one or more sounds over time, creating a dynamically changing sound. This example modulates the cutoff frequency of the filter over several bars of music: An example of PWM: the supply voltage (blue) modulated as a series of pulses results in a sine-like flux density waveform (red) in a magnetic circuit of electromagnetic actuator. ... A voltage-controlled amplifier is an electronic amplifier that varies its gain depending on a control voltage (often abbreviated CV). ... An ADSR envelope is a parameter used in synthesizers, including those that produce sound by subtractive synthesis, to control the sound produced. ... A low-pass filter is a filter that passes low frequencies but attenuates (or reduces) frequencies higher than the cutoff frequency. ... Wah-wah is an imitative word for the sound of bending or altering musical notes to improve expressiveness, sounding much like a human voice saying the syllable wah for each note. ... LFO section of a modern synthesizer The term low-frequency oscillation (LFO) is an audio signal usually below 20 Hz which creates a pulsating rhythm rather than a audible tone. ...

• Arpeggios, with filter modulation (help·info)

External links

• Buzz Tracker - A freeware electronic music program which could be used to explore this topic further. The example here was generated in Buzz.
• AMS - A free software synthesis program for ALSA.