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The term "synthesiser" is also used to mean frequency synthesiser, an electronic system found in communications. This article is about the musical instrument.

A synthesizer is an electronic musical instrument designed to produce artificially generated sound, using techniques such as additive, subtractive, FM and physical modelling synthesis to create sounds.

Synthesizers create sounds through direct manipulation of electrical currents (as in analog synthesizers), mathematical manipulation of discrete values using computers (as in software synthesizers), or by a combination of both methods. In the final stage of the synthesizer, electrical currents are used to cause vibrations in the diaphragms of loudspeakers, headphones, etc. This synthesized sound is contrasted with recording of natural sound, where the mechanical energy of a sound wave is transformed into a signal which will then be converted back to mechanical energy on playback (though sampling significantly blurs this distinction).

The term "speech synthesizer" is also used in electronic speech processing, often in connection with vocoders.

Table of contents
1 Sound basics
2 Overview of popular synthesis methods
3 Synthesizer basics
4 The start of the analog synthesizer era
5 Electronic organs vs. synthesizers
6 Early polyphonic synthesizers
7 Microprocessor controlled analog synthesizers
8 MIDI control
9 Early academic digital synthesis research
10 Early commercial digital synthesizers: the FM synthesis era
11 Samplers and sampling
12 The modern digital synthesizer
13 Software-only synthesis
14 Commercial synthesizer manufacturers
15 Classic synthesizer designs
16 See also:
17 External links:

Sound basics

When natural tonal instruments' sounds are analyzed in the frequency domain, the spectra of tonal instruments exhibit amplitude peaks at the harmonics. These harmonics' frequencies are located close to the integer multiples of the tone's fundamental frequency.

Percussivess and rasps usually lack harmonics and exhibit spectra that are comprised instead of noise shaped by the resonant frequencies of the structures that produce the sounds. The resonant properties of the instruments (the spectral peaks of which are also referred to as formants) also shape the spectra of string, wind, voice and other natural instruments.

In most conventional synthesizers, for purposes of resynthesis, recordings of real instruments can be thought to be composed of several components.

These component sounds represent the acoustic responses of different parts of the instrument, the sounds produced by the instrument during different parts of a performance, or the behaviour of the instrument under different playing conditions (pitch, intensity of playing, fingering, etc...) The distinctive timbre, intonation and attack of a real instrument can therefore be created by mixing together these components in such a way as resembles the natural behaviour of the real instrument. Nomenclature varies by synthesizer methodology and manufacturer, but the components are often referred to as oscillators or partials. A higher fidelity reproduction of a natural instrument can typically be achieved using more oscillators, but increased computational power and human programming is required, and most synthesizers use between one and four oscillators by default.

One of the most salient aspects of any sound is it's amplitude envelope. This envelope determines whether the sound is percussive, like a snare drum, or persistent, like a violin string. Most often, this shaping of the sound's amplitude profile is realized with an "ADSR" (Attack Delay Sustain Release) envelope model applied to control oscillator volumes. Each of these stages is modelled by a change in volume (typically exponential). The attack is the initial run-up of the oscillator. The delay is the run down after the attack. Sustain is the volume when the note is held. The release is the volume profile when the note is released. Exponential rates are commonly used because they closely model real physical vibrations, which usually rise or decay exponentially.

Although the oscillations in real instruments also change frequency, most instruments other than the viol-family and human voice can be modelled well without this refinement. This refinement is necessary to generate a vibrato.

Overview of popular synthesis methods

Subtractive synthesizers use a simple acoustic model that assumes an instrument can be approximated by a simple signal generator (producing sawtooth waves, square waves, etc...) followed by a filter which represents the frequency-dependent losses and resonances in the instrument body . For reasons of simplicity and economy, these filters are typically low-order lowpass filters. The combination of simple modulation routings (such as pulse width modulation and oscillator sync), along with the physically unrealistic lowpass filters, is responsible for the "classic synthesizer" sound commonly associated with "analog synthesis" and often mistakenly used when referring to software synthesizers using subtractive synthesis. Although physical modelling synthesis, synthesis wherein the sound is generated according to the physics of the instrument, has superseded subtractive synthesis for accurately reproducing natural instrument timbres, the subtractive synthesis paradigm is still ubiquitous in synthesizers with most modern designs still offering low-order allpass filters following the oscillator stage.

One of the easiest synthesis systems is to record a real instrument, and then play back its recordings at different speeds to produce different tones. This is the technique used in "sampling." Most samplers designate a part of the sample for each component of the ADSR envelope, and then repeat that section while changing the volume for that segment of the envelope. This lets the sampler have a persuasively different envelope using the same note.

Synthesizer basics

There are two major kinds of synthesizers, analog and digital.

There are also many different kinds of synthesis methods, each applicable to both analog and digital synthesizers.

The start of the analog synthesizer era

Early synthesizers used technology derived from electronic analog computers and laboratory test equipment.

In the 1950s, RCA produced experimental devices to synthesize both voice and music. The Mark II Music Synthesizer (1958) was only capable of producing music once it had been completely programmed; that is, the system had to be completely re-set for each new piece.

In 1958 Daphne Oram at the BBC Radiophonic Workshop produced a novel synthesizer using her "Oramics" technique, driven by drawings on a 35mm film strip. This was used for a number of years at the BBC.

In the mid-1960s, synthesizers were developed which could be played in real time but were confined to studios because of their size. A variety of signal processors were connected to a common controller.

The first widely used electronic instrument was the Moog synthesizer designed by Robert Moog, who set up a company to manufacture them. The first instruments were modular synthesizers, and Moog broke into the mass market with the Minimoog an all-in-one instrument.

The first playable modern configurable music synthesizer was created by Robert Moog in 1964. It took hours to set up the machine for a new sound. Among the first music performed on this synthesizer are the record "The well-tempered synthesizer" and "Switched-on Bach" by Walter Carlos (Wendy Carlos since a sex change operation).

Moog also established standards for control interfacing, with a logarithmic 1-volt-per-octave pitch control and a separate pulse triggering signal.

Other commercial synthesizer manufacturers included ARP Instruments, Inc, who also started with modular synthesizers before producing all-in-one instruments.

In the 1970s miniaturized solid-state components let synthesizers become self-contained and movable. They began to be used in live performances.

Electronic organs vs. synthesizers

All organs (including acoustic) are based on the principle of additive or fourier synthesis: Several sine tones are mixed to form a more complex waveform. In the original Hammond organ, built in 1935, these sine waves were generated using revolving tone wheels which induced a current in an electromagnetic pick-up. For every harmonic, there had to be a separate tone wheel.

In more modern electronic organs, oscillators serve to produce the sine waves.

Most analog synthesizers produce their sound using subtractive synthesis, which means filters and amplifiers are used to manipulate a square or saw-tooth wave produced by an oscillator.

Early polyphonic synthesizers

(Polymoog, Oberheim 4-voice)

Microprocessor controlled analog synthesizers

(Sequential Circuits Prophet synth?)

MIDI control

Synthesizers became more usable with the invention in 1983 of MIDI, a digital control interface, and later with the creation of all-digital synthesizers and samplers.

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Early academic digital synthesis research

(Stanford, IRCAM etc)

Early commercial digital synthesizers: the FM synthesis era

(Yamaha DX synthesizer... 1980s FM sound)

Samplers and sampling

One kind of synthesizer, which starts with a recording of an existing sound, which is then replayed at a range of pitches, is called a sampler (see). Sampling can also be used in combination with other synthesizer effects.

The modern digital synthesizer

Most modern synthesizers are now completely digital, including those which model analog synthesis using digital techniques. Digital synthesizers use digital signal processing (DSP) techniques to make musical sounds. Some digital synthesizers now exist in the form of 'softsynth' software that synthesizes sound using conventional PC hardware. Others typically use specialized DSP hardware.

Digital synthesis generates a particular sound pressure on each of (usually) 44.l thousand samples per second. The basic system is that each digital oscillator is modelled by a counter. Each sample, the counter of each oscillator is advanced by an amount that varies depending on the frequency of the oscillator.

For harmonic oscillators, the most significant bits of the counter are used to index a table of a quarter-wive of a cosine function.

For random-noise oscillators, the most significant bits index a table of random numbers.

The numbers from all the oscillators are mixed, and then sent to a digital-to-analog converter, followed by an analog amplifier.

To eliminate the difficult multiplication step in the envelope generation and mixing, some synthesizers perform all of the above operations in a logarithmic coding, and add the current ADSR and mix levels to the logarithmic value of the oscillator, to effectively multiply it. To add the values in the last step of mixing, they are converted to linear values.

Software-only synthesis

The earliest digital synthesis was performed by software synthesizers on mainframe computers using methods exactly like those described in digital synthesis. Music was coded using punch cards to describe the type of instrument, note and duration. The formants of each timbre were generated as a series of sine waves, converted to fixed-point binary suitable for digital-to-analog converters, and mixed by adding and averaging. The data was written slowly to computer tape and then played back in real time to generate the music.

Commercial synthesizer manufacturers

Notable synthesizer manufacturers past and present include:

Classic synthesizer designs

This is intended to be a list of classic instruments which marked a turning point in musical sound or style, potentially worth an article of their own. They are listed with the names of performers or styles associated with them.

See also:

External links: