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Synthesizer

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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.


The synthesizer is a type of 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 by direct manipulation of electrical currents which are then 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 See also:
2 External links:

Sound basics

When natural tonal instruments' sounds are analyzed as frequency versus time, tonal instruments have a series of harmonics. These harmonics' frequencies are often at multiples of the fundamental tone[?]'s frequency.

Drums and rasps usually lack harmonics. Instead their sound contains all frequencies in a wide band. How bands of frequency decay determines how the drum or rasp sounds.

In some instruments, such as the human voice, wide-spectrum buzzing and hissing noises are also produced.

Each of these distinct components is called a "formant". The distinctive timbre, intonation and attack of a real instrument can be created by mixing together formants whose volumes and frequency vary in ways that resemble the natural instruments' formants. Higher fidelity can be obtained by adding more formants. Usually, four formants persuasively resemble an instrument, while twelve to fifteen are indistinguishable from a recording.

Most often, an "ADSR" envelope model is used to control formants' volumes. "ADSR" is an acronym standing for "Attack, Delay, Sustain, Release." Each of these stages is modelled by a logarithmic change in volume. The attack is the initial run-up of the formant. 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. Logarithmic rates are used because they closely model real physical vibrations, which usually rise or decay logarithmically.

Although real instruments' formants 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.

Formants can be persuasively generated with just sine-wave generators and wide-band random noise generators. This is the technique used in much digital and software synthesis. The sine waves are generated by look-up tables, and the noise by pseudo-random number generators.

Subtractive synthesizers (see below) were (in their time) economical alternatives that attempted to provide several harmonics or formants at a time by filtering one or a few electronic signal generator(s). This technique provides a "classic synthesizer" sound. Some software and digital synthesizers also provide this system.

One of the easiest synthesis systems is to record a real instrument, and then play back its recordings at different speeds to get 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 Mini-moog[?] 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, 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:



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