Synthesizer Keyboards

A synthesizer (spelling var. synthesiser in British English ) is an electronic musical instrument designed to produce electronically generated sound, using techniques such as additive, subtractive, FM, physical modelling synthesis, or phase distortion.

Synthesizers create sounds through direct manipulation of electrical voltages (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 voltages generated by the synthesizer 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).

Synthesizers typically have a keyboard which provides the human interface to the instrument and are often thought of as keyboard instruments. However, a synthesizer's human interface does not necessarily have to be a keyboard, nor does a synthesizer strictly need to be playable by a human. Different fingerboard synthesizer or ribbon controlled synthesizers have also been developed. (See sound module.)

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

1 Sound basics

2 Overview of popular synthesis methods

3 Synthesizer basics

4 The start of the analog synthesizer era

4.1 Homemade synthesizers

5 Electronic organs vs. synthesizers  

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 primarily located close to the integer multiples of the tone's fundamental frequency.

Percussives and rasps usually lack harmonics, and exhibit spectra that are comprised mainly 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.

Schematic of ADSROne of the most salient aspects of any sound is its 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 Decay Sustain Release) envelope model applied to control oscillator volumes. Apart from Sustain, each of these stages is modeled by a change in volume (typically exponential).

Attack time is the time taken for initial run-up of the sound level from nil to 100%.

Decay time is the time taken for the subsequent run down from 100% to the designated Sustain level.

Sustain level, the third stage, is the steady volume produced when a key is held down.

Release time is the time taken for the sound to decay from the Sustain level to nil when the key is released. If a key is released during the Attack or Decay stage, the Sustain phase is usually skipped. Similarly, a Sustain level of zero will produce a more-or-less piano-like (or percussive) envelope, with no continuous steady level, even when a key is held. 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 can be modeled well without this refinement. This refinement is necessary to generate a vibrato.

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 modeling 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 lowpass or bandpass filters following the oscillator stage.

One of the easiest synthesis systems is to record a real instrument as a digitized waveform, 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.. See also: Sample-based synthesis.

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. These techniques tend to be mathematically related, especially frequency modulation and phase modulation.

Subtractive synthesis

Additive synthesis

Granular synthesis

Wavetable synthesis

Frequency modulation synthesis

Phase distortion synthesis

Physical modelling synthesis

Sampling

Subharmonic synthesis

The start of the analog synthesizer era

The first electric musical synthesizer was invented in 1876 by Elisha Gray [1], who was also an independent inventor of the telephone. The "Musical Telegraph" was a chance by-product of his telephone technology.

Gray accidentally discovered that he could control sound from a self vibrating electromagnetic circuit and in doing so invented a basic single note oscillator. The Musical Telegraph used steel reeds whose oscillations were created and transmitted, over a telephone line, by electromagnets. Gray also built a simple loudspeaker device in later models consisting of a vibrating diaphragm in a magnetic field to make the oscillator audible.

Other early synthesizers used technology derived from electronic analog computers, laboratory test equipment, and early electronic musical instruments. Another one of the early synthesizers was the ANS synthesizer, a machine that was constructed by the Russian scientist Evgeny Murzin from 1937 to 1957. Only one copy of ANS was built, and it is currently kept at the Lomonosov University in Moscow. In the 1950s, RCA produced experimental devices to synthesize both voice and music. The giant Mark II Music Synthesizer, housed at the Columbia-Princeton Electronic Music Center in New York City in 1958, was only capable of producing music once it had been completely programmed. The vacuum tube system had to be manually patched to create each new type of sound. It used a paper tape sequencer punched with holes that controlled pitch sources and filters, similar to a mechanical player piano but able to generate a wide variety of sounds.

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. Hugh Le Caine, John Hanert, Raymond Scott, Percy Grainger (with Burnett Cross), and others built a variety of automated electronic-music controllers during the late 1940s and 1950s.

By the 1960s, synthesizers were developed that could be played in real time but were confined to studios because of their size. These synthesizers were usually configured using a modular design, with standalone signal sources and processors being connected with patch cords or by other means, and all controlled by a common controlling device.

Early synthesizers were often experimental special-built devices, usually based on the concept of modularity. Donald Buchla, Hugh Le Caine, Raymond Scott and Paul Ketoff were among the first to build such instruments, in the late 1950s and early 1960s. Only Buchla later produced a commercial version.

The first playable modern configurable music synthesizer was created by Robert Moog, who had been a student of Peter Mauzey, one of the engineers of the RCA Mark II. Moog designed the circuits used in his synthesizer while he was at Columbia-Princeton. The Moog synthesizer was first displayed at the Audio Engineering Society convention in 1964. Like the RCA Mark II, it required hours to set up the machine for a new sound, but it was smaller and more flexible. The Moog synthesizer was at first a curiosity, but by 1968 it had caused a sensation.

Micky Dolenz of The Monkees bought one of the first three Moog synthesizers and the first commercial release to feature a Moog synthesizer was The Monkees' fourth album, Pisces, Aquarius, Capricorn, & Jones, Ltd., in 1967, which also became the first album featuring a synthesizer to hit #1 on the charts. Also among the first music performed on this synthesizer was the million-selling 1968 album Switched-On Bach by Wendy Carlos. Switched-On Bach was one of the most popular classical-music recordings ever made. During the late 1960s, hundreds of other popular recordings used Moog synthesizer sounds. The Moog synthesizer even spawned a subculture of record producers who made novelty "Moog" recordings, depending on the odd new sounds made by their synthesizers (which were not always Moog units) to draw attention and sales.

The cover of Switched-On BachMoog also established standards for control interfacing, with a logarithmic 1-volt-per-octave pitch control and a separate pulse triggering signal. This standardization allowed synthesizers from different manufacturers to operate together. Pitch control is usually performed either with an organ-style keyboard or a music sequencer, which produces a series of control voltages over a fixed time period and allows some automation of music production.

Other early commercial synthesizer manufacturers included ARP, who also started with modular synthesizers before producing all-in-one instruments, and British firm EMS.

In 1970, Moog designed an innovative synthesizer with a built-in keyboard and without modular design--the analog circuits were retained, but made interconnectable with switches in a simplified arrangement called "normalization". Though less flexible than a modular design, it made the instrument more portable and easier to use. This first prepatched synthesizer, the Minimoog, became very popular, with over 12,000 units sold. The Minimoog also influenced the design of nearly all subsequent synthesizers.

In the 1970s miniaturized solid-state components allowed synthesizers to become self-contained, portable instruments. They began to be used in live performances. Soon, electronic synthesizers had become a standard part of the popular-music repertoire, with Chicory Tip's "Son of my Father" as the first #1 hit to feature a synthesizer.

The first movie to make use of synthesized music was the James Bond film "On Her Majesty's Secret Service", in 1969. From that point on, a large number of movies were made with synthesized music. A few movies, like 1982's John Carpenter's "The Thing", used all synthesized music in their musical scores.

During the late 1970s and early 1980s, it was relatively easy for one to build their own synthesizer. Designs were published in hobby electronics magazines and complete kits were supplied by companies such as Maplin Electronics in the UK (although often these designs were actually rebranded versions of synths originally built by hobbyists, for example, the Maplin 5600 was a creation of the Australian scientist Trevor Marshall).

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 tonewheel. In more modern electronic organs, electronic oscillators serve to produce the sine waves. Organs tend to use fairly simple "formant" filters to effect changes to the oscillator tone--automation and modulation tend to be limited to simple vibrato.

Most analog synthesizers produce their sound using subtractive synthesis. In this method, a waveform rich in overtones, usually a sawtooth or pulse wave, is produced by an oscillator. The signal is then passed through filters, which preferentially remove some overtones to obtain a sound which may be an imitation of an acoustical instrument, or may be a unique tonality not existing in acoustical form. An ADSR envelope generator then controls a VCA (voltage controlled amplifier) to give the sound a loudness contour.

Other circuits, such as waveshapers and ring modulators, can change the tonality in non-harmonic ways or create distortion effects which are often not found in natural sound sources. In spite of the popularity of modern digital and software-based synthesizers, the purely analog modular synthesizer still has its proponents, with a number of manufacturers producing modules little different from Moog's 1964 circuit designs, as well as many newer variations like the Moogalicious 900, invented in 1998. Article from www.wikipedia.org.

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