Synthesizer

A synthesizer (often abbreviated as synth, also spelled synthesiser) is an electronic musical instrument that generates electric signals that are converted to sound through instrument amplifiers and loudspeakers or headphones. Synthesizers may either imitate instruments like piano, Hammond organ, flute, vocals; natural sounds like ocean waves, etc.; or generate new electronic timbres. They are often played with a musical keyboard, but they can be controlled via a variety of other input devices, including music sequencers, instrument controllers, fingerboards, guitar synthesizers, wind controllers, and electronic drums. Synthesizers without built-in controllers are often called sound modules, and are controlled via USB, MIDI or CV/gate using a controller device, often a MIDI keyboard or other controller.

Synthesizers use various methods to generate electronic signals (sounds). Among the most popular waveform synthesis techniques are subtractive synthesis, additive synthesis, wavetable synthesis, frequency modulation synthesis, phase distortion synthesis, physical modeling synthesis and sample-based synthesis. Other less common synthesis types (see #Sound synthesis) include subharmonic synthesis, a form of additive synthesis via subharmonics (used by mixture trautonium), and granular synthesis, sample-based synthesis based on grains of sound, generally resulting in soundscapes or clouds.

Synthesizers were first used in pop music in the 1960s. In the 1970s, synths were used in disco, especially in the late 1970s. In the 1980s, the invention of the relatively inexpensive, mass market Yamaha DX7 synth made synthesizers widely available. 1980s pop and dance music often made heavy use of synthesizers. In the 2010s, synthesizers are used in many genres of pop, rock and dance music. Contemporary classical music composers from the 20th and 21st century write compositions for synthesizer.

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Early Minimoog by R.A. Moog Inc. (ca. 1970)

History

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Wolfgang von Kempelen's Speaking Machine in 1769–1791 (replica in 2007–2009)
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Rudolph Koenig's sound synthesizer in 1865:
consists of tuning forks, electromagnets, and Helmholtz resonators.

The beginnings of the synthesizer are difficult to trace, as it is difficult to draw a distinction between synthesizers and some early electric or electronic musical instruments.

Early electric instruments

One of the earliest electric musical instruments, the musical telegraph, was invented in 1876 by American electrical engineer Elisha Gray. He accidentally discovered the sound generation from a self-vibrating electromechanical circuit, and invented a basic single-note oscillator. This musical telegraph used steel reeds with oscillations created by electromagnets transmitted over a telegraph line. Gray also built a simple loudspeaker device into later models, consisting of a vibrating diaphragm in a magnetic field, to make the oscillator audible.

This instrument was a remote electromechanical musical instrument that used telegraphy and electric buzzers that generated fixed timbre sound. Though it lacked an arbitrary sound-synthesis function, some have erroneously called it the first synthesizer.

Early additive synthesizer: tonewheel organs

In 1897, Thaddeus Cahill invented the Telharmonium (or Dynamophone), which used dynamos (early electric generator), and was capable of additive synthesis like the Hammond organ, which was invented in 1934. Cahill built 3 versions of the instrument, the first of which, weighed over two tons . Cahill's business was unsuccessful for various reasons (size of system, rapid evolutions of electronics, crosstalk issues on the telephone line etc.), and similar but more compact instruments were subsequently developed, such as electronic and tonewheel organs.

Emergence of electronics and early electronic instruments

In 1906, American engineer, Lee De Forest ushered in the "electronics age". He invented the first amplifying vacuum tube, called the Audion tube. This led to new entertainment technologies, including radio and sound films. These new technologies also influenced the music industry, and resulted in various early electronic musical instruments that used vacuum tubes, including:

Most of these early instruments used "heterodyne circuits" to produce audio frequencies, and were limited in their synthesis capabilities. Ondes Martenot and Trautonium were continuously developed for several decades, finally developing qualities similar to later synthesizers.

Graphical sound

In the 1920s, Arseny Avraamov developed various systems of graphic sonic art, and similar graphical sound systems were developed around the world, such as those as seen on the Holzer 2010. In 1938, USSR engineer Yevgeny Murzin designed a compositional tool called ANS, one of the earliest real-time additive synthesizers using optoelectronics. Although his idea of reconstructing a sound from its visible image was apparently simple, the instrument was not realized until 20 years later, in 1958, as Murzin was "an engineer who worked in areas unrelated to music" (Kreichi 1997).

Subtractive synthesis and polyphonic synthesizer

In the 1930s and 1940s, the basic elements required for the modern analog subtractive synthesizers — audio oscillators, audio filters, envelope controllers, and various effects units — had already appeared and were utilized in several electronic instruments.

The earliest polyphonic synthesizers were developed in Germany and the United States. The Warbo Formant Organ developed by Harald Bode in Germany in 1937, was a four-voice key-assignment keyboard with two formant filters and a dynamic envelope controller and possibly manufactured commercially by a factory in Dachau, according to the 120 years of Electronic Music. The Hammond Novachord released in 1939, was an electronic keyboard that used twelve sets of top-octave oscillators with octave dividers to generate sound, with vibrato, a resonator filter bank and a dynamic envelope controller. During the three years that Hammond manufactured this model, 1,069 units were shipped, but production was discontinued at the start of World War II. Both instruments were the forerunners of the later electronic organs and polyphonic synthesizers.

Monophonic electronic keyboards

In the 1940s and 1950s, before the popularization of electronic organs and the introductions of combo organs, manufacturers developed and marketed various portable monophonic electronic instruments with small keyboards. These small instruments consisted of an electronic oscillator, vibrato effect, passive filters etc. Most of these (except for Clavivox) were designed for conventional ensembles, rather than as experimental instruments for electronic music studios—but they contributed to the evolution of modern synthesizers. These small instruments included:

Other innovations

In the late 1940s, Canadian inventor and composer, Hugh Le Caine invented the Electronic Sackbut, a voltage-controlled electronic musical instrument that provided the earliest real-time control of three aspects of sound (volume, pitch, and timbre)—corresponding to today's touch-sensitive keyboard, pitch and modulation controllers. The controllers were initially implemented as a multidimensional pressure keyboard in 1945, then changed to a group of dedicated controllers operated by left hand in 1948.

In Japan, as early as in 1935, Yamaha released Magna organ, a multi-timbral keyboard instrument based on electrically blown free reeds with pickups. It may have been similar to the electrostatic reed organs developed by Frederick Albert Hoschke in 1934 and then manufactured by Everett and Wurlitzer until 1961.

In 1949, Japanese composer Minao Shibata discussed the concept of "a musical instrument with very high performance" that can "synthesize any kind of sound waves" and is "...operated very easily," predicting that with such an instrument, "...the music scene will be changed drastically."

Electronic music studios as sound synthesizers

After World War II, electronic music including electroacoustic music and musique concrète was created by contemporary composers, and numerous electronic music studios were established around the world, especially in Bonn, Cologne, Paris and Milan. These studios were typically filled with electronic equipment including oscillators, filters, tape recorders, audio consoles etc., and the whole studio functioned as a "sound synthesizer".

Origin of the term "sound synthesizer"

In 1951–1952, RCA produced a machine called the Electronic Music Synthesizer; however, it was more accurately a composition machine, because it did not produce sounds in real time. RCA then developed the first programmable sound synthesizer, RCA Mark II Sound Synthesizer, installing it at the Columbia-Princeton Electronic Music Center in 1957. Prominent composers including Vladimir Ussachevsky, Otto Luening, Milton Babbitt, Halim El-Dabh, Bülent Arel, Charles Wuorinen, and Mario Davidovsky used the RCA Synthesizer extensively in various compositions.

From modular synthesizer to popular music

In 1959–1960, Harald Bode developed a modular synthesizer and sound processor, and in 1961, he wrote a paper exploring the concept of self-contained portable modular synthesizer using newly emerging transistor technology. He also served as AES session chairman on music and electronic for the fall conventions in 1962 and 1964. His ideas were adopted by Donald Buchla and Robert Moog in the United States, and Paolo Ketoff et al. in Italy at about the same time: among them, Moog is known as the first synthesizer designer to popularize the voltage control technique in analog electronic musical instruments.

A working group at Roman Electronic Music Center, composer Gino Marinuzzi, Jr., designer Giuliano Strini, MSEE, and sound engineer and technician Paolo Ketoff in Italy; their vacuum-tube modular "FonoSynth" slightly predated (1957–58) Moog and Buchla's work. Later the group created a solid-state version, the "Synket". Both devices remained prototypes (except a model made for John Eaton who wrote a "Concert Piece for Synket and Orchestra"), owned and used only by Marinuzzi, notably in the original soundtrack of Mario Bava's sci-fi film "Terrore nello spazio" (a.k.a. Planet of the Vampires, 1965), and a RAI-TV mini-series, "Jeckyll".

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The Moog modular synthesizer of 1960s–1970s

Robert Moog built his first prototype between 1963 and 1964, and was then commissioned by the Alwin Nikolais Dance Theater of NY; while Donald Buchla was commissioned by Morton Subotnick. In the late 1960s to 1970s, the development of miniaturized solid-state components allowed synthesizers to become self-contained, portable instruments, as proposed by Harald Bode in 1961. By the early 1980s, companies were selling compact, modestly priced synthesizers to the public. This, along with the development of Musical Instrument Digital Interface (MIDI), made it easier to integrate and synchronize synthesizers and other electronic instruments for use in musical composition. In the 1990s, synthesizer emulations began to appear in computer software, known as software synthesizers. From 1996 onward, Steinberg's Virtual Studio Technology (VST) plug-ins – and a host of other kinds of competing plug-in software, all designed to run on personal computers – began emulating classic hardware synthesizers, becoming increasingly successful at doing so during the following decades.

The synthesizer had a considerable effect on 20th-century music. Micky Dolenz of The Monkees bought one of the first Moog synthesizers. The band was the first to release an album featuring a Moog with Pisces, Aquarius, Capricorn & Jones Ltd. in 1967, which reached number 1 in the charts. A few months later the title track of the Doors' 1967 album Strange Days featured a Moog played by Paul Beaver. In the same year, Bruce Haack built a homemade synthesizer that he demonstrated on Mister Rogers' Neighborhood. The synthesizer included a sampler (musical instrument) that recorded, stored, played, and looped sounds controlled by switches, light sensors, and human skin contact. Wendy Carlos's Switched-On Bach (1968), recorded using Moog synthesizers, also influenced numerous musicians of that era and is one of the most popular recordings of classical music ever made, alongside the records (particularly Snowflakes are Dancing in 1974) of Isao Tomita, who in the early 1970s utilized synthesizers to create new artificial sounds (rather than simply mimicking real instruments) and made significant advances in analog synthesizer programming.

The sound of the Moog reached the mass market with Simon and Garfunkel's Bookends in 1968 and The Beatles' Abbey Road the following year; hundreds of other popular recordings subsequently used synthesizers, most famously the portable Minimoog. Electronic music albums by Beaver and Krause, Tonto's Expanding Head Band, The United States of America, and White Noise reached a sizable cult audience and progressive rock musicians such as Richard Wright of Pink Floyd and Rick Wakeman of Yes were soon using the new portable synthesizers extensively. Stevie Wonder and Herbie Hancock also played a major role in popularising synthesizers in Black American music. Other early users included Emerson, Lake & Palmer's Keith Emerson, Tony Banks of Genesis, Todd Rundgren, Pete Townshend, and The Crazy World of Arthur Brown's Vincent Crane. In Europe, the first no. 1 single to feature a Moog prominently was Chicory Tip's 1972 hit "Son of My Father".

In 1974, Roland Corporation released the EP-30, the first touch-sensitive electronic keyboard.

Polyphonic keyboards and the digital revolution

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The Prophet-5 synthesizer of the late 1970s-early 1980s.

In 1973, Yamaha developed the Yamaha GX-1, an early polyphonic synthesizer. Other polyphonic synthesizers followed, mainly manufactured in Japan and the United States from the mid-1970s to the early-1980s, and included Roland Corporation's RS-101 and RS-202 (1975 and 1976) string synthesizers, the Yamaha CS-80 (1976), Oberheim's Polyphonic and OBX (1975 and 1979), Sequential Circuits' Prophet-5 (1978), and Roland's Jupiter 4 and Jupiter 8 (1978 and 1981). The success of the Prophet 5, a polyphonic and microprocessor-controlled keyboard synthesizer, aided the shift of synthesizers towards their familiar modern shape, away from large modular units and towards smaller keyboard instruments. This form factor helped accelerate the integration of synthesizers into popular music, a shift that had been lent powerful momentum by the Minimoog, and also later the ARP Odyssey. Earlier polyphonic electronic instruments of the 1970s, rooted in string synthesizers before advancing to multi-synthesizers incorporating monosynths and more, gradually fell out of favour in the wake of these newer, note-assigned polyphonic keyboard synthesizers.

In 1973, Yamaha licensed the algorithms for the first digital synthesis algorithm, frequency modulation synthesis (FM synthesis), from John Chowning, who had experimented with it since 1971. Yamaha's engineers began adapting Chowning's algorithm for use in a commercial digital synthesizer, adding improvements such as the "key scaling" method to avoid the introduction of distortion that normally occurred in analog systems during frequency modulation. In the 1970s, Yamaha were granted a number of patents, under the company's former name "Nippon Gakki Seizo Kabushiki Kaisha", evolving Chowning's early work on FM synthesis technology. Yamaha built the first prototype digital synthesizer in 1974. Yamaha eventually commercialized FM synthesis technology with the Yamaha GS-1, the first FM digital synthesizer, released in 1980. The first commercial digital synthesizer released a year earlier, the Casio VL-1, released in 1979.

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The Fairlight CMI of the late 1970s-early 1980s.

By the end of the 1970s, digital synthesizers and digital samplers arrived on the market around the world (and are still sold today), as the result of preceding research and development. Compared with analog synthesizer sounds, the digital sounds produced by these new instruments tended to have a number of different characteristics: clear attack and sound outlines, carrying sounds, rich overtones with inharmonic contents, and complex motion of sound textures, amongst others. While these new instruments were expensive, these characteristics meant musicians were quick to adopt them, especially in the United Kingdom and the United States. This encouraged a trend towards producing music using digital sounds, and laid the foundations for the development of the inexpensive digital instruments popular in the next decade (see below). Relatively successful instruments, with each selling more than several hundred units per series, included the NED Synclavier (1978), Fairlight CMI (1979), E-mu Emulator (1981), and PPG Wave (1981).

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The Yamaha DX7 of 1983.

In 1983, however, Yamaha's revolutionary DX7 digital synthesizer swept through popular music, leading to the adoption and development of digital synthesizers in many varying forms during the 1980s, and the rapid decline of analog synthesizer technology. In 1987, Roland's D50 synthesizer was released, which combined the already existing sample-based synthesis and the onboard digital effects, while Korg's even more popular M1 (1988) now also heralded the era of the workstation synthesizer, based on ROM sample sounds for composing and sequencing whole songs, rather than solely traditional sound synthesis.

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The Clavia Nord Lead series released in 1995.

Throughout the 1990s, the popularity of electronic dance music employing analog sounds, the appearance of digital analog modelling synthesizers to recreate these sounds, and the development of the Eurorack modular synthesiser system, initially introduced with the Doepfer A-100 and since adopted by other manufacturers, all contributed to the resurgence of interest in analog technology. The turn of the century also saw improvements in technology that led to the popularity of digital software synthesizers. In the 2010s, new analog synthesizers, both in keyboard instrument and modular form, are released alongside current digital hardware instruments. In 2016, Korg announced the release of the Korg Minilogue, the first polyphonic analogue synth to be mass-produced in decades.

Impact on popular music

In the 1970s, electronic music composers such as Jean Michel Jarre, Vangelis and Isao Tomita, released successful synthesizer-led instrumental albums. Over time, this helped influence the emergence of synthpop, a subgenre of new wave, from the late 1970s to the early 1980s. The work of German krautrock bands such as Kraftwerk and Tangerine Dream, British acts such as Gary Numan and David Bowie, African-American acts such as George Clinton and Zapp, and Japanese electronic acts such as Yellow Magic Orchestra and Kitaro, were influential in the development of the genre. Gary Numan's 1979 hits "Are 'Friends' Electric?" and "Cars" made heavy use of synthesizers. OMD's "Enola Gay" (1980) used distinctive electronic percussion and a synthesized melody. Soft Cell used a synthesized melody on their 1981 hit "Tainted Love". Nick Rhodes, keyboardist of Duran Duran, used various synthesizers including the Roland Jupiter-4 and Jupiter-8.

Chart hits include Depeche Mode's "Just Can't Get Enough" (1981), The Human League's "Don't You Want Me" and Giorgio Moroder's "Take My Breathe Away" (1985) for Berlin. Other notable synthpop groups included New Order, Visage, Japan, Men Without Hats, Ultravox, Spandau Ballet, Culture Club, Eurythmics, Yazoo, Thompson Twins, A Flock of Seagulls, Heaven 17, Erasure, Soft Cell, Pet Shop Boys, Bronski Beat, Kajagoogoo, ABC, Naked Eyes, Devo, and the early work of Tears for Fears and Talk Talk. Giorgio Moroder, Brian Eno, Phil Collins, Howard Jones, Stevie Wonder, Peter Gabriel, Thomas Dolby, Kate Bush, Enya, Mike Oldfield, Dónal Lunny, Frank Zappa and Todd Rundgren all made use of synthesizers.

The synthesizer became one of the most important instruments in the music industry.

Sound synthesis

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Additive synthesis was utilized as early as on Teleharmonium in 1900s and Hammond organ in 1930s.

Additive synthesis builds sounds by adding together waveforms into a composite sound. Instrument sounds are simulated by matching their natural harmonic overtone structure. Early analog examples of additive synthesizers are the Teleharmonium, Hammond organ, and Synclavier.

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Subtractive synthesis is still utilized on various synths, including virtual analog synth.

Subtractive synthesis is based on filtering harmonically rich waveforms. It is implemented in early synthesizers such as the Moog synthesizer. Subtractive synthesizers approximate instrumental sounds by a signal generator (producing sawtooth waves, square waves, etc.) followed by a filter. The combination of simple modulation routings (such as pulse width modulation and oscillator sync), along with the lowpass filter, is responsible for the "classic synthesizer" sound commonly associated with "analog synthesis."

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FM synthesis was hugely successful in earliest digital synthesizers.

FM synthesis (frequency modulation synthesis) is a process that usually involves the use of at least two signal generators (sine-wave oscillators, commonly referred to as "operators" in FM-only synthesizers) to create and modify a voice. Often, this is done through the analog or digital generation of a signal that modulates the tonal and amplitude characteristics of a base carrier signal. FM synthesis was pioneered by John Chowning, who patented the idea and sold it to Yamaha. Unlike the exponential relationship between voltage-in-to-frequency-out and multiple waveforms in classical 1-volt-per-octave synthesizer oscillators, Chowning-style FM synthesis uses a linear voltage-in-to-frequency-out relationship and sine-wave oscillators. The resulting complex waveform may have many component frequencies, and there is no requirement that they all bear a harmonic relationship. Sophisticated FM synths such as the Yamaha DX7 series can have 6 operators per voice; some synths with FM can also often use filters and variable amplifier types to alter the signal's characteristics into a sonic voice that either roughly imitates acoustic instruments or creates sounds that are unique. FM synthesis is especially valuable for metallic or clangorous noises such as bells, cymbals, or other percussion.

Phase distortion synthesis is a method implemented on Casio CZ synthesizers. It replaces the traditional analog waveform with a choice of several digital waveforms which are more complex than the standard square, sine, and sawtooth waves. This waveform is routed to a digital filter and digital amplifier, each modulated by an eight stage envelope. The sound can then be further modified with ring modulation or noise modulation. source: http://manuals.fdiskc.com/flat/Casio%20CZ-101%20Owners%20Manual.pdf

Physical modelling synthesis is the synthesis of sound by using a set of equations and algorithms to simulate each sonic characteristic of an instrument, starting with the harmonics that make up the tone itself, then adding the sound of the resonator, the instrument body, etc., until the sound realistically approximates the desired instrument. When an initial set of parameters is run through the physical simulation, the simulated sound is generated. Although physical modeling was not a new concept in acoustics and synthesis, it was not until the development of the Karplus-Strong algorithm and the increase in DSP power in the late 1980s that commercial implementations became feasible. The quality and speed of physical modeling on computers improves with higher processing power.

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Analysis/resynthesis is typically used on the vocoder.
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Sample-based synthesis may be one of the most popular methods at the moment.

Sample-based synthesis involves digitally recording a short snippet of sound from a real instrument or other source and then playing it back at different speeds to produce different pitches. A sample can be played as a one shot, used often for percussion or short duration sounds, or it can be looped, which allows the tone to sustain or repeat as long as the note is held. Samplers usually include a filter, envelope generators, and other controls for further manipulation of the sound. Virtual samplers that store the samples on a hard drive make it possible for the sounds of an entire orchestra, including multiple articulations of each instrument, to be accessed from a sample library.. See also Wavetable synthesis, Vector synthesis.

Analysis/resynthesis is a form of synthesis that uses a series of bandpass filters or Fourier transforms to analyze the harmonic content of a sound. The results are then used to resynthesize the sound using a band of oscillators. The vocoder, linear predictive coding, and some forms of speech synthesis are based on analysis/resynthesis.

Essynth is a mathematical model for interactive sound synthesis based on evolutionary computation and uses genetic operators and fitness functions to create sound.

Imitative synthesis

Sound synthesis can be used to mimic acoustic sound sources. Generally, a sound that does not change over time includes a fundamental partial or harmonic, and any number of partials. Synthesis may attempt to mimic the amplitude and pitch of the partials in an acoustic sound source.

When natural sounds are analyzed in the frequency domain (as on a spectrum analyzer), the spectra of their sounds exhibits amplitude spikes at each of the fundamental tone's harmonics corresponding to resonant properties of the instruments (spectral peaks that are also referred to as formants). Some harmonics may have higher amplitudes than others. The specific set of harmonic-vs-amplitude pairs is known as a sound's harmonic content. A synthesized sound requires accurate reproduction of the original sound in both the frequency domain and the time domain. A sound does not necessarily have the same harmonic content throughout the duration of the sound. Typically, high-frequency harmonics die out more quickly than the lower harmonics.

In most conventional synthesizers, for purposes of re-synthesis, recordings of real instruments are composed of several components representing the acoustic responses of different parts of the instrument, the sounds produced by the instrument during different parts of a performance, or the behavior of the instrument under different playing conditions (pitch, intensity of playing, fingering, etc.)

Components

Synthesizers generate sound through various analogue and digital techniques. Early synthesizers were analog hardware based but many modern synthesizers use a combination of DSP software and hardware or else are purely software-based (see softsynth). Digital synthesizers often emulate classic analog designs. Sound is controllable by the operator by means of circuits or virtual stages that may include:

  • Electronic oscillators – create raw sounds with a timbre that depends upon the waveform generated. Voltage-controlled oscillators (VCOs) and digital oscillators may be used. Harmonic additive synthesis models sounds directly from pure sine waves, somewhat in the manner of an organ, while frequency modulation and phase distortion synthesis use one oscillator to modulate another. Subtractive synthesis depends upon filtering a harmonically rich oscillator waveform. Sample-based and granular synthesis use one or more digitally recorded sounds in place of an oscillator.
  • Low frequency oscillator (LFO) – an oscillator of adjustable frequency that can be used to modulate the sound rhythmically, for example to create tremolo or vibrato or to control a filter's operating frequency. LFOs are used in most forms of synthesis.
  • Voltage-controlled filter (VCF) – "shape" the sound generated by the oscillators in the frequency domain, often under the control of an envelope or LFO. These are essential to subtractive synthesis.
  • ADSR envelopes – provide envelope modulation to "shape" the volume or harmonic content of the produced note in the time domain with the principal parameters being attack, decay, sustain and release. These are used in most forms of synthesis. ADSR control is provided by envelope generators.
  • Voltage-controlled amplifier (VCA) – After the signal generated by one (or a mix of more) VCOs has been modified by filters and LFOs, and its waveform has been shaped (contoured) by an ADSR envelope generator, it then passes on to one or more voltage-controlled amplifiers (VCAs). A VCA is a preamp that boosts (amplifies) the electronic signal before passing it on to an external or built-in power amplifier, as well as a means to control its amplitude (volume) using an attenuator. The gain of the VCA is affected by a control voltage (CV), coming from an envelope generator, an LFO, the keyboard or some other source.
  • Other sound processing effects such as ring modulators may be encountered.

Filter

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Various filter modes.

Electronic filters are particularly important in subtractive synthesis, being designed to pass some frequency regions through unattenuated while significantly attenuating ("subtracting") others. The low-pass filter is most frequently used, but band-pass filters, band-reject filters and high-pass filters are also sometimes available.

The filter may be controlled with a second ADSR envelope. An "envelope modulation" ("env mod") parameter on many synthesizers with filter envelopes determines how much the envelope affects the filter. If turned all the way down, the filter produces a flat sound with no envelope. When turned up the envelope becomes more noticeable, expanding the minimum and maximum range of the filter.

Attack Decay Sustain Release (ADSR) envelope

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Schematic of ADSR
Attack Decay Sustain Release
Key on off
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Inverted ADSR envelope

When an acoustic musical instrument produces sound, the loudness and spectral content of the sound change over time in ways that vary from instrument to instrument. The "attack" and "decay" of a sound have a great effect on the instrument's sonic character. Sound synthesis techniques often employ an envelope generator that controls a sound's parameters at any point in its duration. Most often this is an (ADSR) envelope, which may be applied to overall amplitude control, filter frequency, etc. The envelope may be a discrete circuit or module, or implemented in software. The contour of an ADSR envelope is specified using four parameters:

  • Attack time is the time taken for initial run-up of level from nil to peak, beginning when the key is first pressed.
  • Decay time is the time taken for the subsequent run down from the attack level to the designated sustain level.
  • Sustain level is the level during the main sequence of the sound's duration, until the key is released.
  • Release time is the time taken for the level to decay from the sustain level to zero after the key is released.

An early implementation of ADSR can be found on the Hammond Novachord in 1938 (which predates the first Moog synthesizer by over 25 years). A seven-position rotary knob set preset ADS parameter for all 72 notes; a pedal controlled release time. The notion of ADSR was specified by Vladimir Ussachevsky (then head of the Columbia-Princeton Electronic Music Center) in 1965 while suggesting improvements for Bob Moog's pioneering work on synthesizers, although the earlier notations of parameter were (T1, T2, Esus, T3), then these were simplified to current form (Attack time, Decay time, Sustain level, Release time) by ARP.

Some electronic musical instruments can invert the ADSR envelope, reversing the behavior of the normal ADSR envelope. During the attack phase, the modulated sound parameter fades from the maximum amplitude to zero then, during the decay phase, rises to the value specified by the sustain parameter. After the key has been released the sound parameter rises from sustain amplitude back to maximum amplitude.

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8-step envelope on Casio CZ series

A common variation of the ADSR on some synthesizers, such as the Korg MS-20, was ADSHR (attack, decay, sustain, hold, release). By adding a "hold" parameter, the system could hold notes at the sustain level for a fixed length of time before decaying. The General Instruments AY-3-8912 sound chip included a hold time parameter only—the sustain level was not programmable. Another common variation in the same vein is the AHDSR (attack, hold, decay, sustain, release) envelope, in which the "hold" parameter controls how long the envelope stays at full volume before entering the decay phase. Multiple attack, decay and release settings may be found on more sophisticated models.

Certain synthesizers also allow for a delay parameter before the attack. Modern synthesizers like the Dave Smith Instruments Prophet '08 have DADSR (delay, attack, decay, sustain, release) envelopes. The delay setting determines the length of silence between hitting a note and the attack. Some software synthesizers, such as Image-Line's 3xOSC (included with their DAW FL Studio) have DAHDSR (delay, attack, hold, decay, sustain, release) envelopes.

A common feature on many synthesizers is an AD envelope (attack and decay only). This can be used to control e.g. the pitch of one oscillator, which in turn may be synchronized with another oscillator by oscillator sync.

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LFO section of Access Virus C

LFO

A low-frequency oscillator (LFO) generates an electronic signal, usually below 20 Hz. LFO signals create a periodic control signal or sweep, often used in vibrato, tremolo and other effects. In certain genres of electronic music, the LFO signal can control the cutoff frequency of a VCF to make a rhythmic wah-wah sound, or the signature dubstep wobble bass.

Arpeggiator

An arpeggiator (arp) is a feature available on several synthesizers that automatically steps through a sequence of notes based on an input chord, thus creating an arpeggio. The notes can often be transmitted to a MIDI sequencer for recording and further editing. An arpeggiator may have controls for speed, range, and order in which the notes play; upwards, downwards, or in a random order. More advanced arpeggiators allow the user to step through a pre-programmed complex sequence of notes, or play several arpeggios at once. Some allow a pattern sustained after releasing keys: in this way, sequence of arpeggio patterns may be built up over time by pressing several keys one after the other. Arpeggiators are also commonly found in software sequencers. Some arpeggiators/sequencers expand features into a full phrase sequencer, which allows the user to trigger complex, multi-track blocks of sequenced data from a keyboard or input device, typically synchronized with the tempo of the master clock.

Arpeggiators seem to have grown from the accompaniment system used in electronic organs in the mid-1960s to the mid-1970s. Also they were commonly fitted to keyboard instruments through the late 1970s and early 1980s. Notable examples are the RMI Harmonic Synthesizer (1974), Roland Jupiter-8, Oberheim OB-8, Roland SH-101, Sequential Circuits Six-Trak and Korg Polysix. A famous example can be heard on Duran Duran's song "Rio", in which the arpeggiator on a Roland Jupiter-4 plays a C minor chord in random mode. They fell out of favor by the latter part of the 1980s and early 1990s and were absent from the most popular synthesizers of the period but a resurgence of interest in analog synthesizers during the 1990s, and the use of rapid-fire arpeggios in several popular dance hits, brought with it a resurgence.

Patch

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One of the earliest patch memory (bottom left) on Oberheim Four-voice (1975/1976)

A synthesizer patch (some manufacturers chose the term program) is a sound setting. Modular synthesizers used cables ("patch cords") to connect the different sound modules together. Since these machines had no memory to save settings, musicians wrote down the locations of the patch cables and knob positions on a "patch sheet" (which usually showed a diagram of the synthesizer). Ever since, an overall sound setting for any type of synthesizer has been referred to as a patch.

In mid–late 1970s, patch memory (allowing storage and loading of 'patches' or 'programs') began to appear in synths like the Oberheim Four-voice (1975/1976) and Sequential Circuits Prophet-5 (1977/1978). After MIDI was introduced in 1983, more and more synthesizers could import or export patches via MIDI SYSEX commands. When a synthesizer patch is uploaded to a personal computer that has patch editing software installed, the user can alter the parameters of the patch and download it back to the synthesizer. Because there is no standard patch language, it is rare that a patch generated on one synthesizer can be used on a different model. However, sometimes manufacturers design a family of synthesizers to be compatible.

Control interfaces

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Non-contact interface (AirFX)
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Tangible interface (Reactable)
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Pitch & mod. wheels and touchpad
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Drum pad
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Guitar-style interface (SynthAxe)

Modern synthesizers often look like small pianos, though with many additional knob and button controls. These are integrated controllers, where the sound synthesis electronics are integrated into the same package as the controller. However, many early synthesizers were modular and keyboardless, while most modern synthesizers may be controlled via MIDI, allowing other means of playing such as:

Fingerboard controller

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Left: Ondes Martenot (6G in 1960)
Right: Mixture Trautonium (replica of 1952)
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Fingerboard
on Korg monotron
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Ribbon controller
on Moog 3P (1972)

A ribbon controller or other violin-like user interface may be used to control synthesizer parameters. The idea dates to Léon Theremin's 1922 first concept and his 1932 Fingerboard Theremin and Keyboard Theremin,  Maurice Martenot's 1928 Ondes Martenot (sliding a metal ring),  Friedrich Trautwein's 1929 Trautonium (finger pressure), and was also later utilized by Robert Moog. The ribbon controller has no moving parts. Instead, a finger pressed down and moved along it creates an electrical contact at some point along a pair of thin, flexible longitudinal strips whose electric potential varies from one end to the other. Older fingerboards used a long wire pressed to a resistive plate. A ribbon controller is similar to a touchpad, but a ribbon controller only registers linear motion. Although it may be used to operate any parameter that is affected by control voltages, a ribbon controller is most commonly associated with pitch bending.

Fingerboard-controlled instruments include the Trautonium (1929), Hellertion (1929) and Heliophon (1936), Electro-Theremin (Tannerin, late 1950s), Persephone (2004), and the Swarmatron (2004). A ribbon controller is used as an additional controller in the Yamaha CS-80 and CS-60, the Korg Prophecy and Korg Trinity series, the Kurzweil synthesizers, Moog synthesizers, and others.

Rock musician Keith Emerson used it with the Moog modular synthesizer from 1970 onward. In the late 1980s, keyboards in the synth lab at Berklee College of Music were equipped with membrane thin ribbon style controllers that output MIDI. They functioned as MIDI managers, with their programming language printed on their surface, and as expression/performance tools. Designed by Jeff Tripp of Perfect Fretworks Co., they were known as Tripp Strips. Such ribbon controllers can serve as a main MIDI controller instead of a keyboard, as with the Continuum instrument.

Wind controllers

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Wind controller
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Accordion synthesizer

Wind controllers (and wind synthesizers) are convenient for woodwind and brass players, being designed to imitate those instruments. These are usually either analog or MIDI controllers, and sometimes include their own built-in sound modules (synthesizers). In addition to the follow of key arrangements and fingering, the controllers have breath-operated pressure transducers, and may have gate extractors, velocity sensors, and bite sensors. Saxophone-style controllers have included the Lyricon, and products by Yamaha, Akai, and Casio. The mouthpieces range from alto clarinet to alto saxophone sizes. The Eigenharp, a controller similar in style to a bassoon, was released by Eigenlabs in 2009. Melodica and recorder-style controllers have included the Martinetta (1975) and Variophon (1980), and Joseph Zawinul's custom Korg Pepe. A harmonica-style interface was the Millionizer 2000 (c. 1983).

Trumpet-style controllers have included products by Steiner/Crumar/Akai, Yamaha, and Morrison. Breath controllers can also be used to control conventional synthesizers, e.g. the Crumar Steiner Masters Touch, Yamaha Breath Controller and compatible products. Several controllers also provide breath-like articulation capabilities.

Accordion controllers use pressure transducers on bellows for articulation.

Others

Other controllers include theremin, lightbeam controllers, touch buttons (touche d’intensité) on the ondes Martenot, and various types of foot pedals. Envelope following systems, the most sophisticated being the vocoder, are controlled by the power or amplitude of input audio signal. A musician uses the talk box to manipulate sound using the vocal tract, though it is rarely categorized as a synthesizer.

MIDI control

Synthesizers became easier to integrate and synchronize with other electronic instruments and controllers with the introduction of Musical Instrument Digital Interface (MIDI) in 1983. First proposed in 1981 by engineer Dave Smith of Sequential Circuits, the MIDI standard was developed by a consortium now known as the MIDI Manufacturers Association. MIDI is an opto-isolated serial interface and communication protocol. It provides for the transmission from one device or instrument to another of real-time performance data. This data includes note events, commands for the selection of instrument presets (i.e. sounds, or programs or patches, previously stored in the instrument's memory), the control of performance-related parameters such as volume, effects levels and the like, as well as synchronization, transport control and other types of data. MIDI interfaces are now almost ubiquitous on music equipment and are commonly available on personal computers (PCs).

The General MIDI (GM) software standard was devised in 1991 to serve as a consistent way of describing a set of over 200 sounds (including percussion) available to a PC for playback of musical scores. For the first time, a given MIDI preset consistently produced a specific instrumental sound on any GM-compatible device. The Standard MIDI File (SMF) format (extension .mid) combined MIDI events with delta times – a form of time-stamping – and became a popular standard for exchanging music scores between computers. In the case of SMF playback using integrated synthesizers (as in computers and cell phones), the hardware component of the MIDI interface design is often unneeded.

Open Sound Control (OSC) is another music data specification designed for online networking. In contrast with MIDI, OSC allows thousands of synthesizers or computers to share music performance data over the Internet in realtime.

Typical roles

Synth lead

In popular music, a synth lead is generally used for playing the main melody of a song, but it is also often used for creating rhythmic or bass effects. Although most commonly heard in electronic dance music, synth leads have been used extensively in hip-hop music since the 1980s and some types of rock songs since the 1970s. Many post-1980s pop music songs use a synth lead to provide a musical hook to sustain the listener's interest throughout a song.

Synth pad

A synth pad is a sustained chord or tone generated by a synthesizer, often employed for background harmony and atmosphere in much the same fashion that a string section is often used in orchestral music and film scores. Typically, a synth pad is performed using whole notes, which are often tied over bar lines. A synth pad sometimes holds the same note while a lead voice sings or plays an entire musical phrase or section. Often, the sounds used for synth pads have a vaguely organ, string, or vocal timbre. During the late 1970s and 1980s, specialized string synthesizers were made that specialized in cresting string sounds using the limited technology of the time. Much popular music in the 1980s employed synth pads, this being the time of polyphonic synthesizers, as did the then-new styles of smooth jazz and new-age music. One of many well-known songs from the era to incorporate a synth pad is "West End Girls" by the Pet Shop Boys, who were noted users of the technique.

The main feature of a synth pad is very long attack and decay time with extended sustains. In some instances pulse-width modulation (PWM) using a square wave oscillator can be added to create a "vibrating" sound.

Synth bass

The bass synthesizer (or "bass synth") is used to create sounds in the bass range, from simulations of the electric bass or double bass to distorted, buzz-saw-like artificial bass sounds, by generating and combining signals of different frequencies. Bass synth patches may incorporate a range of sounds and tones, including wavetable-style, analog, and FM-style bass sounds, delay effects, distortion effects, envelope filters. A modern digital synthesizer uses a frequency synthesizer microprocessor component to generate signals of different frequencies. While most bass synths are controlled by electronic keyboards or pedalboards, some performers use an electric bass with MIDI pickups to trigger a bass synthesizer.

In the 1970s miniaturized solid-state components allowed self-contained, portable instruments such as the Moog Taurus, a 13-note pedal keyboard played by the feet. The Moog Taurus was used in live performances by a range of pop, rock, and blues-rock bands. An early use of bass synthesizer was in 1972, on a solo album by John Entwistle (the bassist for The Who), entitled Whistle Rymes. Genesis bass player Mike Rutherford used a Dewtron "Mister Bassman" for the recording of their album Nursery Cryme in August 1971. Stevie Wonder introduced synth bass to a pop audience in the early 1970s, notably on "Superstition" (1972) and "Boogie On Reggae Woman" (1974). In 1977 Parliament's funk single "Flash Light" used the bass synthesizer. Lou Reed, widely considered a pioneer of electric guitar textures, played bass synthesizer on the song "Families", from his 1979 album The Bells.

Following the availability of programmable music sequencers such as the Synclavier and Roland MC-8 Microcomposer in the late 1970s, bass synths began incorporating sequencers in the early 1980s. The first bass synthesizer with a sequencer was the Firstman SQ-01. It was originally released in 1980 by Hillwood/Firstman, a Japanese synthesizer company founded in 1972 by Kazuo Morioka (who later worked for Akai in the early 1980s), and was then released by Multivox for North America in 1981.

A particularly influential bass synthesizer was the Roland TB-303. Released in late 1981, it featured a built-in sequencer and later became strongly associated with acid house music. Bass synthesizers began being used to create highly syncopated rhythms and complex, rapid basslines. Bass synth patches incorporate a range of sounds and tones, including wavetable-style, analog, and FM-style bass sounds, delay effects, distortion effects, envelope filters. In popular music, these techniques gained wide popularity with the emergence of acid house music, after Phuture's use of the TB-303 for the single "Acid Tracks" in 1987, though such techniques were predated by Charanjit Singh's use of the TB-303 in 1982.

In the 2000s, several equipment manufacturers such as Boss and Akai produced bass synthesizer effect pedals for electric bass guitar players, which simulate the sound of an analog or digital bass synth. With these devices, a bass guitar is used to generate synth bass sounds. The BOSS SYB-3 was one of the early bass synthesizer pedals. The SYB-3 reproduces sounds of analog synthesizers with Digital Signal Processing saw, square, and pulse synth waves and user-adjustable filter cutoff. The Akai bass synth pedal contains a four-oscillator synthesizer with user selectable parameters (attack, decay, envelope depth, dynamics, cutoff, resonance). Bass synthesizer software allows performers to use MIDI to integrate the bass sounds with other synthesizers or drum machines. Bass synthesizers often provide samples from vintage 1970s and 1980s bass synths. Some bass synths are built into an organ style pedalboard or button board.

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