synthesizer

A sound synthesizer (often abbreviated as "synthesizer" or "synth") is an electronic instrument capable of producing a wide range of sounds. Synthesizers may either imitate other instruments ("imitative synthesis") or generate new timbres. They can be played (controlled) via a variety of different input devices (including keyboards, music sequencers and instrument controllers). Synthesizers generate electric signals (waveforms), and can finally be converted to sound through the loudspeakers or headphones. Early Minimoog by R.A. Moog Inc. (ca. 1970) Synthesizers use a number of different technologies or programmed algorithms to generate signal, each with their own strengths and weaknesses. 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. Also other sound synthesis methods including subharmonic synthesis used on mixture trautonium, granular synthesis resulting Soundscape or Cloud, are rarely used. (See #Types of synthesis) Synthesizers are often controlled with a piano-style keyboard, leading such instruments to be referred to simply as "keyboards". Several other forms of controller have been devised to resemble fingerboards, guitars (guitar synthesizer), violins, wind instruments (wind controller), drums and percussions (electronic drum), etc. (See #Control interfaces) Synthesizers without controllers are often called "sound modules", and they can be controlled using MIDI or CV/Gate methods.

The beginnings of the synthesizer are difficult to trace because of the varying definitions of the term "synthesizer". There is often confusion between sound synthesizers and arbitrary electric/electronic musical instruments.^[1][2]/ However, the former is distinguished from the latter by its ability to imitate sounds.
For example, one of the earliest electric musical instrument was invented in 1876 by American electrical engineer Elisha Gray, who accidentally discovered that he could control sound from a self-vibrating electromagnetic circuit; in doing so, invented a basic single note oscillator. This musical telegraph used steel reeds, whose oscillations were created and transmitted over a telegraphy line by electromagnets. Gray also built a simple loudspeaker device into later models, consisting of a vibrating diaphragm in a magnetic field, to make the oscillator audible.^[3][4]
Frankly, this instrument was a remote electromechanical musical instrument using telegraphy and electric buzzers, without any other sound synthesis function. However, some people tend to call it "the first synthesizer",^{[1][unreliable source?][2][unreliable source?]} without defining the term "synthesizer".
In 1920s, Arseny Avraamov developed various systems of graphic sonic art.^[5]
In the 1930s and 1940s, the basic elements required for modern analog synthesizers — audio oscillators, filters, envelope controllers for expression, and various effects units — had already appeared and were utilized on several electronic instruments, and even earliest polyphonic synthesizers went into commercial production in the United States and Germany. The Hammond Novachord, released in 1939, was a forerunner of later polyphonic synthesizers and electronic organs, but was discontinued because of World War II, and only 1,069 units were built in the three years of its manufacture. Georges Jenny built his first ondioline in France in 1941.
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".^{[neutrality is disputed][6][7]}
In 1958, USSR engineer Yevgeny Murzin made one of the earliest real-time additive synthesizers, called the ANS.^{[citation needed]}
Although RCA had produced a machine called the Electronic Music Synthesizer in 1951–1952, it would be better classified as a "composition machine", because the sounds were not produced in real time.^[8] RCA later developed the RCA Mark II Sound Synthesizer and installed to Columbia-Princeton Electronic Music Center, the first programmable synthesizer, which was inaugurated in 1957.^[9] 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.^[10]

[edit] Modular synthesizer

Main articles: Modular synthesizer, Harald Bode, Robert Moog, and Moog synthesizer

In 1959–1960, Harald Bode developed a modular synthesizer and sound processor,^[11][12] and in 1961, he wrote a paper exploring the concept of self-contained portable modular synthesizer using newly emerging transistor technology;^[13] also he served as AES session chairman on music and electronic for the fall conventions in 1962 and 1964;^[14] after then, his ideas were adopted by Donald Buchla, Robert Moog, and others.

The Moog modular synthesizer of 1960s-1970s.

Robert Moog released the first commercially available modern synthesizer in 1965.^{[citation needed]} 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, synthesizers began to appear as computer software, known as software synthesizers. Later, VST and other plugins were able to emulate classic hardware synthesizers.

	Wendy Carlos - Switched-On Bach (1968) First Movement (Allegro) of Brandenburg Concerto Number 3 played on synthesizer.
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The synthesizer had a considerable effect on 20th century music.^[15] 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.^[16] It reached #1 in the charts. A few months later, both the Rolling Stones' "2000 Light Years from Home" and the title track of the Doors' 1967 album Strange Days would also feature a Moog, played by Brian Jones and Paul Beaver respectively. 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,^[17] alongside the records of Isao Tomita (particularly Snowflakes are Dancing in 1974), who in the early 1970s utilized synthesizers to create new artificial sounds (rather than simply mimicking real instruments)^[18] and made significant advances in analog synthesizer programming.^[19]
The sound of the Moog also 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. 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. Other early users included Emerson, Lake & Palmer's Keith Emerson, Pete Townshend, and The Crazy World of Arthur Brown's Vincent Crane. The Perrey and Kingsley album The In Sound From Way Out! using the Moog and tape loops plus other was released in 1966. The first UK no 1 single to feature a Moog prominently was Chicory Tip's 1972 hit Son of My Father.^[20]

[edit] Synthpop

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

Main article: Synthpop

During the 1970s, Jean Michel Jarre, Larry Fast, and Vangelis released successful electronic instrumental albums. The emergence of Synthpop, a sub-genre of New Wave, in the late 1970s can be largely credited to synthesizer technology. The ground-breaking work of all-electronic German bands such as Kraftwerk and Tangerine Dream, David Bowie during his Berlin period (1976–1977),^[21] as well as the pioneering work of the Japanese Yellow Magic Orchestra and British Gary Numan,^[22] were crucial in the development of the genre.^[21][22] Nick Rhodes, keyboardist of Duran Duran, used various synthesizers, including Roland Jupiter-4 and Jupiter-8.^{[23][dead link]} OMD's "Enola Gay" (1980) used a distinctive electronic percussion and synthesized melody. Soft Cell used a synthesized melody on their 1981 hit "Tainted Love".^[24] Other chart hits include Depeche Mode's "Just Can't Get Enough" (1981),^[24] and The Human League's "Don't You Want Me".^[25] English musician Gary Numan's 1979 hits "Are 'Friends' Electric?" and "Cars" used synthesizers heavily.^[26][27] Other notable synthpop groups included New Order, Visage, Japan, Ultravox,^[21] Spandau Ballet, Culture Club, Eurythmics, Yazoo, Thompson Twins, A Flock of Seagulls, Erasure, Blancmange, Kajagoogoo, Devo, and the early work of Tears for Fears. The synthesizer then became one of the most important instruments in the music industry.^[21] Other notable users include Giorgio Moroder, Howard Jones, Kitaro, Stevie Wonder, Peter Gabriel, Thomas Dolby, Kate Bush,and Frank Zappa.

[edit] Types of synthesis

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

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

Additive synthesis builds sounds by adding together waveforms (which are usually harmonically related). An early analog example of an additive synthesizer is the Hammond organ. To implement real-time additive synthesis, Wavetable synthesis is useful for reducing required hardware/processing power,^[28] and is commonly used in low-end MIDI instruments (such as educational keyboards) and low-end sound cards.
Subtractive synthesis is based on filtering harmonically rich waveforms. Due to its simplicity, it is the basis of early synthesizers such as the Moog synthesizer. 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. 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.

FM synthesis was huge successful as 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 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 DX-7 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 is quite similar to FM synthesis but avoids infringing on the Chowning FM patent. Also it should be categorized to modulation synthesis along with FM synthesis, and also to distortion synthesis along with waveshaping synthesis, and discrete summation formulas.
Granular synthesis is a type of synthesis based on manipulating very small sample slices.

Physical modelling synthesis is often implemented as software synthesizers.

Physical modelling synthesis is the synthesis of sound by using a set of equations and algorithms to simulate a real instrument, or some other physical source of sound. This involves taking up models of components of musical objects and creating systems which define action, filters, envelopes and other parameters over time. The definition of such instruments is virtually limitless, as one can combine any given models available with any amount of sources of modulation in terms of pitch, frequency and contour. For example, the model of a violin with characteristics of a pedal steel guitar and perhaps the action of piano hammer. 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 wasn't until the development of the Karplus-Strong algorithm and the increase in DSP power in the late 1980s that commercial implementations became feasible. Physical modeling on computers gets better and faster with higher processing.

Analysis/resynthesis is typically known as vocoder.

Sample-based synthesis is one of the most popular family of synthesis on today.

Sample-based synthesis 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 Wavetable synthesis, Vector synthesis, etc.
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 resulting analysis data is then used in a second stage 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.

[edit] Imitative synthesis

Sound synthesis can be used to mimic acoustic sound sources. Generally, a sound that does not change over time will include 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 will exhibit 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 will 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.)

[edit] Components

Basic components of an analogue subtractive synthesizer

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 which 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.

• 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.

• Voltage-controlled amplifier (VCA) – After the signal generated by one (or a mix of more Voltage-controlled oscillators), modified by filters and LFOs, and the signal's waveform is shaped (contoured) by an ADSR Envelope Generator, it then passes on to one or more voltage-controlled amplifiers (VCA) where. The VCA is a preamp that boosts (amplifies) the electronic signal before passing on to an external or built-in power amplifier, as well as a means to control its volume using an attenuator that affects a control voltage (coming from the keyboard or other trigger source), which affects the gain of the VCA.^[29]

• ADSR envelopes - provide envelope modulation to "shape" the volume or harmonic content of the produced note in the time domain with the principle parameters being attack, decay, sustain and release. These are used in most forms of synthesis. ADSR control is provided by Envelope Generators.

• 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.

• Other sound processing effects such as ring modulators may be encountered.

[edit] Filter

Various filter modes.

Main article: Voltage controlled filter

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 will produce a flat sound with no envelope. When turned up the envelope becomes more noticeable, expanding the minimum and maximum range of the filter.

[edit] 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.^[30] 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" (Attack Decay Sustain Release) 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:

Schematic of ADSR

		Attack	Decay	Sustain	Release
Key	on				off

Inverted ADSR envelope

• 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 polyphonic 1938 Hammond Novachord (which predates the first Moog synthesizer by over 25 years). A seven-position rotary knob set ADS for all 72 notes; a footpedal controlled release.^[31] 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, and earlier parameter notations (T₁, T₂, E_sus, T₃) were finally simplified to current form by ARP.^[32]
Some electronic musical instruments allow the ADSR envelope to be inverted, which results in opposite behavior compared to 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.

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 allowed notes to be held 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, which would come before the "attack". Modern synthesizers like the Dave Smith Instruments Prophet '08 have DADSR (delay, attack, decay, sustain, release) envelopes. The delay setting determines how long there is silence after a note is hit, before the attack is heard. Some software synthesizers such as Image-Line's 3xOSC (included for free with their DAW FL Studio) have DAHDSR (delay, attack, hold, decay, sustain, release) envelopes.

LFO section of Access Virus C

[edit] LFO

Main article: Low-frequency oscillation

A low-frequency oscillator (LFO) generates an electronic signal, usually below 20 Hz. LFO signals create a rhythmic pulse or sweep, often used to 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.

[edit] Patch

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 known 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)^[33] 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 which 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 will design a family of synthesizers to be compatible.