Synthesizer

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Oberheim OB 12 synthesizer.

A synthesizer (or synthesiser, properly "sound" or "music" synthesizer, often abbreviated to "synth") is an electronic instrument that utilizes multiple sound generators to create complex waveforms that can be combined into countless sonic variations through various waveform synthesis techniques.

"Synths" generate sounds and percussion sets by utilizing a number of different technologies or programmed algorithms, each with their own strengths and weaknesses. Among the most popular waveform synthesis techniques are subtractive synthesis, additive synthesis, granular synthesis, wavetable synthesis, frequency modulation synthesis, phase distortion synthesis, physical modeling synthesis, sample-based synthesis and subharmonic 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 violins, guitars and wind-instruments: there are also several automatic means of electronic control.

[edit] History

For further information see: Electronic music instruments

The first electric synthesizer was invented in 1876 by Elisha Gray, who is best known for his development of a telephone prototype.^[1][2] The Hammond Novachord was an early but unsuccessful harbinger of synth technology in the 1930s-40s. Robert Moog introduced the first commercially-available modern synthesizer in the 1960s. In the 1970s the development of miniaturized solid-state components allowed synthesizers to become self-contained, portable instruments. By the early 1980s companies were selling compact, modestly-priced synthesizers and the development of Musical Instrument Digital Interface (MIDI) made it easier to integrate and synchronize synthesizers and other electronic instruments. In the 1990s synthesizers began to appear as computer software.

	Wendy Carlos - Switched-On Bach First Movement (Allegro) of Brandenburg Concerto Number 3 .
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The synthesizer had a considerable impact on 20th century music.^[3] 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.^[4] It reached #1 on the charts. Walter (later Wendy) Carlos's Switched-On Bach (1968), recorded using Moog synthesizers, influenced numerous musicians of that era and is one of the most popular recordings of classical music ever made.^[5] The sound of the Moog also reached the mass market with The Beatles' Abbey Road and Simon and Garfunkel's Bridge over Troubled Water in 1969, and 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 sizeable 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, Pete Townshend and Arthur Brown.

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

During the 1970s Jean Michel Jarre 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, via David Bowie during his Berlin period (1976-77), were crucial in the development of the genre.^[6] Nick Rhodes, keyboardist of Duran Duran, used Roland Jupiter-4 and Jupiter-8 synthesizers.^[7] 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".^[8] Other chart hits include Depeche Mode's "Just Can't Get Enough" (1981),^[8] and The Human League's "Don't You Want Me".^[9] English musician Gary Numan's 1979 hit "Are 'Friends' Electric?" and 1980's "Cars" used synthesizers heavily^{[10] [11]} Other notable synthpop groups included Visage, Japan, Ultravox,^[6] Spandau Ballet, Culture Club, Eurythmics and Blancmange, and synthesizers became one of the most important instruments in the music industry.^[6] Other notable users include Giorgio Moroder, Larry Fast, Kitaro, Stevie Wonder, Peter Gabriel, Lights (musician), Kate Bush, Frank Zappa, Yellow Magic Orchestra and Devo.

[edit] Types of synthesis

Additive synthesis builds sounds by adding harmonically related waveforms. An early analog example of an additive synthesizer is the Hammond organ. Additive synthesis is also the principle of Wavetable synthesis, which is used to implement real-time synthesis with minimum hardware,^[12] 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 is a process that usually involves the use of at least two signal generators (commonly referred to as "operators") 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. More sophisticated FM synths can use up to 4 or 6 operators per voice and 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 totally unique.

Phase distortion synthesis is a method implemented on Casio CZ synthesizers.

Granular synthesis is a type of synthesis is based on manipulating very small sample slices.

Physical modeling 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.

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.

[edit] 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 which may include:

• Electronic oscillators - create raw sounds with a timbre that depends upon the waveform generated. Voltage controlled oscillators and digital oscillators may be used. 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.

• ADSR envelopes - provide envelope modulation to "shape" the produced note in the time domain. These are used in most forms of synthesis.

• Filters - "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.

• 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 form of synthesis.

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

[edit] ADSR envelope

Schematic of ADSR

When a mechanical musical instrument produces sound the loudness of the sound changes over time in a way that varies from instrument to instrument. The "attack" and "decay" of a sound has a great effect (along with its spectral content) on the instrument's sonic character.^[13] 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:

• Attack time is the time taken for initial run-up of level from nil to peak.
• Decay time is the time taken for the subsequent run down from the attack level to the designated sustain level.
• Sustain level is the amplitude of the sound during the main sequence of its duration.
• Release time is the time taken for the sound 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. ^[14]The 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.^[15]

inverted ADSR envelope

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.

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.

[edit] 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 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] LFO

Low-frequency oscillation (LFO) is an electronic signal, usually below 20 Hz, that creates a rhythmic pulse or sweep, often used to create vibrato, tremolo and other effects. The abbreviation is also often used to refer to low-frequency oscillators themselves.

[edit] Control interfaces

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;

• Fingerboards
• Wind control
• guitar
• drum pad
• music sequencers
• Body movements
• Tangible interfaces^[16]

[edit] Fingerboard controller

A ribbon controller or other violin-like user interface may be used to control synthesizer parameters. 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 Ondes Martenot, Hellertion, Heliophon, Trautonium, Electro-Theremin, Fingerboard-Theremin and The Persephone. 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.

[edit] Wind controllers

Wind controllers are convenient for woodwind or brass players or emulation, being designed along the lines of those instruments. These may be analog or MIDI controllers or may include built-in synthesizers. In addition to a key arrangement the controller has 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. Melodica or recorder style controllers have included the Variophon, Martinetta, Tubophon and Joseph Zawinul's custom Korg Pepe. A Harmonica style interfaces was the Millionizer.

Trumpet style controllers have included products by Steiner, Yamaha, Morrison and Akai. A breath controller may be used as an adjunct to a conventional synthesizer. The Steiner Master's Touch and products which interface to the Yamaha Breath Controller are examples.^[17][18] Several controllers also provide breath-like articulation capabilities.

[edit] Others

The Ondes Martenot control touche d’intensité, Theremin, footpedal and lightbeam controllers are examples. Envelope following systems, the most sophisticated being the vocoder, follow the power or amplitude of an audio signial, rather than using pressure transducers. Various companies make accordion controllers that use pressure transducers on bellows for articulation. More direct articulation using the vocal tract without breath is the Talk box.

[edit] 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.^[19] 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.^[20] MIDI is an opto-isolated serial interface and communication protocol.^[20] 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).^[20]

The General MIDI (GM) software standard was devised in 1991 to serve as a consistent way of describing a set of over 200 tones (including percussion) available to a PC for playback of musical scores.^[21] For the first time, a given MIDI preset would consistently produce an instrumental sound on any GM-conforming 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 exchange of 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 a proposed replacement for MIDI, and is 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.

[edit] Arpeggiator

An arpeggiator is a feature available on some synthesisers 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 to manipulate the order and speed in which the notes play; upwards, downwards, or in a random order. More advanced arpeggiators allow the user to step through a complex sequence of notes or play several arpeggios at once. Some allow a pattern to be sustained even if the keys are released: in this way an arpeggiated pattern may be built up over time by pressing several keys one after the other. Arpeggiators are also commonly found in sequencing software. Some sequencers expand this 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 synchronised with the tempo of the master clock.

	Sound sample of arpeggiator A sample of Eurodance synthesiser riff with use of rapid 1/16 notes arpeggiator
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Arpeggiators grew from hardware sequencers of the late 1960s and 1970s, such as the 16-step ARP Sequencer, and the sequencers of modular synthesisers and were commonly fitted to keyboard instruments through the late 1970s and early 1980s. Notable examples are the Roland Jupiter 8, Oberheim OB-Xa, 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 is heard playing a C minor chord in random mode. They fell out of favour during the 1980s and early 1990s and were absent from the most popular synthesisers of the period but a resurgence of interest in analog synthesisers during the 1990s, and the use of rapid-fire arpeggios in several popular dance hits, brought with it a resurgence.

[edit] Imitative synthesis

Sound synthesis can be used to mimic acoustic sound sources. The characteristics of a sound, known as pitch and timbre, are defined by the amplitude and pitch of each individual sine wave, collectively known as the partials or harmonics. 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] Patch

A patch, in terms of music synthesizers, is a sound setting. Modular synthesizers used cables to patch 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). After this, an overall sound setting for any type of synthesizer has been known as a patch.

Modern synthesizers can 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 can be 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.

[edit] Demo mode

Demonstration mode is a feature programmed into synthesizers to demonstrate the capabilities of the instrument. When the button for the demo mode is pressed, the synthesizer plays back pre-programmed music that showcases the instrument's variety of sounds, the number of voices the model is able to play at once (polyphony)) and effects that may be applied, such as vibrato, reverb or portamento. The song is written into the synthesizer's firmware at the factory and may either be an arrangement of an existing song or a song composed specifically to showcase the synthesizer's strengths.

[edit] 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 acoustic music. Typically, a synth pad plays many whole or half notes, sometimes holding the same note while a lead voice sings or plays an entire musical phrase. Often, the sounds used for synth pads have a vaguely organ, string, or vocal timbre. 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.

[edit] Bass synthesizer

A 1970s-era Moog Taurus synth

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.

An example of a classic analog bass synthesizer sound. Four sawtooth bass filter sweeps with gradually increasing resonance.

In the 1970s miniaturized solid-state components allowed self-contained, portable instruments such as the Moog Taurus, a 13-note pedal keyboard which was 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. Stevie Wonder introduced synth bass to a wider audience in the early 1970s, notably on Superstition (1972) and Boogie On Reggae Woman (1974). In 1977 Parliament's funk single Flashlight used the bass synthesizer. Lou Reed, widely considered a pioneer of electric guitar textures, played bass synthesizer on "Families", from his 1979 album The Bells.

When the programmable music sequencer became widely available in the 1980s (e.g., the synclavier), bass synths were 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 the 2000s, several companies such as Boss and Akai produced bass synthesizer effect pedals for electric bass 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 synthesiser 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.

[edit] See also

• Computer music
• Electronic keyboards
• Guitar/synthesizer
• Keytar
• List of synthesizer manufacturers
• List of classic synthesizers
• Modular synthesizer
• Musical instrument
• Software synthesizer
• Musitron
• Vocaloid
• Low-frequency oscillation
• Noise gate
• Analytic signal
• Envelope detector

[edit] References

[edit] Further reading

• Gorges, Peter (2005). Programming Synthesizers, Wizoobooks, Germany, Bremen, ISBN 978-3-934903-48-7.

• Schmitz, Reinhard (2005). Analog Synthesis, Wizoobooks, Germany, Bremen, ISBN 978-3-934903-01-2.

• Shapiro, Peter (2000). Modulations: A History of Electronic Music: Throbbing Words on Sound, ISBN 1-891024-06-X.

[edit] External links

• Sound Synthesis Theory wikibook
• Vintagesynth — Vintage Synth Explorer
• Progsounds — Online Synthesizer Resource
• Synth Museum — Vintage Synth Resource
• SoundProgramming.Net - Synthesizer Manual Repository
• 120 years of Electronic Music — Machines used from 1870-1990
• Principles of Sound Synthesis at Salford University

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