Polyphony is a property of musical instruments that means that they can play multiple independent melody lines simultaneously. Instruments featuring polyphony are said to be polyphonic. Instruments that are not capable of polyphony are monophonic or paraphonic.

An intuitively understandable example for a polyphonic instrument is a (classical) piano, on which the player plays different melody lines with the left and the right hand - depending on music style and composition, these may be musically tightly interrelated or may even be totally unrelated to each other, like in parts of Jazz music. An example for monophonic instruments is a trumpet which can generate only one tone (frequency) at a time, except when played by extraordinary musicians.

Synthesizer

Monophonic A monophonic synthesizer or monosynth is a synthesizer that produces only one note at a time, making it smaller and cheaper than a polyphonic synthesizer which can play multiple notes at once. This does not necessarily refer to a synthesizer with a single oscillator; the Minimoog, for example, has three oscillators which are settable in arbitrary intervals, but it can play only one note at a time.

Well-known monosynths include the Minimoog, the Roland TB-303, the Korg Prophecy, and the Korg Monologue.

Duophonic Duophonic synthesizers, such as the ARP Odyssey and Formanta Polivoks built in the 1970s and 1980s respectively, have a capability to independently play two pitches at a time. These synthesizers have at least two oscillators that are separately controllable, and a duophonic keyboard that can generate two control voltage signals for the lowest- and highest-note. When two or more keys are pressed simultaneously, the lowest- and highest-note will be heard. When only one key is pressed, both oscillators are assigned to one note, possibly with a more complex sound.

Paraphonic Paraphonic synthesizers, such as the Solina String Ensemble or Korg Poly-800, were designed to play multiple pitches at the same time by using multiple oscillators, but with a common filter and/or amplifier circuit shared among all the voices. The result is a synthesizer that can play chords, provided all the notes start and end at the same time (homophony). For example, playing a new note on top of notes already held might retrigger the volume envelope for the entire sound. Monophonic synthesizers with more than one oscillator (such as the ARP 2600) can often be patched to behave in a paraphonic manner, allowing for each oscillator to play an independent pitch which is then routed through a common VCF and VCA.

Polyphonic The earliest polyphonic synthesizers were built in the late-1930s, but the concept did not become popular until the mid-1970s. Harald Bode's Warbo Formant Orguel, developed in 1937, was an archetype of a voice allocation polyphonic synthesizer. Novachord by Hammond Organ Company, released in 1939, is a forefather product of frequency divider organs and polyphonic synthesizer. It uses octave divider technology to generate polyphony, and about 1,000 Novachords were manufactured until 1942.

Synths using octave divider Using an octave divider a synthesizer needs only 12 oscillators – one for each note in the musical scale. The additional notes are generated by dividing down the outputs of these oscillators. To produce a note one octave lower, the frequency of the oscillator is divided by two. Polyphony is achieved so long as only one of each note in the scale is played simultaneously.

Hammond Novachord A forefather of octave divider synth and electronic organs.Moog Polymoog Octave divider technology similar to Novachord was used.Korg PE-1000 Polyphonic ensemble keyboard consists with one synth per key (totally 60 synthesizers), based on octave dividerKorg PS-3300 Patchable polyphonic synthesizer consists with three synths per key (totally 144 synthesizers), based on octave divider.

Synths using voice allocation In the early-to-mid-1970s, the voice allocation technology with digital keyboard scanning was independently developed by several engineers and musical instrument manufacturers, including Yamaha, E-mu Systems, , "The first step was to use the new logic chips for monophonic, and then polyphonic keyboards. This was a major advance thanks to the use of digital scanning circuitry ... Tom Oberheim [was ?] licensed the [polyphonic] design as the basis for his Four Voice and Eight Voice polyphonic analogue synths of 1974.", "Emu first applied the new technology to keyboard and sequencer design with the 4060 Polyphonic Keyboard and Sequencer of March 1977" , "Dave Smith, ... He called in at the Emu office in the summer of 1977 to discuss product ideas, and the advice was clear the killer product everyone was looking for at the time was an affordable programmable polyphonic analogue synth. Emu were already working towards such a synth, and had pioneered two of the three design concepts (the microprocessor keyboard, and the analogue chip voice card). All that remained was the microprocessor control of patches. ... Whilst Dave Rossum developed the operating system and oversaw the analog circuit design, Dave Smith focused on making patches programmable and designing the control surface. ... Emu agreed a royalty from Sequential that provided strong revenues once the Prophet 5 took off like a rocket in late 1978 and 1979." and Armand Pascetta (Electro Group).abstract: (quoted from ) , "The musician/technician Armand Pascetta was among the first to tackle synthesizer polyphony. Doing business as Electro Group, Pascetta wired Pratt-Reed keyboards to a unique processor (before microprocessors were commonly available) ... develop keyboards that responded to note velocity, release velocity, and aftertouch, and also allowed advanced functionality including keyboard splits and polyphony portamento. By the mid-1970s he's created pre-MIDI keyboard controllers capable of transmitting more than twelve separate channels of gate and voltage-control data and handling multiple synth modules, even across multiple networked keyboards." The Oberheim Polyphonic Synthesizer, "... 1975. Tom subsequently licensed the polyphonic scanning keyboard developed by E-mu's Dave Rossum and paired it with multiple SEMs. By June 1975 he'd completed his Two Voice and Four Voice synths " and Sequential Circuits Prophet-5 were both developed in collaboration with Dave Rossum of E-mu Systems. , "JL: Your influence in the design of both the Prophet 5 and the equipment of Oberheim Electronics have been grossly overlooked. Would you care to comment on what you've done for both companies? / DR: Let me talk first about Tom Oberheim, whom I met at an AES convention in the spring of 1974. ... Towards the fall of that same year he visited E-mu to see our prototype polyphonic keyboard, and decided that he liked that design too. He felt that it too was patentable, and wanted to use it in a product. So we worked out an arrangement whereby he'd pay us royalties, and could use the circuit, and we would share in them benefits of the patent." , "JL: Your influence in the design of both the Prophet 5 and the equipment of Oberheim Electronics have been grossly overlooked. Would you care to comment on what you've done for both companies? / DR: ... The involvement with the Prophet 5 was very similar. Dave Smith had come to us for design help with other projects, when he decided to get into a synthesizer, he came over and basically started picking our brains from the beginning, which was an intelligent thing to do. We did some specific circuit designs for the Prophet 5, reviewed virtually everything in it, and gave him access to lots of E-mu documentation. Again, we had a royalty arrangement, the product went over well, and we made a lot of money...

Yamaha GX-1 Voice allocation technology was used to assign the limited 8-voices per manual into the notes. It was succeeded by the portable Yamaha CS-80 (1976), which was successful and became one of the most popular polyphonic analog synths.E-mu Modular System In 1974, Dave Rossum and E-mu developed the polyphonic technologies, and in 1977, released the 4060 Polyphonic Keyboard and Sequencer.Oberheim Four Voice (FVS-1) It was developed under the collaboration with E-mu Systems.Live Electronic Orchestra (LEO)by Don Lewis LEO used Armand Pascetta's polyphonic keyboard () to control the multiple synthesizers. Sequential Circuits Prophet-5 One of the most popular polyphonic synth featuring patch memories, also used E-mu's technology.

Number of voices One notable early polyphonic synthesizer, the Prophet 5 released in 1978, had five-voice polyphony. Another notable polyphonic synth, the Yamaha CS-80 released in 1976, had eight-voice polyphony, as did the Yamaha GX-1 with total 18 voice polyphony, released in 1973. Six-voice polyphony was standard by the mid-1980s. With the advent of digital synthesizers, 16-voice polyphony became standard by the late 1980s. 64-voice polyphony was common by the mid-1990s and 128-note polyphony arrived shortly after. There are several reasons for providing such large numbers of simultaneous notes:

Even with only ten fingers, it is possible to play more than ten notes at once. Notes may continue to sound even after a key is released. The synthesizer's resources may still be in use to produce the sound of the previously struck notes tapering off, especially when a sustain pedal is used. A "sound" (also called a "timbre" or "patch") may be generated by more than one oscillator or sound-source to allow more complicated sounds to be produced. A synthesizer with 16 oscillators may be capable of 16-note polyphony only when simple, single-oscillator sounds are produced. If a particular patch requires four oscillators, then the synthesizer is only capable of four-note polyphony. Synthesizers may be configured to produce multiple timbres (multitimbral), particularly necessary when sounds are layered or sequenced. Multitimbral instruments are always polyphonic but polyphonic instruments are not necessarily multitimbral. Some multitimbral instruments have a feature which allows the user to specify the amount of polyphony reserved or allowed for each timbre.

Note priority of synthesizer

Synthesizers generally use oscillators to generate the electric signal that forms the basis of the sound, often with a keyboard to trigger the oscillators. However, multiple oscillators working independently are a considerable challenge to implement. To double the polyphony, not only must the number of oscillators be doubled but the electronics must also function as a switch connecting keys to free oscillators instantaneously, implementing an algorithm that decides which notes are turned off if the maximum number of notes is already sounding when an additional key is pressed. There are several ways to implement this:

Turn off the first note sounded and use the newly freed oscillator to play the new note. With last note priority, priority is based on the order in which keys are played. When new notes are triggered while all voices are playing, the synthesizer frees up polyphony by ending the earliest played sounding note. This is the default mode on most synthesizers. Ignore the newly depressed note. With first note priority, earlier notes are not cut off to make room for later ones, and once maximum polyphony has been reached, the person playing the instrument must stop playing one or more notes in order to trigger new ones. In highest note priority, new notes that are higher in pitch than ones being already played replace currently playing notes from the lowest on up. Lowest note priority works in the same way, but cuts notes from the highest down.

Modern synthesizers and samplers may use additional, multiple, or user-configurable criteria to decide which notes sound.

Other instruments

Keyboard instruments

Acoustic keyboard instruments