Why Polyphonic Instruments?
Remember the step from the mono to poly synthesizer?
The step from the monophonic to polyphonic guitar is not quite the same but of a similar order!
So we think its the next step to take, and technology is available, so its just a matter of time until the music will follow
What do we mean by Polyphonic?
Some say "Hexaphonic", which is only correct as long as the instrument has 6 stings, so we prefer "Polyphonic" here:
Polyphony has its specific meaning in the music history, but the word itself simply means that there are several "sounds" and we understand several "voices" or notes. Of course this is the case for any ordinary guitar, but conventional technology treats all notes as a single sound source - which is often not in the sense of the musician! We are mainly talking about electric instruments here, but even for the acoustics: Ask any luthier whether he would not build a different guitar for each string!
In the seventies, the first instruments picked up each string and processed them separately.
Here some of the possible improvements from Single-String-Processing:
Volume correction of each string
this can help to fix unbalanced pick-ups, or to correct a players habit or simply express a players idea of which strings are important in his playing.
Stereo picture
Polyphonic panning helps to create more involving sounds, giving the impression to listen from within the instrument or for example when accompanying a singer, place the voice in the center and the guitar around it.
Multi-track recording and mixing
It is possible to record each string on a separate channel, so single notes can be edited and polyphonic effects can be applied after the mix. a polyphonic effect can be assembled by inserting a similar effect to each string. to simplify operation, 6 plug-ins can be centrally controlled.
Polyphonic Distortion
For guitars, distortion is the most obvious reason to separate strings, there is no interference between strings. The difference is huge! Here is a closer analysis of the history and meaning of distortion, which helps to understand.
Polyphonic Octivider + Polybass
An Octivider applied to each string sounds a lot more accurate and clean than one, even a good one, applied to a mix of strings. Additionally, its possible to detect the lowest played string and create a bass sound only for that string so the result is a simple bass line - musically more useful than a mix of bass sounds
Polyphonic Envelope
All effects which read or create an envelope work a lot better because for example a monophonic touch-wah filters all strings at once, independent on which string is plucked.
Improved Pitch-Shifting + 12 string
Its amazing how some software like Celemony or the POG can handle pitch shifting of sound mixes, but its always simpler and more accurate to process each string. a special case is the simulation of a 12-string guitar by adding a higher octave of the lower 4 strings.
String Selection
Once separate string signals are available we can detect the loudest, lowest and highest played, the last attacked,,, string and give it a different sound or mute the others or whatever...
Guitar-Synthesizer + Scores
Once pitch can be detected on each string, a synthesizer can be driven. either this happens directly in a Guitar-Synthesizer where the synth can follow the string in various forms or a Guitar-to-MIDI controller can be used to feed any MIDI synthesizer which is pretty limited through the MIDI command set which is based on noteOn and noteOf commands. since the noteON also contains the pitch, and the converter needs some time to detect the pitch, the notes either start late or the pitch is not accurately detected or - in praxis - usually both. the integrated Guitar-Synth has the big advantage to define its internal communication and is able for example to place an attack and adapt the pitch until it becomes precise. Conversion to MIDI can be used to write scores - one of the most popular uses of polyphonic systems!
Modelling
Imitation of other kinds of guitars or pick-ups only works well when strings are treated separately.
Several sounds on one instrument
its possible to apply different effects on each string or convert them to different synth sounds. its as if each string would be a separate instrument!
some of the effects immediately sound better for any kind of playing
others allow to play new sounds with the old guitar technique
others need to be rehearsed, some need heavy musical skills...