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My digital piano has 88 keys and the manual says it provides 128 voices of polyphony, and this seems not a particular exception or unusual feature.

I even cannot imagine how it would be possible to press all 88 keys all at once or even in a close succession. Ok several keys also must keep sounding while I hold the sustain pedal, but 128?

Why possibly it was required to implement that many voices for the instrument?

14

Modern digital pianos have a number of features that expand the number of notes that might be simultaneously present in the output:

  • Some polyphonic voices last a long time after the key is released, so if you play a lot of notes quickly using these voices, you may end up having dozens, and even a hundred notes still sounding while you're adding new notes.
  • Some can record and play back music, which allows you to, for instance, record an accompaniment which you can then play while playing another layer of music on top. Do this repeatedly and you will have the instrument playing the parts of an entire orchestra.
  • Some have drum tracks you can play in the background behind your music
  • Some have built in audio metronomes, which use one or more voices for their tick sounds
  • Some have midi input, which would allow one to have the instrument play very complex arrangements using dozens or more of simultaneous voices. Some will have a drum track, and play notes for 10-20 different instruments, and it can take many, many polyphonic notes to play that.
  • Some voices are comprised of a few different voices mixed together, so the instrument may only need the memory for 400 voices, but by mixing a few together can generate another one or two hundred voices without more memory.
11

some voices on your digital piano contains more than 1 tone, for example an organ single note may consist of 3 or 4 voice samples (polyphony) so , when you press 10 claviers it will produce about 40 sound samples... 128 voices of polyphony will let you hear your sound fully and without note cancellation.

  • 1
    I think this is wrong. Digital keyboards don't work like hammond organs: a single note for a midi keyboard on an organ voice only triggers 1 sample which already includes all the harmonics within it: it's just an audio file not triggering 10 physical oscillators. – Some_Guy Nov 5 '17 at 1:31
  • @Some_Guy in Digital keyboards you can mix a lot of samples together to produce a new sound so a single note won't always trigger 1 sample. for instance you can mix a piano sample with strings so pressing C3 will play a C3 for piano and another C3 for strings. – Mohammad Rafigh Nov 21 '18 at 9:37
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    that's a better examples for sure, the organ one's not really right but for piano and strings or other combinations it is, absolutely. – Some_Guy Nov 21 '18 at 13:28
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Besides the possibility to have multiple sounds assigned to a single key, another important point is: use of pedal requires the previously sounding notes to continue as opposed to terminate suddenly just to re-use the channel for the new notes.

  • Even without the pedal, a realistic piano sound has a nontrivial "release" time as the string is muted by the felt, and that should be be allowed for before the next note is played by that voice. – keshlam Feb 27 '14 at 17:37
  • @keshlam: Before the generator is recycled for a different pitch, certainly, but if a note is restruck that should essentially nullify its earlier vibrations, should it not? – supercat Feb 28 '14 at 0:29
1

If you use your digital piano to play back MIDI, it might be playing more than 88 notes across several different channels.

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'Voices' are largely a marketing term. It doesn't necessarily equate to 'polyphony'. Does playing a note use one, two or more 'voices'? We don't know and we aren't told. You're fairly safe in assuming that when anything but the cheapest digital piano is playing a piano sound you won't be troubled by note cut-offs due to an inadequate number of voices. Maybe you could set up an experimental situation where this would happen. Enjoy!

  • Perhaps the down-voter could say why? – Laurence Payne Nov 5 '17 at 14:30
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The advertisement of "128 voice polyphony" essentially just means "100% polyphonic", as within general midi there are only 128 notes that exist.

128 is a very convenient number for computing: it's 2 to the power of 7

That is to say, if you have seven binary characters (which you can represent however you want, os and xs, 1s and 0s, TRUE and FALSE) there are 128 possible combinations: ooooooo oooooox oooooxo oooooxx etc. for 128 times until you get to xxxxxxx

Midi is designed around the number 128 (or 127 for values where "0" is significant like velocity). The reason for this is that it's built around a protocol that transmits "bytes" of data. A byte of data consists of 8 bits (8 binary units). Usually this consists of 1 bit specifying the type of value, and 7 bits consisting of the value itself.

MIDI includes 128 notes for this reason: in the MIDI protocol, the first bit tells the instrument whether it is a "status byte" or a "data byte" (not important for this answer) and, for a "note on" or "note off" message, the remaining 7 bits tell you which note the message refers to. So every time you press a key on a midi controller, in a simplified sense, a 0, then a 7 bit integer (a number between 1 and 128 represented by 7 1s and 0s) is sent through the wire.

Now, it might seem a bit wasteful to use a whole bit of a byte on this data type for every note press, but there are good reasons why this is a convenient way to design the protocol, and 128 notes (more than 10 octaves) is enough for pretty much all applications. The next option up would be 256 notes, this would make the engineering more difficult (no status/data indicator bit) and 256 notes puts us well outside the range of human hearing.

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