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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?

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4 Answers 4

up vote 8 down vote accepted

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.
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+1 for being the most thorough answer. –  Jonathan Van Matre Feb 27 at 18:54
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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.

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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.

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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 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 at 0:29
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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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