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I don't want to end up paying more for a digital piano for a higher polyphonic capability if I don't need it.

I was wondering if the polyphony limit on digital pianos is tied to the sound engines they possess, or to the actual physical key presses like on some old computer keyboards.

Essentially, if I connect a Yamaha P45, which has a polyphonic limit of 64, via midi to a piano VST, would I be able to go above that limit?

3 Answers 3

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A VSTi will have its own polyphony limit, completely separate to that of the generating instrument.

This usually comes into play when you're using a lot of pedal. The notes on/off are still generated, but you run out of voices to play back the oldest sustained notes, so they're 'stolen' from the playback engine. Many modern keyboards are smart enough steal the 'least noticeable' note if they have to steal.
This will not affect any note on/off data, as it's the pedal data keeping the sustain going. The key down/up events have all been accounted for.

tbh, I have never tested trying to press more than 64 keys simultaneously to see if it can hold them all in memory waiting for a key-off. It feels like it would be a futile pursuit ;)

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  • Thank your for your quick answer! That's very good to hear I'm pretty sure that answered my question! Just to be 100% sure though, that means that they key presses themselves don't have a limit right?
    – Mavil
    May 26 at 11:13
  • There might be a simultaneous keypress limit, as intimated, but holding down more than 64 keys at once is really not all that common. I used to work for Yamaha R&D, & honestly, this was never even mentioned.
    – Tetsujin
    May 26 at 11:16
  • True true... Thank you again so much!! You really cleared this up a lot for me! Have a fantastic day :D
    – Mavil
    May 26 at 11:17
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Computer keyboards are typically wired as a scanned matrix. The keyboard hardware drives each row, and then sees which columns are connected. If three keys that are pressed simultaneously would form three corners of a rectangle in the matrix, then both rows and both columns will be connected to each other, and the hardware will have no way of determining which three corners of the rectangle are pressed, or whether all four are pressed.

While some cheap toy musical keyboards that are limited to two-note polyphony use such a design, any non-toy keyboard will either include a diode with each key to ensure that all combinations of keys can be read by the matrix, or else use dedicated input circuitry for each key avoiding the "rectangles" problem altogether.

While some keyboards might possibly limit polyphony when outputting MIDI data, supporting 127-note polyphony would not be significantly harder than supporting anything less.

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    For additional info, the term for this is called rollover.
    – Andrew T.
    May 27 at 4:12
  • @AndrewT.: The term "rollover" is sometimes used with a bit more limited meaning than suggested by that article, to describe situations where a transition from having one combination of keys pressed to having some other combination of keys pressed can be reliably handled even if some of the latter keys are pressed before the former keys are released, without reporting any states that have not actually occurred. If a two-key polyphonic keyboard handles rollover correctly and one presses two keys, holds them while pressing two more, and then releases the first two, then...
    – supercat
    May 27 at 21:24
  • ...it will register the latter keys as having been pressed sometime between the time they were and the time the first two keys were released. Overlap may slightly skew the timing with which the latter keys are detected, but won't cause erroneous events. On a keyboard that doesn't handle this correctly, key overlap, no matter how brief, may trigger notes that are just plain wrong.
    – supercat
    May 27 at 21:26
  • Also note that any serious musical keyboard won't just have an on/off switch for its keys, but rather a sophisticated measurement device that allows it to measure how fast and how far each key was pressed. There's definitely no scanned matrix for that.
    – Vilx-
    May 28 at 13:49
  • @Vilx-: Some velocity-sensitive keyboards have two contacts on each key, and measure the time between them. Doing this usefully would require scanning keys much faster than would be necessary for note on/note off, but fast scanning by a dedicated controller is hardly impractical.
    – supercat
    May 28 at 16:46
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VST (and other synth/sampler) 'voices' do not correspond exactly to musical notes.

Sampled piano instruments typically use a number of underlying voices per keyed note - as well as the basic sound of the string vibrating, you might get separate samples for hammer movement, damping, and sympathetic resonance of multiple other strings.

The point of those 64 voices is not to allow you to play 64 different notes at once, it's to more convincingly reproduce the sound of the ten or so you might reasonably play at once, where each note requires multiple voices.

So, it's possible your MIDI device does have a limit on how many simultaneous held down keys it can detect, but that doesn't mean it won't effectively use the available voices on the VST instrument

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