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?
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 ;)
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.
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
