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I’m going to buy a digital piano, I’m a classical pianist, so I would like to know will 128 polyphony be enough to play everything like Rachmaninoff or Liszt, because they have a lot of notes?

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    I recommend getting the best feel/action that you can afford and whatever that is will come with enough polyphony to get by on, if not much more. Assuming the digital is for practice and not performance, the interface with the hands/fingers seems more important than the one with the ears/listeners – Todd Wilcox Sep 26 '20 at 17:22
  • Can someone clarify what this question is about? What is polyphony in this context? What does 128 mean? I'm not sure that the [polyphony] tag is being used as intended here. – Bladewood Sep 28 '20 at 2:04
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    @Bladewood polyphony in this context is "how many sounds/samples the device/digital piano can play at the same time." An extreme example is a toy piano which may only play 1 note -- usually, the first key pressed -- even if multiple keys are pressed at the same time. – Andrew T. Sep 28 '20 at 6:20
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There's no simple yes or no answer to this - it depends on how smart the polyphony recycler is.

Dumb devices will simply steal the oldest note.
Smart ones will steal 'the one least likely to be noticed' by quite a complex algorithm I'm not at liberty to divulge.*

The difference between the best & worst is most noticeable if you hold down the pedal, bang a good loud couple of bass notes in a low octave, then tinkle away gently on some top end. See if the bass suddenly vanishes at an inappropriate moment, or appears to die away at the correct rate.

Some devices will only steal once all notes have been used, so with 88 keys even 'dumb' devices may not appear to steal. Unfortunately, that algorithm is poor on repeated 'same notes' as they don't build up resonance properly.
Smart devices also add their own sympathetic resonances by gently adding in notes & harmonics you didn't actually play - same as a real piano with the pedal down.

*My actual working knowledge of this algorithm is now also 20 years out of date, but I'm still under NDA.

Additionally, as a 'shopping guide', all these things are built to a price - any series/family from each manufacturer will fall into a price bracket, for a specific market segment, with several models in each series. All manufacturers have a series in each bracket. Each price increase in a series introduces better features [or sometimes just better finishes, watch out you're not paying extra for a finish you didn't need], but if you really want the closest thing you can get to a real piano, you're looking at the top model in the top series from each manufacturer.
The really good stuff does not come cheap.

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    For recycled note: along with age, you also factor velocity and avoid outer notes? You are under NDA, but can you tell if it is much more complex than that or around that complexity? Still naive? Use equal-loudness contours perhaps? – user1079425 Sep 26 '20 at 21:00
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    thank you for this excellent answer. i always just assumed that "128" would mean 128 keys could be pressed at once, which seems pretty silly if you only have 88 keys! (and i'm thinking of really old keyboards where you had 4 or 8 and it was obvious when you hit that limit) – Michael Sep 27 '20 at 2:03
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128 is the theoretical maximum that's possible at all with any single MIDI-based instrument, because there are only 128 different notes you can have at all. It's even more limited since the piano specifically has only 88 keys, so even if you play with pedal and strike all the keys, it won't even get to use all the polyphony it technically could.

So, yes, unless the piano uses a stupid greedy note-steeling algorithm as mentioned by Tetsujin, 128 will be plenty enough for piano. The only way it could be not enough is if you use a sequencer and address multiple instrument sounds at once, but nowadays that's pretty irrelevant – just use a DAW with recorded audio for that kind of stuff, not multichannel MIDI.

Generally note that modern digital pianos use a mixture of wavetables, full-length samples and physical modelling, which means that the number of polyphonic voices is not really a fixed number at all anymore. What they mean to express with “polyphony 128” is likely just that it's impossible to get this instrument to the limits of its polyphony.

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  • The 'good ones' are 256 these days, plus all the spatial sampling & calculation, round-robin, key-off, wooden soundboard resonators… yada yada. If you've got 20 grand (£) to spend, it's all yours ;-)) You are paying at least half of that for a full wooden piano action with everything but the actual strings, but you get what you pay for. – Tetsujin Sep 27 '20 at 14:37
  • @Tetsujin a figure like 256 that's mostly marketing buzz. Really properly good algorithms don't have any limit hard-coded at all, but instead dynamically allocate whatever is needed. Then just stuff in generously sized processor power (which is cheap nowadays), and the “true limit” before you get buffer underflows will probably be thousands of voices – but is anyway impossible to reach. – leftaroundabout Sep 27 '20 at 14:44
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    Admittedly. my info is 20 years out of date, but I used to actually make these things - or at lest the demos & styles inside them. I worked in the R&D dept, & am [was] fully aware of the exact technical constraints, hence the smart algorithms that have to be employed so you can't actually ever hear when you run out of poly. It used to be a lot tougher when even the good stuff was only 32 or 64, but I can't see them doing away with all that R&D just to 'fluff' their audience. Bear in mind $1 in the factory is $10 on the street, so costs have to be very carefully managed. – Tetsujin Sep 27 '20 at 14:56
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    No-one is going to throw an A12X Bionic into one of these things so you never run out of processor. We used to joke that half of them ran on the same chips as washing machines, [which is, to all intents & purposes, true] – Tetsujin Sep 27 '20 at 14:57
  • If you model every string, not key, in the piano you'll end up somewhere around 230 voices. From this point 256 kind of makes sense. The idea about playing multiple samples for the same key and stopping the least recent one doesn't really make sense except if you deliberately want to sabotage your own product. – ojs Sep 27 '20 at 19:40

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