It seems like it should be pretty simple to just record the sound of a concert grand and play it back on a speaker. In fact, that’s what we do for studio albums. Is it the sustain pedal that causes the main difference in sound between an acoustic and a digital? Or would playing both without the pedal still sound different? I actually own a pretty sophisticated digital piano, the Kawai CA49, and it sounds a lot better than cheaper pianos, but I probably wouldn’t be able to tell the difference between it and an upright acoustic.
In: Engineering
The big difference is due to how pianos make sounds. The action of the hammer striking the strings at different velocities will cause the strings to vibrate differently and cause subtle changes to the note. Unless you sampled most every key at a variety of known velocities and could play them back correctly, you’re going to lose out on those subtleties.
The challenge is in all the effects of the body of the piano and sympathetic vibrations. Lets break the sounds down a bit.
First, take any single key, that has to have a hundred+ velocity (how hard you hit) variations to sound convincing. A single key press vibrates the soundboard and wood in unique ways per note. It also gets sympathetic vibrations on other strings.
It starts to get complicated when you add additional notes because there are ways those vibrations interact to boost or cancel each other. Wood isn’t perfectly predictable. It was a living thing with different densities across its grains. There is probably even some effect of the air acting as a mild natural compressor, though I think that must be subtle.
And then you multiply that by those 100+ states of velocity, across how ever many notes you hit, each with their own velocity.
So you get quickly to a point where the amount of samples in play would be quite a lot. There are ways it can be algorithmically approximated, and Ive heard recent ones that are pretty convincing.
And all of that is an easier instrument because notes in a piano forte are hit one way. Guitar, for example, you can hit the strings in dozens of discernibly different ways.
The sound of an acoustic piano depends on how (hard, fast, …) you hit each key. The simplest digital pianos entirely neglect this (and always play the same sound).
For a bit better digital pianos, some might have a few pre-recorded options to pick from (which isn’t quite the same as the continuous range in a real piano), and the even more advanced models might just model the sound alterations in real time for a full range of adjustments.
With modern digital pianos, a sufficiently advanced model probably starts to be sufficiently indistinguishable for practically all uses. It certainly will perform better than most acoustic pianos. (Which is also why the second-hand value of basic acoustic pianos dropped to zero a decade or so ago where I live.)
I have a CA49 too, and what others have said about digital sampling is wrong. The CA49 has been sampled using the best grand pianos, at different actions, with sophisticated software that’s only gotten better over the years.
The sound that the CA49 (and other similar digital pianos) produce is impeccable, but it sounds different to an actual acoustic piano because of the physical differences in the construction. The CA49 is just a keyboard on a fancy stand outputting sound from pretty good speakers. In fact, plug in headphones and it sounds even better. But, an acoustic piano has vibrating strings with, most importantly, tons of wood that acts as a soundboard. A soundboard is a way to amplify music based on the specific properties of the wood. Without it, it will just sound totally different and spatially different. To put it simply, while the sound waves might be the same, the way they bounce around the room on different materials is completely different and changes how you’re going to experience it. There are also other differences such as secondary strings vibrating when a string is played, which is probably picked up in the sampling but can’t be replicated when the sound comes from a single speaker instead of several different strings in the piano.
I mean they do make pretty flipping good electric pianos, and even guitar amps (see line 6) but the fundamental way you’re making the sound is different – basically an oscillating string vs a loud speaker (paper cone and a magnet).
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