This article is from the Digital Pianos FAQ, by Isako Hoshino rmmpfaq@yahoo.com with numerous contributions by others.
As for *manufacturers*, they usually differ in:
(1) how they sampled or generate the sounds,
(2) key action design,
(3) sound output design,
(4) overall appearance.
Thus each company's product line has a distinctly different feel and
sound. There are many makers out there. (In alphabetical order)
Baldwin, Casio, Kawai, Korg, Kurzweil, Roland, Samick, Technics,
Wersi, Yamaha, to name a few. The best way to decide what these
differences mean to you is to go to a local dealer and try out the
different brands.
Usually, the main differences between various models within the *same
maker* are in:
(1) the weighted key action (how the keys feel),
(2) amplifier power,
(3) number and size of speakers,
(4) number of voices (piano and non-piano sounds),
(5) polyphony (how many notes you can play simultaneously),
(6) the miscellaneous "gadgets" (like sequencing
capabilities, metronome, etc.)
In general, the more money you shell out for a digital piano, the more
closely it imitates a piano and better sound. The difference between
a low-end model and a mid-range model is usually pretty dramatic.
Some low-end models do not have all 88-keys. Some may not even have a
sound output system (you basically play it through your stereo
speakers or use headphones). The difference between a mid-range model
and a high-end model is mostly in the "gadgetry" department and in
amplifier power; most of the key elements don't vary a whole lot. The
majority of the digital piano market is in the mid- price range, and
that's usually good enough to keep most people happy.
 
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