Polyphony
The number of voices supported by the digital piano — more precisely, the maximum number of voices that the instrument can play at the same time.
This parameter should not be confused with the number of notes that can be played simultaneously on the keyboard. The fact is that in many timbres, several voices (tone generators) are used for each note at once — this is the only way to achieve a more or less reliable sound. Thus, the required number of voices can be many times higher than the number of notes — for example, the simplest chord of 3 notes may require 9 or even 12 voices. In addition, tone generators are used to play auto accompaniment parts and built-in songs (see below), and here the number of voices can already be measured in tens.
In light of all this, polyphony of less than 90 voices is typical mainly for relatively simple and inexpensive instruments that are not designed for complex tasks. The smallest number found in modern digital pianos is 32 voices. It is desirable for a more or less solid instrument to have at least 96 voices, and in top models this figure can reach 256.
Built-in timbres
The number of built-in sounds provided by the Digital Piano.
Despite the name, digital pianos are extremely rarely designed to imitate the sound of only a piano — the electronic hardware allows them to provide other timbres of sound. In addition, even the piano has its own varieties — for example, among the grand pianos there are 6 main classes, from large concert to miniature. So the built-in sounds can cover different kinds of pianos, as well as other instruments and sound effects.
The abundance and variety of timbres in digital pianos as a whole is not as great as in synthesizers, however, in this category there are very “charged” models, with a hundred timbres or more (in the most multifunctional, this number can exceed 900). However, it is worth specifically looking for a “multi-instrumental” model if you do not intend to be limited to the sound of the piano and would like to have more freedom of choice. It is worth remembering that a specific set of timbres can be different.
If the instrument is bought exclusively as a piano, then here, on the contrary, it is worth paying attention primarily to solutions with a small number of timbres. Such models are not only cheaper than "universals" — they can also sound better (due to the fact that there are few timbres and the manufacturer can carefully approach the sound quality of each built-in "instrument").
Accompaniment styles
The number of Auto Accompaniment Styles (see above) originally stored in Digital Piano memory.
Different auto accompaniment styles differ from each other in the same way that different melodies differ from each other — in tempo, time signature, rhythmic pattern, set of instruments used, etc. Accordingly, the more styles initially available in the instrument, the wider the choice of the musician and the higher the probability of finding the option that best suits a particular situation. However even numerous styles does not guarantee that among them there will be a suitable one; in addition, we note that with the same number of styles, their specific set in different instruments can also be different. However, custom styles can be provided for this case (see below).
Summarizing, we can say this: if you plan to work intensively with auto accompaniment, in addition to the number of styles, it will not hurt to clarify their specific range.
Arpeggiator
The presence of an arpeggiator in the design of a digital piano.
The arpeggiator is able to decompose a chord taken on the keyboard into separate notes and play them sequentially, one after another (in the arpeggio technique — hence the name). Using an arpeggiator can be more convenient than playing notes by hand for a variety of reasons. Firstly, such a system works very clearly: notes are played strictly at a given tempo and sequence, with a given duration and interval. Secondly, only three notes are enough to recognize a chord, and the number of notes issued by the arpeggiator can be much larger. Thirdly, the executed notes can be supplemented with various effects or even a full-fledged accompaniment; many instruments allow you to create simple, but quite full-fledged melodies due to the arpeggiator alone. Although, of course, the specific features of this function may vary, it's ok to clarify them separately.
Modulation controller
The presence of a modulation controller in the design of a digital piano.
This controller allows the musician to use various techniques related to changing the volume of the sounding note — for example, vibrato with alternating peaks and dips in volume, or individual “bursts” of volume, etc. At the same time, the musician himself controls the speed and amplitude of changes — with the help of a lever, wheel or other similar control element.
The modulation controller can give a performance extra "liveness" or specific coloration, and is also used in some artistic techniques.
More features
Additional features and sound customization options provided by the instrument in addition to those listed above. In this paragraph, usually, various original proprietary technologies and solutions are indicated; the specific meaning of these functions is best specified in the documentation for the tool.
