The hardness of the keys on a keyboard is the amount of resistance they provide when pressed.
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Unweighted. Very low rigidity: the keys literally "fail" under the fingers. Found mostly in entry-level keyboards; this is due to the fact that unweighted mechanics are inexpensive, but the low pressure resistance makes it difficult to select the optimal pressure and control the dynamics of the sound.
— Semi-
weighted. Keyboards with medium resistance — not as high as on weighted keys, but noticeably higher than on unweighted ones. This option is considered optimal for active keyboards (see "Mechanics"): at a low cost, it gives quite good responsiveness and, with a minimum skill, allows you to accurately control the pressing force.
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Weighted. Keyboards with high resistance, which is comparable to the resistance of classical piano keys. Note that high effort in this case is an advantage: it allows you to bring the response of the keyboard as close as possible to the response of a classical piano and makes it easier to control the pressure and dynamics of the sound. Actually, by definition, all hammer-action models are made weighted (see "Mechanics"), but among active keyboards this option is rare — due to complexity and high cost.
The ability to programme additional keyboard controls — buttons, pads, faders (see above), etc. — assigning them one or another function at your discretion. This feature allows you to optimally adjust the instrument to your needs and preferences. Note that the programming method can be different: most often you need to change the settings through a computer, but in some models this can also be done using built-in tools.
