The technique is most commonly used for sampling accoustic instruments, where the instrument is sampled using several different degrees of emphasis, and the samples are mapped to ranges of velocity values. Some samplers implement velocity switching, in which the velocity value is used to select a sample for playback from a set. Other common uses are to use the velocity information to scale the overall rise and fall times of the envelope (all of the envelope segments happen faster when the velocity is higher), or to open up (move the cutoff frequency higher) a low pass filter more at higher velocities. Both techniques allow the performer to emphasize certain notes by pressing the key more quickly. In synths, velocity is most commonly used to either set the peak level of the attack of an envelope generator, or set the overall volume of the note played. (There are other changes in the note sound of a piano as the velocity varies, but such is beyond the scope of this definition.) In the MIDI standard, a velocity value is transmitted with each note on message. Velocity measurement is intended to simulate the behavior of a piano mechanism a note struck on a piano is louder if the key is struck more forcefully.
A measure of how rapidly and forcefully a key on a keyboard is pressed when the player initially presses the key.
