Velocity Davenport IA

The loudness of the note depends on how hard you strike the key. But even in the piano, quite a lot of technology (in the form of carefully balanced levers) goes into producing that effect.

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Velocity

If you’ve ever played a piano, the process seems perfectly natural: The loudness of the note depends on how hard you strike the key. But even in the piano, quite a lot of technology (in the form of carefully balanced levers) goes into producing that effect. Other keyboards, such as organs and the first generation of synthesizers, don’t respond in that way. Play lightly, play hard — it makes no difference.

Just about all synthesizer keyboards today respond the way a piano does. There will be subtle differences, but the speed with which the key travels downward is sensed by a mechanism of some sort, and the information coming from the sensor is used to affect the sound of the synth.

The speed of the key as it descends toward the keybed is called its velocity. Each key has its own velocity sensor. And because just about all keyboards transmit MIDI, the velocity data is always encoded in the form dictated by MIDI. MIDI defines messages called note-on and note-off, and each note-on message includes velocity. (Note-off velocity — the speed with which the key is allowed to rise at the end of the note — is also defined by the MIDI Specification, but it’s rarely used.)

Because the velocity is embedded in the note-on event, the velocity of a note can’t change while the note is sounding. The value transmitted by the velocity sensor remains the same from the start of a given note to its end. Manufacturers of consumer keyboards sometimes blur this distinction by referring to velocity as “pressure.” MIDI defines a separate type of data called pressure, or aftertouch. When a keyboard senses pressure (not all of them do), you can send a control signal by pressing down harder after the key has reached the keybed. But that control signal has nothing to do with velocity.

MIDI defines velocity as a data type that can have values ranging from 1 to 127. A velocity of 1 is extremely slow (produced by very light playing), and 127 is extremely fast (produced by very hard playing).

USING VELOCITY TO CONTROL SOUND

The most common use of velocity is to control the loudness of the notes. As on a piano, when you play harder, the notes will be louder. On a synthesizer, this is accomplished by using velocity to modulate the amplitude of the audio signal. If you roll up your sleeves and do a little voice programming, you’ll probably find a parameter called VEL or Velocity in the Amplifier, AMP, or VCA area of your synth. If you turn this parameter down to zero, the velocity-to-loudness effect should go away: All notes should be equally loud.

If you listen closely to a piano, you’ll hear that the louder notes also have more sound energy in the upper frequency range. In other words, they’re not only louder, they’re also brighter. This effect is modelled in most synthesizers. If your synth has analog-type lowpass filters, you’ll find a parameter with which you can control velocity modulation of the filter cutoff frequency. When the velocity value is higher, the filter cuto...

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