A synth maps a note number to frequency and keystroke velocity to amplitude before any sound is generated

Sound synthesis begins with a musician’s gesture — pressing a key, clicking, or moving a controller — which produces control information rather than sound directly. The two most fundamental pieces of control information from a keyboard gesture are the note number (which key) and the velocity (how fast/hard it was pressed). The synthesizer converts note number into a frequency f and velocity into an amplitude A. This (f, A) pair is enough to drive most popular synthesis algorithms, including the wavetable oscillator. Understanding this gesture-to-parameter mapping explains why the same synthesis engine responds to any controller: the controller only has to emit note+velocity, and the engine handles the conversion. It is also why velocity layers and velocity-driven timbre changes are possible — velocity is a first-class control signal, not just loudness.

Examples

MIDI note 69 -> 440 Hz; velocity 100/127 -> a higher amplitude A than velocity 40/127. A pad patch might additionally route velocity to filter cutoff so hard hits are brighter.

Assessment

A learner presses a MIDI key. Name the two pieces of control information a keyboard gesture provides and state which synthesis parameter each is mapped to. Why is (f, A) sufficient to trigger a basic oscillator?