Frequency
Definition
The rate at which a sound wave completes one full cycle per second, measured in Hertz (Hz). Frequency determines the perceived pitch of a sound — lower frequencies produce lower pitches, higher frequencies produce higher pitches.
In Simple Terms
How fast a sound wave vibrates, measured in Hertz. Low numbers (50 Hz) are deep bass you feel in your chest. High numbers (10,000 Hz) are bright, airy sounds. This is what determines the pitch you hear.
In Practice
The note A4, the standard tuning reference, vibrates at 440 Hz. A kick drum produces most of its energy between 50–100 Hz.