Generate a pure test tone at any frequency from 20 Hz to 12 kHz with sine, square, triangle or sawtooth waveforms. Use it to test speakers and headphones, check the range of your hearing, tune instruments, or find buzzing/rattling in a room. Lower the volume before playing — sustained tones can be loud.
440 Hz is concert A. Most adults hear roughly 20 Hz–17 kHz; high frequencies fade with age.