Tone Generator

What the controls do

The frequency is in hertz — cycles per second. Type a number or drag the slider, which is logarithmic, so an octave takes the same distance whether you are at 100 Hz or 10,000 Hz. You can change it while the tone is playing and hear it slide.

The wave shape changes the character. A sine is the pure tone with nothing else in it; square and sawtooth add harmonics and sound much brighter and harsher at the same frequency; triangle sits in between. For testing equipment, a sine is usually what you want.

What it is useful for

• Finding a rattle: sweep slowly upward and listen for a buzz that appears at one frequency and then goes.
• Checking that a speaker or headphone driver reproduces low or high notes at all.
• Tuning by ear against a reference — 440 Hz is the usual A above middle C.
• Telling whether a hum in a room is from mains power, by comparing it with 50 or 60 Hz.

Please be careful with this one

A pure tone concentrates all its energy at one frequency, so it can be genuinely loud when music at the same volume setting sounds moderate. High frequencies are the worst for this, because they are easy to under-hear until they hurt. Start quiet, raise slowly, keep it short, and stop the moment it is uncomfortable.

This page starts at 25%, ramps the tone in rather than switching it on, and caps its own output well below full scale — but it has no idea what your volume control, amplifier or headphones are doing, and no decibel figure appears anywhere on this site because a browser cannot know.

If you want a tone through one speaker at a time, use the Speaker Test. For a sweep across the range by ear, the Hearing Range Test; for a click at a tempo, the Metronome.