Two slightly different tones played together create a slow throbbing effect called beating.

The longer version

Two tones close in rate drift in and out of step. When their pressure peaks coincide they reinforce, and a moment later one has slipped half a cycle ahead so they cancel, producing a slow swell and fade whose rate equals the difference between them.

Small differences give a slow throb, larger ones a rough buzz, and beyond a certain width the ear hears two separate tones instead. Tuners use the effect directly: they listen for the pulsing to slow and stop as two strings are brought into agreement. The same interference appears whenever two steady sources of nearly equal rate overlap in one space.

Where this entry sits

Sound and Music gathers facts about how vibrations move through air and water, how ears turn them into meaning, and how instruments and notation shape what listeners hear. Expect echoes, pitch, volume, acoustics, and the odd silence in between. The full list sits on the Sound and Music page, where every entry is listed in order.