Why you hear a note that isn't there: the missing fundamental
30seconds
Play only 220, 330 and 440 hertz and most people hear a note at 110 hertz — a frequency that is not in the sound at all. This is the missing fundamental: the brain reads the repeat rate of a wave, not which frequency is strongest.
Switch harmonics on and off in a live waveform, see why the pitch holds when the bottom note is deleted, and meet the same trick in telephones, small speakers and pipe organs.
Deep dive · 5 min
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