How is an instrument tuned?

To tune any two instruments, the sound waves from both of them must be at the same frequency. If the frequencies differ very slightly, the two sound waves interfere, making another sound wave that undulates in volume or 'beats'. The beat frequency is the number of volume undulations heard per second. It is found by subtracting the lower frequency from the higher one. When two instruments are in tune, the beat frequency should be zero. This is an extremely useful tool for tuning instruments accurately by ear.

Most people can usually tell whether an instrument is in tune or not without knowing the underlying science.

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