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equal temperament

Tuning that splits the octave into twelve identical steps, so every key is equally playable and equally, slightly, out of tune.

The tuning nearly all Western instruments use: split the octave into twelve identical semitones, each the twelfth root of two. It makes every key equally playable, at the cost of making every key equally, and slightly, out of tune. That compromise is what lets one piano play in all twelve keys. Its rival is just intonation.

Learn it: The math behind music

The one-sentence definition at the top is the same one the Theory Aide extension shows as a tooltip inside Ableton Live. Hover any dotted term for its own.