In 19th century, spacing the 12 semitones equally in the octave allows all keys to transpose {equal temperament tuning}, though different instruments tune to different keys. In equal temperament, all keys sound the same.
19th-century music scales can have pure fifths and pure thirds {just temperament} {just intonation}, instead of only pure fifths.
As musical instruments improved in 16th century, scales used fixed and unequal intervals between notes {meantone}. To make pure third, each fifth added equal frequency ranges. However, this created quartertones in higher keys. In meantone, keys have different sounds.
In 16th century, meantone changed to allow instruments to play full chords in all keys {well-tempered}. In well-tempered scale, keys have different sounds.
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Date Modified: 2022.0225