Where the name actually came from
The black keys are called sharps and flats. That naming came from the keyboard layout, and the layout came from tuning systems that were in use long before equal temperament existed. In quarter-comma meantone, the standard tuning for sixteenth and seventeenth century keyboard instruments, fifths are narrowed so that major thirds land close to just intonation. The accidentals then split: an F sharp key is not quite the same pitch as a G flat key, and the keyboard has to carry two slightly different accidentals for some note names.
A fixed-pitch keyboard must decide how many accidentals to print, and meantone builders typically printed one set for the ascending sharp side and a slightly different one for the descending flat side. In those layouts the accidentals landed on the raised keys. When equal temperament made all accidentals identical, the physical keys did not move, because the layout was already there. The labels went with the positions.
The raised position is also a mechanical answer. Half-steps sit in the gaps between wider whole steps, and a keyboard with two sizes of whole step needs the short gaps to be visibly distinct. That is packaging, not tone.
What equal temperament actually equalises
Equal temperament divides the octave into twelve equal semitones of exactly 100 cents, totalling 1200. That is the whole definition, and the consequences follow arithmetically. A fifth becomes 700 cents. A pure three-to-two fifth is 701.955, so every fifth in equal temperament is 1.955 cents narrow. A major third becomes 400 cents. The pure five-to-four third is 386.314, so every equal-tempered major third is 13.686 cents wide.
| Interval | Equal temperament | Just intonation | Error |
|---|---|---|---|
| Perfect fifth | 700.00 cents | 701.96 cents (3:2) | 1.96 cents narrow |
| Major third | 400.00 cents | 386.31 cents (5:4) | 13.69 cents wide |
| Minor third | 300.00 cents | 315.64 cents (6:5) | 15.64 cents narrow |
| Octave | 1200.00 cents | 1200.00 cents | Exact |
The payoff for those errors is that all twelve keys work. In just intonation a chord transposed up a fifth is a genuinely different chord, because the ratios that make it consonant have changed. In equal temperament it keeps its colour, so an arrangement can move between keys without the harmony shifting underneath it. For a producer working across an album, that consistency is worth more than the purity of any single chord.
- Fifths are 1.96 cents narrow, which is close to the limit most listeners can match against a reference.
- Major thirds are 13.69 cents wide, which is well past it. This is the audible cost of the compromise.
- The residual roughness of an equal-tempered major triad is the third error and the fifth error heard together.
The wolf interval and what came before
Before equal temperament there was the wolf: the one fifth in the circle pushed far enough out of tune to close the loop. Quarter-comma meantone has twelve usable fifths and one that does not, sitting near 737.6 cents and roughly 35 cents wider than the rest. Pythagorean tuning stacks pure three-to-two fifths without correcting for the comma they accumulate, so its error grows all the way round. Both give a keyboard that is consonant in the keys you use and plainly out in the one you avoid.
This is why equal temperament is described as a compromise rather than an improvement. It does not correct anything. It spreads the error evenly, so no interval is right and no interval is catastrophic. Simon Stevin had proposed equal divisions of the octave mathematically by around 1585, and Andreas Werckmeister published temperaments in 1691 that circle close to the modern one, with the generalisation to all keys arriving gradually through the eighteenth century.
Higher divisions exist for the same reason. Fifty-three tone equal temperament places the fifth 0.06 cents from pure and sounds noticeably purer, but it needs fifty-three keys per octave and a workflow no DAW assumes. Twelve tone is not a law of nature. It is where the improvement stopped paying for the inconvenience.
What it means in a session
The measurable consequence is specific. A recorded chord does not change when you transpose it in equal temperament, so a mix decision made in one key holds in every other. A piece written in just intonation will not survive transposition, and its character will move with it. Write the same chord both ways in a DAW and you can hear the whole argument in an afternoon.
Test it blind before believing a claim in either direction. Record the same major triad in equal temperament and in a sixth-comma meantone, level-match them within a fifth of a dB, and switch at matched loudness. Any difference lives in the third, it will be small, and neither version is obviously correct. Keep whichever suits the arrangement.
The naming is the part worth keeping straight. Sharps and flats are the vocabulary of one tuning tradition, not properties of pitch. What the ear responds to is the relationship between frequencies.
The bottom line
The black keys are named for where accidentals fell in sixteenth-century meantone layouts, which is a fact about a tuning system rather than about those pitches. Equal temperament is a compromise that spreads error evenly so every key works, not a correction of anything, and it is worth judging by ear rather than by its reputation.
Hear the same chord in two tunings
432Hz MASTER moves the whole production by one ratio, so you can compare a chord at 432Hz against the same chord at 440Hz with the interval relationships intact.
Frequently asked questions
Why are they called black keys?
The name comes from their physical position and from the accidentals that landed there. In meantone and werckmeister layouts the accidentals sat on the raised keys, so those keys became known as sharps and flats. It describes a keyboard, not a pitch quality.
Is equal temperament more accurate than just intonation?
It is more consistent, not more accurate. Equal temperament is out by about 14 cents on a major third, which is far from pure. What it gains is that the error is the same in every key, so a chord keeps its colour when you transpose it.
What is the wolf interval?
In temperaments before equal, the circle of fifths had to close somewhere, and the interval that closed it was left badly out of tune. In quarter-comma meantone the wolf sits near 737 cents, roughly 35 cents wider than the other fifths, and it is audible on every keyboard that still uses it.
Does 432Hz change any of this?
It sets the reference pitch, nothing more. Transposing from 440 to 432 changes every frequency by the same ratio and leaves the relationships between them untouched, so the temperament debate is unaffected.