the fundamental of every note in hertz · equal temperament, A = 440 Hz
Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.
Three sizes in one archive — from a sheet on the fridge to a poster on the wall.
Frequencies computed from A = 440 Hz (ISO 16:1975) in equal temperament; to one decimal below 1000 Hz, whole above. Bands are ISO 266:1997.
The ISO 266 series of preferred frequencies — 31.5 · 63 · 125 · 250 · 500 · 1000 and on up to 16 kilohertz — is a thousand halved. A thousand hertz sits 21 cents above B5, and half of it sits the same 21 cents above B4. The octave bands every spectrum analyser is divided into are one note, ten times over.
For anyone mixing the consequence is plain: "cutting a kilohertz" means cutting B — and not in one instrument but in all of them at once. The names 63 and 31.5 are only convenient roundings of 62.5 and 31.25: the series is named in round numbers and built by halving.
The second thing the same formula shows: a semitone is always 5.9 per cent, never a fixed number of hertz. On the lowest band of the series it is 1.9 hertz wide, on the highest it is 951. That is why the width of an equaliser band is set in octaves rather than hertz: a hundred hertz covers two octaves at the bottom and a tenth of a semitone at the top.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 7 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.
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