What was the earliest equal temperament system used?

I believe it to be 19edo, used by Guillaume Costeley in Seigneur Dieu ta pitié, in 1558. Was any equal temperament used before then?

7edo is stated in many places to be used in Thai traditional music, but I can't find any evidence of that.

Don't count any piece that only uses octaves (since one-tone equal temperament is dumb).

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    It was recognized fairly early on that the large and small tones of just intonation comprise roughly 9 and 8 commas, respectively, and that the semitones can be three, four, or five of these commas, and that the commas are midway in size between the syntonic comma and the Pythagorean comma (which are already very close in size). This leads to 53-tone equal temperament, but whether or to what extent that knowledge was used, I do not know, and I don't remember whether that was before or after 1558. I think it was probably in the 1600s.
    – phoog
    Jan 27, 2023 at 3:51
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    @phoog The Wikipedia page on 53EDO suggests that it was studied in antiquity, but it doesn't appear to have been put into wide practice until it was adopted in Ottoman classical music.
    – Theodore
    Jan 27, 2023 at 15:25
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    You might look into fretted instruments in the Renaissance. My long-held assumption that equal temperament was a relatively new idea in the time of Bach (enabling the Well-Tempered Clavier to be written in all keys, for instance) has turned out to be false. Apparently lutes (etc.) were tuned in equal temperament long before then out of necessity. But I haven't done research enough to post an answer.
    – nuggethead
    Jan 31, 2023 at 14:26
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    @mathlander yes, I meant to say "major tone."
    – phoog
    Jan 31, 2023 at 22:01
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    @phoog It won't count unless they are specifically nth roots of two. All the steps have to be absolutely equal, but since it is impossible to get that level of precision, there needs to be a written instruction saying that all steps are equal, which is the case in Seigneur Dieu ta pitié. A qualitative instruction like the one you mentioned would count if it specifically states that all fifths must be absolutely equal. Even if no such instruction was written, if it was meant to follow a standard equal temperament system at the time (which I don't think existed before 12TET), it would count.
    – mathlander
    Jan 31, 2023 at 22:46

1 Answer 1


As of 7 February 2023, there is no credible evidence in browser searches on Google (including Google Scholar) that equal temperament of any kind was used previously to 1558, nor is there evidence that 7edo was used in Thai traditional music. There may be something in a print book or a letter tucked away in some music library, but it hasn't been scanned yet.

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