Do the EDO and TET acronyms mean the same thing?

Question

In the context of dividing an octave into n intervals, I understand n EDO to mean n Equal Divisions per Octave and n TET to mean n Tones Equal Temperament. Do the EDO and TET acronyms mean the same thing or is there some subtle difference?

Answer 1

In addition to TET referring to temperament, which does not make sense for e.g. 11EDO, it also differs in that it does not specify what range these notes divide equally, whereas EDO explicitly states that it's the octave. Now, the vast majority of commonly used tuning systems do use the octave as their foundation, but not all, notable counterexamples being the (tempered) Bohlen-Pierce scale (13EDT) and Wendy Carlos' α (9EDF), β (11EDF) and γ (20EDF) scales. The latter can't really be considered temperaments at all, but the Bohlen-Pierce scale absolutely is a temperament: in much the same way 12EDO tempers the Ptolemaic system of just intonation (5-limit with octave equivalency, i.e. the set of intervals in the range [1,2[ which can be constructed as integral frequency ratios using only the numbers 2, 3 and 5), Bohlen-Pierce tempers the odd 7-limit with tritave equivalency (the set of intervals in the range [1,3[ which can be constructed using only the numbers 3, 5 and 7). So, one might well interpret “13TET” as Bohlen-Pierce, which is very different from 13EDO.

I personally think that non-octave based scales are actually more promising for making new microtonal music that's practical to play and somewhat easy to grasp from listening, in particular if you go to the 11-or even 13-limit, which gets extremely difficult (see Ben Johnston) to do with all the octave-derived pitches available (giving the factors {2,3,4,5,6,7,8,9,10,11}, but much more tractable when the ratio 2 is out and you only have {3,5,7,9,11}. Bohlen-Pierce itself is in fact arguably a bit too tidy, making it hard to build up any sort of direction-defining dissonance.

Answer 2

In practice, they are the same thing, but they show a slight theoretical distinction in their "purpose", which is outlined quite well here http://xenharmonic.wikispaces.com/EDO+vs+ET

EDO indicates that an octave is being subdivded, and nothing more.

A temperament is essentially an attempt to "square the circle", and get intervals that transpose well but also provide a reasonably effective approximation of "pure" (or "just") intervals (whole number frequency ratios). It is an exercise in compromise. Some (most?) temperaments rely on other methods than subdividing the octave equally: so you can have a temperament that is not equal (like meantone temperaments for example), and you could also have an equal division of the octave which doesn't really approximate any pure intervals. In fact, more of them don't.

In that sense, you could argue that, say, while 12TET/12EDO, 19TET/19EDO, 31TET/31EDO etc. are exactly identical, 11TET doesn't really exist, as 11EDO isn't really a "temperament" at all; it doesn't make any attempt to be an approximation to natural whole number frequency ratios.

That being said, if you say 11TET, it's never going to cause confusion, but 11EDO is more "technically correct".

Answer 3

The main difference between an EDO and an ET is whether you declare it to represent a JI system well. For example, you could call 9edo an ET because it maps nicely to 7-limit intervals.

Answer 4

In addition to the points already made, there is the issue of the word "tone." We already have this problem with twelve-tone equal temperament because in most contexts the twelve equal divisions of the octave are called semitones, not tones. In fifty-three-tone equal temperament, at least when it's used to approximate just intonation of traditional harmony in traditional staff notation, a semitone can be anywhere from three to six of these divisions and a tone can be eight or nine of them. It's confusing to call the divisions "tones" in this context.

By the way, the fact that "n-tone equal temperament" is properly written with a hyphen and "n divisions of the octave" is not explains why (e.g.) 31-TET should be written with a hyphen but 31 EDO is not.