A while ago KimC said "One thing I wonder about, though, Don, is that if tuning wasn't really standardized, how do we know that Mozart's Ab wasn't Beethoven's F#?"
and Don Firth said "When Vivaldi or Mozart or Beethoven specified what keys they wanted their compositions to be played in, they had specific sounds in mind."

I won't repeat it all here, but in the One-Chord Songs thread there was a lot of music theory (some may pass over the head of some, but that's OK!) about "Just" and "Tempered" intonations (there are other threads about this theory too.)

Don's comment is interesting, because it skims over the real reason WHY they did this. The "Just" system as the referenced thread elaborates, means that for instruments tuned to say C Major in "Just" Intonation, playing in other keys means that the notes are "out" for any keys other than the "base" key that you tune the instrument to.

"Equally Tempered" Intonation tuning did away with all that, with both positive and negative results:

Positive; all instruments could now play with all others in any key without retuning (other than for purpose of absolute pitch - the relative pitches were now all in agreement!). The Well Tempered Clavier was the big demonstration piece for this - which is WHY is was composed! It was a BIG HIT of its time!

Negative; the particular sounds of certain keys (sad, happy, etc) relative to the original "Just" tuned base key now disappeared entirely, as the relative distances between notes was the same in ALL keys. This is what is really meant by Don's remark, perhaps more than he conciously intended - although I don't know (and don't care, it really doesn't matter to me cause I was not trying to insult him!) his level of experience in Classical Music Theory! :-)

I don't know of too many electronic tuners that can be set to pure "just" intonation - if anyone does, I'd like to know! - they are all in "Equally Tempered" intonations tuning!

So --- depending on how old the particular Tradition is   :-) (see the other thread!) a "Traditional Musician" perhaps could be performing in "Just" - a relatively easy thing to do on an unfretted string instrument or the human voice - it merely relies on his sense of "Perfect Pitch"! Playing along with such a muso with "Equally Tempered" instruments would be "interesting" to say the least... and everybody else would try to claim that he was "wrong"!

Interestingly "Traditional" singers may NOT be in Pure Modern "Equally Tempered" Intonations - there were countless "Temperings" before the mathematically based modern "Equally Tempered" (often confusingly abbreviated to merely "Tempered") system swallowed everything else - some still exist on this planet! (The Orient - Africa, etc)

A comment was made about 19C "collectors" putting collected tunes into particular keys - they were also struggling with the "Temperings" and the Modalities (Also see the referred thread!) - classically trained musos believed only in "Equally Tempered" - Folk Temperings were only finally killed off by the spread of the "Equally Tempered" Piano Accordion! Other free reed Squeeze Boxes added their nails to the coffin too... Pianos were tuned "Just" or some form of "Tempered Just" until Portable "Equally Tempered" Tuners were available. Most people (Folkies!) normally tuned to a piano. Orchestras traditionally tuned to the oboe.

Of course I doubt that the original muso that started off this thread was aware of the above ... :-) the discussion has already gone over that ground!

Pardon Me for repeating this...
QUOTE
Came across an interesting reference in Irish Traditional Music. Seems that it was considered bad manners to advise a fellow session fiddle player that he was out of tune. The accepted courtesy was to say "Sean, can I borrow your wee fiddle for a moment to try out that tune you was playin'?"

Then play a tune, and stop and say "I'm sorry Sean, the thing's gone out of tune now while I was playin' it"

and then retune it... and pass it back :-)
UNQUOTE

Robin