[linux-audio-user] in tune - stupid thread

[tim hall]

Last Sunday 19 December 2004 21:29, John Anderson was like:
> On Sun, 2004-12-19 at 18:55, Russell Hanaghan wrote:
> > Fact is, it is impossible to tune an acoustic guitar
> > "perfectly"...Invariably, when you have it tuned so an open G chord
> > sounds spot on, an open A or even C will be a tad off. And the same
> > applies to the inverse of course.  This all due to a general lack of
> > adjustment for intonation on acoustic axes.
>
> Actually, even guitars with adjustable bridge saddles won't be perfectly
> in tune with themselves, except for octaves, 4ths and fifths which are
> close enough that one can't really hear the difference. This is because
> the frets are in the wrong place in relation to the overtone series
> (pl). This applies to any instrument that has fixed notes (piano springs
> to mind), and which use the 12-tone equal temperament tuning.

I find I always need to retune between songs in D Major and open E (minorish). 
It is the B string that is particularly difficult, I have a fixed bridge.

My preferred method, which usually gets closest to 'in tune' is to tune the 
bottom four strings by the harmonics on the 5th and 7th frets. Then tune the 
top E to the 7th fret harmonic of the A string. and similarly tune the open B 
to the 7th fret harmonic of the E. This will sound great in open E, but crap 
in D and most other keys because I tuned up on the harmonics. In particular 
the relationship between the G & B string, a major third, sounds wrong.

The best way to approximate for other keys seems to be to tune the G & D 
strings up to match the 3rd fret on the E & B strings respectively. Strictly 
speaking the A should be a tad sharper, the D two tads and the G three, where 
a tad is some fraction (1/3?) of a pythagorean comma. I often find with my 
fixed bridge that I need to flatten the B in some keys. It's the relationship 
between the G & B strings which generally you have to guess at because B is 
at the bottom of the harmonic table and G is at the top.

> It's a long story, so I won't go into detail. Google for Just Intonation
> if you want to know more. It sheds a different light on various
> questions like, where *is* that confounded blue note? Why do major
> chords sound crap on overdrive? What's the deal with barbershop and
> string quartets? Why is D minor the saddest key? If I tune the B string
> by ear to the G string, why is it out of tune with the E string?

Ah, I never thought about major chords sounding crap on overdrive, due to the 
harmonics of the flattenned Maj3rds messing it all up. The Greeks thought 
they were discords, perhaps they used to play a lot of Heavy Metal in the 
classical era? Similarly I am always impressed with the way modern Bulgarian 
choirs can sing diatonic clusters and make them sound wholly harmonic.

cheers

tim hall
http://glastonburymusic.org.uk