Can anyone tell me what it is? How do you use it singing or playing the guitar?
"Whenever they's a fight so hungry people can eat, I'll be there. Whenever they's a cop beatin' up a guy, I'll be there . ."
The Grapes of Wrath

RIP Ingmar Bergman
I think it's when you throw your intonation slightly off for a stressed feel. Or you can use say... a quarter step bend to hit a kind of "half-note". I'm probably utterly incorrect, though.
Whole tone: A to B
Half Tone: A to Bb
Quarter Tone: A to the note between A and Bb.

Those are all known as a Tone, a Semitone, and a Microtone, respectively.

Quartertones are not commonly used in Western (America and Europe) music. They do appear in Indian and far Eastern (China and such) music.

Now ask me about the quartertone in the blues!
Tell me about the quarter tone in the blues
"Whenever they's a fight so hungry people can eat, I'll be there. Whenever they's a cop beatin' up a guy, I'll be there . ."
The Grapes of Wrath

RIP Ingmar Bergman
I'm going to assume you understood what I said. If not, I will explain in different words, or at least bold what I said before.

The Blues:

Let's say you're playing a blues in A. Conventional wisdom says to play a C# note during the A7 chord. But a lot of people like to play a C to get that bluesy feel. Why not split the difference? Bend a C up a quarter tone and you get the true blue note, the note halfway between the minor and major thirds.
"microtonal" could also refer to an acute awareness of fine tuning/temperament - There is more to tuning than the imperfectly (unless you've got Feiten, in which case it's much closer) equal temper most guitarists are used to.

A guitar being one of the few fixed-pitch instruments most winds and strings achieve a tuning much closer to just than a guitar - which is why playing a guitar (or sometimes a piano) with an orchestra can be hazardous - they need to be tuned very very well.

Anyway most conscious playing with microtonalism will be the use of quartertones - either to play the blue note or to explore eastern forms.
Here's an interesting discussion from Steve Kimock

"Hi guys! Great thread. Too much stuff to reply to all at once, but I'll get to what I can today.
1. As JonR suggests, most of the work here is just agreeing on definitions.
Following are a couple of definitions that I've settled on for the time being that might help
clear some stuff up.

As regards 12 edo (equal divisions of the octave) being "atonal", that's gonna depend on
your definition of "tonal".

Here's an interesting definition of tonality taken from Owen H. Jorgensen's book
TUNING comprising The Perfection of Eighteenth-Century Temperament
The Lost Art of Nineteenth-Century Temperament
And The Science of Equal Temperament.

The preservation of the psychological feeling of rest during a musical performance when
the tonic key center is reached. In acoustics, the definition of tonality is more specific as
follows: In the just tunings and meantone temperaments, flats cannot be used musically
as sharps, and sharps cannot be used musically as flats. . . blah blah blah
(omitting some info here re: acoustic tonality) Jorgensen concludes:
The more unequal or uneven a scale is tuned, the stronger is its basic tonality.

The physical mechanism of resolution requires all the vibrations to end at the same point.
In the case of the tonic major chord the "unequalness" of the tuning necessary to provide
this resolution is just another way of saying the pitches are in an overtonal relationship.
The nodal point they all end at together being the string terminations, nut and bridge.

As the 12 edo. versions of those same pitches don't satisfy that requirement, they are
by definition atonal.

This is a very narrow definition of the tonal/atonal concept that is borrowed from piano
tuning and vibrating string physics as it relates to music.
Obviously not the standard musical definition from the perspective of conventional music
theory (which necessarily deals with its harmonic relationships from the perspective of
the temperament in which they are rendered) but correct nevertheless from the viewpoint
of physical vibration.

2. Harmonic/partial useage and definition.
From my side of the glass, "harmonic" is a musical term, "partial" a scientific term.
I've settled on the "partial" terminology becase it agrees with the use of ratios to
describe musical relationships.
Even tho it disagrees with the interval names, 3rd partial is a fifth, 5th partial is a third
etc. the "musical harmonic naming system" agrees with neither, so for me it's just
less confusing to go with the nomenclature that agrees with the ratios.
I believe that's the conventional wisdom in the majority of the microtonalist community
if there is such a thing. . .

3. The definition of "five limit system": a system limited to tones derived by multiplying
or dividing the frequency of a generating tone by the primes two, three, or five
(namely, perfect octaves, perfect fifths, major thirds, and their compounds and reciprocals).

Anyway, those issues caught my eye as I scanned the thread.
I'm always happy to adopt/discard any definitions for the purpose of clarity, and will
gladly take any side of the debate just for fun.
I'm not married to any of this, I just get a kick out it. . .

A couple of comments that run counter to my own experience in this area were on the
subject of blues intonation.
Re: The use of compound septimal harmony in blues music, specifically the ratio
49:32, the "blue note of the blue note".

Quick story here.
When I practice my fretless instruments, with or without a drone, I frequently check
my intonation with my Peterson as I **** away the hours. While ******* some stock
blues riffs one night I was horrified to notice that I was nowhere near the "5th" I
assumed I was bending to. The lick sounded right, I was hitting the note, but what note?
Turns out the pitch I was hearing was two septimal whole tones below the tonic.
But there it was. . .
I was fortunate to have spent the last month on the road opening the show for the
Allman Brothers Band. I told that story to Derek Trucks, and he threw back his head
and laughed " The Hate Note!". . .
Derek obviously has his own terminology, but yeah, there's a note there @ 738 cents
or so that is clearly part of the blues vocabulary. And no, it's not pretty. . .

I think Lalaland mentioned the use of the 7th partial in North Indian Classical music.
I think not. . .
An old friend of mine, Ken Zuckerman, who is the director of the Ali Akbar College of
Music in Basel, Switzerland on a recent trip to the states told me of the admonishment
he recieved from Ali Akbar on his intonation around the flat 7th.
Our cultural preconditioning in America from our exposure to Blues/Jazz/Gospel etc.
allows us to hear that area much flatter than the North Indian music allows.
Komal ni is almost a quarter tone above the 7th partial. I like 'em both. . .

Anyway, the basic idea that I'm working with here is that 12 edo is a piano tuning, and
I'm a guitarist. . .
So I just work with the sounds I like, and use the 12 edo grid as a jumping off point for
whatever adjustments I can manage.
I guess you could call it "Adaptive Just Intonation", or "tune on the fly", but whatever
you call it, it's how everybody that plays a variable pitch instrument plays, so I'm doing
my best to understand it.
It's really got very little to do with math.
It's just about observing the vibrating string and singing with a drone.

Play/sing first, measure later if it doesn't make sense.
I'll be out of town for a couple of days, back at the computer tuesday, maybe.
I got nothing but respect for anybody who's working in this area, it's a little lonely
off the grid. . ."
Here's a little more from Kimock and Jamie

Originally Posted by lalaland View Post
Yea, I'm aware of the fifths overshooting the octave, by 24 cents I think. If you're creating modes using both fifths and thirds...

Say major scale: (Speaking vs a 12EDO)
Root, tonic at 0 cents.
Second, two fifths up, 4 cents sharp.
Third, using a third up, 22 cents flat.
Fourth, fifth down, 2 cents flat.
Fifth, fifth up, 2 cents sharp.
Sixth, third of a fifth down, 20 cents flat.
Seventh, third of a fifth up, 20 cents flat.

The cent values are all approximate.

The sixth is really throwing me off. Hum. Someone want to chime in and let me know?

Originally Posted by kimock View Post
The 5-limit offsets are incorrect, they should all be in that 14 to 16 cent range.
Sixth? You got the path right, you got the math wrong, is that why it's bothering you?
Dha is about 16 cents flat of the fret.
The 3rd above the 4th (the fifth below)
Or, 5th below the 3rd (same diff)

The sixth is a difficult interval for me as well, I'm sure I know exactly where it's at until I try to sing it in tune. Ouch. . .really really bad!!!

Oh my god. Like, seriously, I'm sitting in class reviewing for finals, sin, cosin etc. and I can't even add. I swear, I will be so happy to be out.

Of course, as always, you're correct. 386 cents = 14 cents flat. Somehow in my mind I was thinking 388 and coming up with 22.

Lets try that again!

Root - 0 cents
Second - two fifths up, (204) 4 cents sharp.
Third, third up, (386) 14 cents flat.
Fourth, fifth down, (498) 2 cents flat.
Fifth, fifth up, (702) 2 cents sharp.
Sixth, third of a fifth down, (884) 16 cents flat.
Seventh, third of a fifth up, (1088) 16 cents flat.

Last edited by Clifford D at Dec 2, 2007,
The standard guitar only has one single interval on it that is truly in-tune, that is the octave. ALL other intervals have been mistuned, or 'tempered', to be out of tune.
The best way to play in-tune is to get a guitar with Harmonic Series frets, these are available from FreeNote Music. When you use these pitches, you can play a 7th or 11th or 13th chord with a ton of distortion, and it will sound right, because the overtones of the distortion will not be conflicting with the fretted notes.
Here's some modern jazz/rock in Harmonic Series tuning: www.fretlessbrothers.com
And a link to the guitars: www.microtones.com