CAPO,,in tune out tune..

willem
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Sun Dec 19, 2010 3:29 am

I read something in Reivers upload ''mad world'',,it's about capo the guitar and be out of tune,,i thought it would be nice to put here your knowledge and more about capo's etc..


wrench
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Sun Dec 19, 2010 10:49 am

Willem, my friend, you know how to coax me out of my shell by discussing the physics of guitar.

Capo was frustrating to study because before one starts to study, he knows you need to re-tune after placing the capo on the neck, and after completing study, one still knows he must re-tune the guitar after placing the capo on the neck. No matter how much you study, you will not change the outcome.

The frets are spaced on the neck to equal a portion of the remaining string length at an interval such that each fret is approximately a half-step. That is why the fret spacing decreases as they go up the neck. That portion is not exact, and as you go further up the neck, the error is achieved in a shorter distance, just as the frets get closer together. The actual amount of the accumulating error is very small, however, and does not result in most of the error. The largest part of the error comes from the string. The string holds most of the variables that make up the sound you hear from it. Length, mass, tension, stiffness, material, action height, intonation, fingering distance from the fret, and a few other things are all variables that will affect how any particular fretted note turns out. Most of these string variables most players don't know or control, and other variables are built into the guitar, so the player still can't know or control all the variables. For example, I'm certain it is a very small number of us who have mapped the location of our frets with a Coordinate Measuring inspection device. And even if you did, you still need to re-tune after placing the capo.

Here are a few things I found out:
1. Placing the capo anywhere on the neck causes a tuning error
2. The error is always sharp
3. Strings of higher mass have greater error
4. The b string has the highest error if the saddle has b string compensation
5. The G and e strings have the lowest error - nearly zero
6. Dirty wound strings have higher error because they have higher mass from the dirt
7. The guitar sounds out of tune with a capo installed because all the strings are sharp by a different amount
8. A perfectly intonated guitar with new strings was 25 cents was sharp at b, 20 cents sharp at E, 18 cents at A, 15 cents at D, and 0 at G and e
9. A larger E string with the same core diameter was still 20 cents sharp
10. A larger gauge E string with a larger core diameter was 25 cents sharp
11. Longer scale lengths have smaller error

I took tuning measurements with a Korg TU-40 tuner and a Korg CM-100L piezoelectric contact microphone attached to the headstock so the guitar's body acoustics would not interfere with readings.

An interesting observation I made is the role of sympathy notes in affecting the pitch ultimately produced. Specifically, with a capo at the 12th fret, and the E string measuring 20 cents sharp while the b string measured 25 cents sharp, I plucked them at the same time. The resulting note was an E in perfect pitch - no error. I understand the resulting note being E because the frequency of b is exactly 3 times that of E, but I don't yet understand why it was in perfect pitch. I may repeat this and feed the signal into Audacity to analyze the result. That reminds me of a certain guitar I got that had a weird characteristic that fretting the first string at the 7th fret resulted in the b note as expected, but if the note was simultaneously plucked with an open E, the b rang an octave higher as if it were fretted at 19. I scratched my head about that until I changed strings the first time, after which this has never happened again.

Man, I need a job. I obviously have WAY too much time on my hands!


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neverfoundthetime
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Sun Dec 19, 2010 11:10 am

... er who needs my blurb when we have Dan around!
Willem.... what the man said! :)


Chasplaya
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Sun Dec 19, 2010 12:11 pm

Great article Dan, out of all that I learnt I need to clean and change strings more often cos not much else you can do really , unless you get one of those squiggly fretted guitars lol!

Image

Dan you are a bit like me researching when we should be playing lol!


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TGNeil
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Sun Dec 19, 2010 12:48 pm

Dan-

We must have been typing at the same time as you took the words right out of my mouth! I was just in delay mode waiting for spellcheck, grammercheck and sciencecheck to kick in. I love stuff like that and always have to be careful with how much to tell somebody who asked that type of question You're explanation was great and thanks for these types of contributions.

Neil


willem
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Sun Dec 19, 2010 1:26 pm

I'm glad my headstock tuner is chromatic...


BigBear
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Sun Dec 19, 2010 1:39 pm

wrench wrote:
Willem, my friend, you know how to coax me out of my shell by discussing the physics of guitar.

Capo was frustrating to study because before one starts to study, he knows you need to re-tune after placing the capo on the neck, and after completing study, one still knows he must re-tune the guitar after placing the capo on the neck. No matter how much you study, you will not change the outcome.

The frets are spaced on the neck to equal a portion of the remaining string length at an interval such that each fret is approximately a half-step. That is why the fret spacing decreases as they go up the neck. That portion is not exact, and as you go further up the neck, the error is achieved in a shorter distance, just as the frets get closer together. The actual amount of the accumulating error is very small, however, and does not result in most of the error. The largest part of the error comes from the string. The string holds most of the variables that make up the sound you hear from it. Length, mass, tension, stiffness, material, action height, intonation, fingering distance from the fret, and a few other things are all variables that will affect how any particular fretted note turns out. Most of these string variables most players don't know or control, and other variables are built into the guitar, so the player still can't know or control all the variables. For example, I'm certain it is a very small number of us who have mapped the location of our frets with a Coordinate Measuring inspection device. And even if you did, you still need to re-tune after placing the capo.

Here are a few things I found out:
1. Placing the capo anywhere on the neck causes a tuning error
2. The error is always sharp
3. Strings of higher mass have greater error
4. The b string has the highest error if the saddle has b string compensation
5. The G and e strings have the lowest error - nearly zero
6. Dirty wound strings have higher error because they have higher mass from the dirt
7. The guitar sounds out of tune with a capo installed because all the strings are sharp by a different amount
8. A perfectly intonated guitar with new strings was 25 cents was sharp at b, 20 cents sharp at E, 18 cents at A, 15 cents at D, and 0 at G and e
9. A larger E string with the same core diameter was still 20 cents sharp
10. A larger gauge E string with a larger core diameter was 25 cents sharp
11. Longer scale lengths have smaller error

I took tuning measurements with a Korg TU-40 tuner and a Korg CM-100L piezoelectric contact microphone attached to the headstock so the guitar's body acoustics would not interfere with readings.

An interesting observation I made is the role of sympathy notes in affecting the pitch ultimately produced. Specifically, with a capo at the 12th fret, and the E string measuring 20 cents sharp while the b string measured 25 cents sharp, I plucked them at the same time. The resulting note was an E in perfect pitch - no error. I understand the resulting note being E because the frequency of b is exactly 3 times that of E, but I don't yet understand why it was in perfect pitch. I may repeat this and feed the signal into Audacity to analyze the result. That reminds me of a certain guitar I got that had a weird characteristic that fretting the first string at the 7th fret resulted in the b note as expected, but if the note was simultaneously plucked with an open E, the b rang an octave higher as if it were fretted at 19. I scratched my head about that until I changed strings the first time, after which this has never happened again.

Man, I need a job. I obviously have WAY too much time on my hands!

Holy smoke Dan!! I'm afraid to ask you what time it is for fear of getting complete instructions on how to build the watch!! LOL!

Excellent dissertation!! Silly me, all this time I thought the problem with capos was the pressure of the capo exerted downpressure on the strings using the fret as a fulcrum, thus increasing string tension and causing the strings to go sharp.

My best advice is place the capo as close to the fret as possible (thus shortening the lever) and re-tune as needed.

Thanks Dan! :cheer:


sws626
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Sun Dec 19, 2010 4:20 pm

Hi Dan,

This is an excellent study and completely in line with my accidental experience -- based on which, I always retune after applying the capo and usually end up changing strings more often if I'm using a capo frequently.

Did you happen to notice whether placing the capo closer or further from the fret made any appreciable difference? Or whether a guitar capoed on, say fret 5, and retuned suffered any intonation issues higher on the neck?

-Stuart


millponddave
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Sun Dec 19, 2010 5:13 pm

OK, that brings up more questions.

1) Do you retune to the note of the string that the capo is on ?

2) Doesn't the capo keep the string from moving?

Dave


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neverfoundthetime
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Sun Dec 19, 2010 5:37 pm

I just played all day Saturday with Marc and I had a capo on fret 1 (12 strings) all the time as my guitar is tuned down a half step. I was re-tuning quite often and at the end of the day my strings looked shot. So the capo use certainly wears out the strings quicker but usually you only capo for one song and take it off. Obviously, a day of capo on was not kind to my strings.

Dave, the capo doesn't stop you tuning the string... its only a slight adjustment you are making. You don't retune to anything, you capo up (in my case one fret) so all the strings should be a note higher and just slightly adjust if slightly out.


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