Guitar: This is a dilly.

Subject: RE: Guitar: This is a dilly.
From: GUEST,midwestern Irish gal
Date: 27 Jan 06 - 02:02 AM

That same phenomena has happened with at least 3 instruments, one was a 12 string which I used to tune to some DADGUM tuning(it's been so many years I can't remember which one), but at least one whole step below concert pitch, then down from there. Everytime I tried to touch the harmonics it sounded way sharp.
Then there's this funky 17 stringed not-exactly-an-oud-or-lute-whatchamacallit I got years ago from an Oud maker in Northern Turkey where they still play quarter tone music. The tuning is really funky & the harmonics always go wildly sharp. I once had the gauge of the steel strings measured by a guitar repairman pal so I could replace them. No doubt that exchanging original strings with different ones made it more pronounced, as the strings have always seemed loose.
    And, I have a Neapolitan Mandolin (rounded back with 33 ribs) which has a remarkable voice, but if I pluck one course of strings, the sound goes dramatically sharp as it sustains & fades.
    What I want to know is, why do some instruments have strings that go sharp & I have to lower the pitch to get them in tune, and some instruments are the opposite?

Subject: RE: Guitar: This is a dilly.
From: GUEST,Anonny Mouse
Date: 26 Jan 06 - 03:50 PM

Don't think its a "Doppler effect" as that is associated with moving things (like trains or cars and their horns). Could be due to some physics of decay with harmonics...I do these on my git too, but haven't noticed a perceived rise in pitch. May be a brain-thing too. But I'll be paying attention to it a bit more anyway.

Subject: RE: Guitar: This is a dilly.
From: Peace
Date: 26 Jan 06 - 11:52 AM

Thank you all very much for your thoughts, energy and answers. It's certainly a strange phenomenon.

"My sister once said something similar, but added "all he needs now is a personality." She reminds me occasionally."

John, I think you are one of the nicest, most interesting people around this place. Kind, brilliant and witty. Man, it don't really get no better than that.

Subject: RE: Guitar: This is a dilly.
From: DADGBE
Date: 21 Jan 06 - 09:37 PM

It's fun to play around with this although I have no idea of why it should happen. My Martin does the same thing and it gets more obvious as the strings get further and further below normal tension. Eventually, of course, they get so slack that there ain't no more tone a'tall.

Subject: RE: Guitar: This is a dilly.
From: Peace
Date: 21 Jan 06 - 12:33 PM

I will compose a proper reply in a bit. I'm dickin' with the guitar now and reading posts to put what I read into 'action' and like that. The ideas and explanations here are brilliant. I don't know if y'all are aware how darned smart you are. If you aren't ya should be.

Subject: RE: Guitar: This is a dilly.
From: Jeri
Date: 21 Jan 06 - 12:27 PM

"Doppler would not account for the shift from an unmoving source"

You're wrong about that being universally true, but in this case, that's what I was saying. Not obviously though. What I said Doppler was "how we perceive wave length due to direction of movement and speed."   Quibble, quibble.

Subject: RE: Guitar: This is a dilly.
From: Once Famous
Date: 21 Jan 06 - 12:24 PM

Of course, this is the effect of a well made and well played Martin guitar, where like a fine and aged cooking utinsil, it is part of the recipe for quality in it's output.

I get a similiar harmonic on my well-played 35 year old D-18.

Subject: RE: Guitar: This is a dilly.
From: gnu
Date: 21 Jan 06 - 12:10 PM

I find Peace's music has a rather moving effect.

Okay... I'll leave without being told.

Subject: RE: Guitar: This is a dilly.
From: Amos
Date: 21 Jan 06 - 11:26 AM

Doppler would not account for the shift from an unmoving source; the waves might be slightly compressed and expanded by the ebb and flow of contraction in the guitar, but I think that would be very small as an effect. I think the rise is due to cross-interference in harmonics, pretty much what John described; even a very closely tuned instrument has some of this.

A

Subject: RE: Guitar: This is a dilly.
From: Jeri
Date: 21 Jan 06 - 11:17 AM

Doppler effect, and light does it too. Sound gets lower when moving away because the waves appear to lengthen and it gets higher as sound waves approach because they appear to shorten. Light ges redder or bluer for the same reasons - how we perceive wave length due to direction of movement and speed.

Subject: RE: Guitar: This is a dilly.
From: Once Famous
Date: 21 Jan 06 - 11:08 AM

Sound plays tricks when it is moving through the air. A train whistle or horn sounds quite different when it is in front of you and then moving away from you.

Subject: RE: Guitar: This is a dilly.
From: Jeri
Date: 21 Jan 06 - 10:57 AM

I said your answer was virtually crap-free. Do I get a mention?
Seriously, I appreciate having you and your brain around.

Subject: RE: Guitar: This is a dilly.
From: JohnInKansas
Date: 21 Jan 06 - 10:55 AM

Amos -

I shall add your fine compliment to my list and to my resumé.

(If my list gets any longer, I may have to go to a 4x6 inch index card.)

My sister once said something similar, but added "all he needs now is a personality." She reminds me occasionally.

John

Subject: RE: Guitar: This is a dilly.
From: gnu
Date: 21 Jan 06 - 10:42 AM

Snarky... guitar licks? Ditto what A said, John.

Subject: RE: Guitar: This is a dilly.
From: Jeri
Date: 21 Jan 06 - 10:31 AM

Following is an answer which, unlike what JinK has presented, may be 99% crap.

Lower tension strings sound lower than higher tension strings
Tension is determined by string length vs length of the thing it's held by. In a guitar, that's usually the tuning peg and bridge pin.
When you tighten the tuning peg, you shorten the string.

How you might raise the pitch of the string and therefore, the harmonic, would be to shorten the string or lengthen the space it's stretched along.

Now, for the harebrained (and low tech) theories:

When a guitar string is vibrating a lot, it pulls the neck in and/or the guitar face and shortens the length the string is stretched thereby reducing tension. When the vibrations subside, the wood parts go back to normal and the pitch rises.

The string itself may stretch out when it vibrates a lot and become looser and lower in pitch, then get highter when the vibrations subside and it goes back to resting length.

Anybody who uses an electronic tuner on a violin likely has found what I have: 1) If a plucked string is in tune, a bowed one likely isn't, and 2) You change the pitch of a sting by how hard you bow. The funny thing is, some strings get flatter and some sharper with harder bowing. That may be caused by the more obvious stretch of the string/wood/ by the force of the bow itself.

Subject: RE: Guitar: This is a dilly.
From: snarky
Date: 21 Jan 06 - 10:18 AM

lick lick

Subject: RE: Guitar: This is a dilly.
From: Amos
Date: 21 Jan 06 - 09:59 AM

John,

I am, yet again, awed by your technical insight and expository talent.

A

Subject: RE: Guitar: This is a dilly.
From: JohnInKansas
Date: 21 Jan 06 - 02:46 AM

It's not an unknown or surprising effect, but it gets really complex to make any very specific SWAGs about exactly what's going on in any particular case.

When you pluck a string, you have to pull is sideways a bit, so the tension is slightly increased (hopefully the weight/mass of the string stays constant). This means any plucked note "starts sharp" and as the amplitude of the vibration decreases, the pitch drops. Long arguments can ensue between those who tune to the "attack" pitch and those who tune to the "fadeout" pitch.

When you pluck anywhere except dead center on the string (and sometimes even there) the string will have some "harmonics" in how it vibrates. Each "harmonic mode" acts a bit like a separate little string, that's connected to the other harmonics' separate little strings, so energy can feed back and forth between the individual "harmonic modes." This sometimes leads to audible "beats" that can be heard, and that in fact can be used for tuning. Transfer of energy between individual harmonics of the motion will change the "harmonic content" of the tone as the string motion decays.

The "acoustic impedance" at the bridge and nut, where energy is transfered from the string to the guitar body (to make the noise) varies with frequency, so different of those little "string modes" will transfer a different fraction of the "mode energy" to the guitar body each time a wave slaps the bridge. This, and that the "harmonic modes" are also "trading energy" with each other, also causes the harmonic content of the vibration to change as the string amplitude fades.

So when something changes while the note rings out, it's not surprising.

But if you want the real technical explanations, you'll need to read several very large and boring textbooks, apply a bit of expensive test equipment - and the answer will only apply to the one guitar for which you do the work, (and probably will change when the strings get dirty).

In this particular case, when you strum at the 12th fret, the string frequencies will be at what's "natural" for the place where you fretted. When you release the neck, the frequency content may be out of tune with the octave of the open string, so the existing harmonics will try to pass their energy to slightly different harmonics that fit the open string lenght, which will change the apparent pitch as the energy is transferred to "more efficient" modes of vibration.

Translation of last paragraph: Your 12th fret probably isn't exactly in perfectly compensated position and you're guitar is out of tune - if you're hearing a strong effect.

Advice: It sounds like a neat effect. Work it into your music.

John

Subject: RE: Folklore: This is a dilly.
From: Bee-dubya-ell
Date: 21 Jan 06 - 02:09 AM

Peace, your guitar is suffering from a malady common to older Martins that have spent most of their lives in colder climates, like Canada. It needs an extended period of convalescence in a much warmer place, like Florida. A rest period of, say, five to ten years is usually adequate.

I would be willing to provide convalescent services, including a physical therapy regimen with frequent vigorous workouts, for a nominal fee. Oh, heck! You're a nice guy, so I'll do it for free!

Subject: RE: Folklore: This is a dilly.
From: Amos
Date: 21 Jan 06 - 01:00 AM

Good test, Bugsy!! Interesting effect. So much for blaming Peace's ear!! :>)

A

Subject: RE: Folklore: This is a dilly.
From: Peace
Date: 21 Jan 06 - 12:58 AM

Good thought, Amos. I can hear it happening but can't figure out why.

Subject: RE: Folklore: This is a dilly.
From: Peace
Date: 21 Jan 06 - 12:57 AM

Thank you very much, Bugsy. Lets me know that I ain't completely losin' it.

Subject: RE: Folklore: This is a dilly.
From: Amos
Date: 21 Jan 06 - 12:57 AM

It's kinda counter-intuitive to think it would increaser in frequency as the energy is dissipating. What is more likely is that the mix of harmonics is changing and your ear is picking up the higher ones as the lower ones fade. That's just a wild-ass guess, though. Could be the old Martin is stiffening up at the last minute, I guess!!


A

Subject: RE: Folklore: This is a dilly.
From: Bugsy
Date: 21 Jan 06 - 12:55 AM

I just tuned my Maton the to the sam tuning as yours and tried the harmonic on 12 fret. I also put my Intellitouch tuner on the headstock to check. Th note seamed to oscillate between Sharp and Flat then finish slightly sharp.

It wasn't obvious to my "Wooden Ear" though.

Cheers


Bugsy

Subject: RE: Folklore: This is a dilly.
From: Peace
Date: 20 Jan 06 - 11:14 PM

LOL

I bloody knew this thread would not be taken seriously. But it's a serious question. (I guess that would explain why the neck seems so rigid and the action so stiff, huh?"

Subject: RE: Folklore: This is a dilly.
From: GUEST,Art Thieme
Date: 20 Jan 06 - 11:11 PM

It ought to be obvious.

You were handling Viagra before picking up the guitar!

Art

Subject: RE: Folklore: This is a dilly.
From: Peace
Date: 20 Jan 06 - 11:08 PM

LOL

Subject: RE: Folklore: This is a dilly.
From: GUEST
Date: 20 Jan 06 - 10:46 PM

Silly Twit - of course it is rising from D to G

Subject: RE: Folklore: This is a dilly.
From: Peace
Date: 20 Jan 06 - 10:12 PM

PS I didn't know whether to put this under folklore of tech. If I have made a mistake, please excuse me and place the thread as is appropriate. I promise not to mention the "c" word.

Subject: Folklore: This is a dilly.
From: Peace
Date: 20 Jan 06 - 10:11 PM

Here's the scenario, and I don't know what the answer is or why.

I have my old Martin in an open tuning (open D) and it is tuned two and a half full tones below concert. OK?

Now, when I finish the chord at the end of the particular song I'm working on, I hit the harmonics at fret twelve. That's when this really strange thing occurs. I take my hands off the neck of the guitar and just let the last chord (harmonic) fade. It seems that as it fades, it begins to rise a bit in key. Does anyone have a reason this would happen?