Bow pressure changing string pitch

[Bill Yacey]

I have noticed when using gut or perlon wound strings that some strings are more pitch sensitive to bow pressure and position of the bow hair on the string. The truest tone and pitch seem to occur when bowed closer to the bridge.

Is this a normal side effect of using low tension strings (compared to steel)? Steel strings don't seem to exhibit this effect. Is it perhaps out of phase reflections back through the bridge that are creating this detuning from the natural pitch of the string?

[martin swan]

I've only really noticed it on the G string - I assume that if the string's a bit stretchy and you push down on it you're making it longer and therefore detuning it.Steel strings just don't stretch as much ....

But I'm no scientist, it's probably something completely different!

[Bill Yacey]

Initially I thought it was something like that, but even though applying more pressure lengthens the string slightly, you are also raising the tension by applying more pressure. Albeit, it's a miniscule amount using normal bow pressures, I find it's still enough of an audible change to be an annoyance; the pitch can go up or down by as much as 20 cents. I noticed also that a down bow may produce one pitch and an upbow changes the pitch again.

[La Folia]

I'm astonished that you find that steel strings don't do that. They are incredibly nonstretchy, which is why you have to use a fine tuner. Any tiny change in the length of the string makes a big change in tension, and that's why the pitch goes up with amplitude. Gut and synthetic strings are MUCH less sensitive to this problem than wire steel strings. Wound strings should also be more sensitive to the problem than unwound strings or wire strings.

If you've ever played a tiny child's violin with wire steel strings, it makes a great demonstration. Synthetics work a whole lot better on those violins. (Although steel is used more often, mainly because if you have to tune 30 tiny violins, you don't want to mess with 120 awful pegs.)

Gut and synthetic G strings show a little of that if you're listening for it. Perhaps you're comparing them to wound steel strings. (I don't know how those compare--never tried them.) Maybe light strings are worse than heavy strings(?), but I guess the idea of light strings is that you're not going to be digging into them anyway(?).

[Bill Yacey]

The strange thing I have found is that the initial note upon attack is flat from the natural tuning of the open string, and then you have to either lighten up pressure or move the placement of the hair on the string before it'll start sounding at the correct pitch. I first I thought it's just something quirky about a particular instrument, but I've noticed this on various instruments. I know excessive pressure will cause a string to sound unnaturally flat, but I'm talking about ordinary bow pressure well within what's acceptable for playing.

[Carl Stross]

Initially I thought it was something like that, but even though applying more pressure lengthens the string slightly, you are also raising the tension by applying more pressure. Albeit, it's a miniscule amount using normal bow pressures, I find it's still enough of an audible change to be an annoyance; the pitch can go up or down by as much as 20 cents. I noticed also that a down bow may produce one pitch and an upbow changes the pitch again.

Bill, I think you are an electronics engineer. It's exactly what's happen when an osc is too tightly coupled to the next stage. The bow adds weight to the string, the fartehr from the bridge , the more.

[martin swan]

I'm afraid I've only noticed this with poor quality strings .... or at least, it's a reason I don't use some brands of string!

Carl's explanation makes sense, but please go into a bit more detail - for instance, why are some strings susceptible and not others? I assume the difference in ptich between up and down bow is due to the position shifting relative to the bridge, but maybe not?

[Carl Stross]

I'm afraid I've only noticed this with poor quality strings .... or at least, it's a reason I don't use some brands of string!

Carl's explanation makes sense, but please go into a bit more detail - for instance, why are some strings susceptible and not others? I assume the difference in ptich between up and down bow is due to the position shifting relative to the bridge, but maybe not?

Martin, I'd expect all strings to do that to some extend but I can't come up with why some do it more and some less. I'll think about it.

[La Folia]

I know excessive pressure will cause a string to sound unnaturally flat, but I'm talking about ordinary bow pressure well within what's acceptable for playing.

Flat you say? I suppose it's possible you are observing some sort of anomalous coupling, but it usually goes sharp, not flat, with excessive pressure.

[Bill Yacey]

In examining this I was careful not to change the position of the hair on the string between an up bow or down bow, and I made every effort to maintain the same bow pressure, to eliminate this variable.

Maybe the bridge / corpus coupling does have some sort of loading effect on the string oscillations, although I wouldn't consider the string oscillations as a high impedance source susceptible to loading, like a free running electronic oscillator. Whatever this is that's occuring, it's probably directly responsible to the responsive quality of the instrument to initial bow attack.

It is primarily the wound strings that I've experienced this on, D and G being the worst offenders. For years I've used Thomastik Super Flexible steel strings, and they seem to play fairly true compared to my experience with Dominants or gut. Has anyone here experience with the new line of Infeld strings?

[martin swan]

Well it's a common phenomenon, and always flat not sharp.

Maybe the pressure on the string is pulling the bridge over a bit? But then you'd expect it to happen with any type of string ......

MYSTERY

[Bill Yacey]

Flat you say? I suppose it's possible you are observing some sort of anomalous coupling, but it usually goes sharp, not flat, with excessive pressure.

This is why I'm beginning to think that it's some sort of non-linear interaction between the hair and the moving string.

[Carl Stross]

This is why I'm beginning to think that it's some sort of non-linear interaction between the hair and the moving string.

Happens when you pizz as well. It's not an ideal string.

[La Folia]

Well it's a common phenomenon, and always flat not sharp.

That's a different phenomenon, one that I have never observed.temp.mp3

[Craig Tucker]

The truest tone and pitch seem to occur when bowed closer to the bridge.

Where bow pressure has much less of an effect on string length?

I believe that other than with regard to playing open strings, where the problem is bow only, minute changes in bowing pressure and/or finger position, are the easiest way to compensate for this type of intonation problem...

[Bill Yacey]

I've moved the post further south from the bridge, about 8 mm now; it seems to have improved considerably.

[Bill Yacey]

Where bow pressure has much less of an effect on string length?

I believe that other than with regard to playing open strings, where the problem is bow only, minute changes in bowing pressure and/or finger position, are the easiest way to compensate for this type of intonation problem...

If the instrument is that sensitive to bow pressure, playing it would be akin to balancing on a high wire at the circus. There has to be an acceptable window of bow pressure in able to anticipate what pitch is going to be sounded.

I'll see if I can record a sample of this later when I get to the studio.

[Addie]

One of the recent papers on bowing talked about this at length, with diagrams, real data, etc. (real data!!! ). Something about the limitations of bowing force due to change of pitch.

Could it have been the Scoonerwaldt dissertation? Couldn't cough it up again in a hurry, sorry.

[Bill Yacey]

I understand the practical limitations of bow pressure, but what I was experiencing is with pressure of little more than the weight of the bow itself, or with slight pressure applied, well within practical playing limits.

[La Folia]

Er, Bill, I'm genuinely curious about this, but I have no idea what you're talking about. Can you post your own brief sound file and see how it compares to mine?

[Bill Yacey]

I'll record one and post it later.

[La Folia]

Thanks.

[Bill Yacey]

I decided I'm not going to the studio, it's - 25C here right now, so I'll be staying in. I made a recording with a crappy computer electret; here it is.

Warble.mp3

[La Folia]

Wow, that's definitely something else, isn't it? The sound is breaking, kind of like a wolf.

[Bill Yacey]

It's something alright. I sure wish I knew what causes this.