Out of tune

[Willie Poole]

Every time I ever seen Monroe need to tune his mandolin he gave it to his guitar player to do it, one of his band members told me that Bill didn`t have a good enough ear to tune on the fly, that was well before we had electronic tuners in every case....Buzz used to stick his mandolin right up into the mike so he could really hear it through the speakers, again that was before electronic tuners were popular...

Willie

[Franc Homier Lieu]

My own mandolin even slightly out of tune drives me crazy. Yet this is truly music to my ears. Go figure.

[foldedpath]

I suppose in some alternate universe where I only played alone at home, then maybe I could get interested in this idea of a wet-tuned mandolin. Although I've tried so hard to be in tune for so many years, that it would take some convincing.

In my real world though, I play with other musicians using instruments that are already slightly at odds with 12TET pitch, like fiddlers with strings tuned in perfect 5ths, and diatonic instruments with their own scale quirks like whistles and flutes, and pipers where the drones may or may not be in their own "wet" relationship to the chanter. Somehow it all works when playing unison melody together in an Irish/Scottish trad session. The mix of instruments creates its own slightly swirling dissonance that still sounds good to the ear.

But with all that variability in pitch around me, or even when just playing at home with my fiddler S.O., the last thing I want is even more pitch variation from my own instrument. If I'm locked into 12 Tone Equal Temperament with my mandolin's frets, then I want to at least be *in* that tuning, and I'll live with the consequences. So I get it as close as I can to perfect unison on the strings. Anything else would drive me nuts.

[Bob A]

I've noted the ceiling fan issue as well.

illie's comment about the fiddler playing a bit flat for notice reminded me of violinists and vocalists who play/sing just a bit sharp, for the same object of being noticed above the crowd.

[catmandu2]

This is a vast an interesting topic to me from an anthropological view - relative aesthetic conceptions of consonance/dissonance.

Around the world exist so many alternatives to 12tet. My own appreciation began with Coltrane, Miles' electric ensembles, burgeoning interest in trad forms, early music, et al.

12tet enables increasingly larger ensemble. Trad and folk forms typically entail solo and small ensemble providing quite a bit more latitude to exploit extended tonal palette. One reason I enjoy wire harp, for example, is the pervasive overtones that can be mixed for great tonal complexity.

[Cochiti Don]

I suppose in some alternate universe where I only played alone at home, then maybe I could get interested in this idea of a wet-tuned mandolin. Although I've tried so hard to be in tune for so many years, that it would take some convincing.

In my real world though, I play with other musicians using instruments that are already slightly at odds with 12TET pitch, like fiddlers with strings tuned in perfect 5ths, and diatonic instruments with their own scale quirks like whistles and flutes, and pipers where the drones may or may not be in their own "wet" relationship to the chanter. Somehow it all works when playing unison melody together in an Irish/Scottish trad session. The mix of instruments creates its own slightly swirling dissonance that still sounds good to the ear.

But with all that variability in pitch around me, or even when just playing at home with my fiddler S.O., the last thing I want is even more pitch variation from my own instrument. If I'm locked into 12 Tone Equal Temperament with my mandolin's frets, then I want to at least be *in* that tuning, and I'll live with the consequences. So I get it as close as I can to perfect unison on the strings. Anything else would drive me nuts.

You lost me with 12 tone equal temperament. I'm just too much of a beginner

[Cochiti Don]

I think that's what bothered me about the rock band "Boston " They were just so annoyingly in perfect harmony.

[Bertram Henze]

You lost me with 12 tone equal temperament. I'm just too much of a beginner

That's easy. Most of it is just math.

[Teak]

These frequency beats are something us mandolin players are more aware of than other instrumentalist because of the "twined" strings. Years ago, when ceiling fans in homes was becoming popular, I was at a jam in a picker's home, standing right under his new ceiling fan. I could not get my mandolin in tune try as I might. Dad who had as good of ear as I've ever known said I sounded fine but I couldn't get rid of those d##m beats. When I moved from under the fan I was in tune.

I wonder if the ceiling fan issue was due to the Doppler shift. Seriously. When your mandolin's sound waves hit the fan blades they were reflected back to you at a slightly lower or higher frequency. This is similar to an ambulance or police siren sounding higher pitched as it approaches you versus going away from you. I suspect being right under the fan caused your sound waves to bounce directly back to you versus being away from the fan would cause a reflection in a different direction. As kids we used to talk into fans to hear how our voices were changed in pitch.

[David L]

I wonder if the ceiling fan issue was due to the Doppler shift. Seriously. When your mandolin's sound waves hit the fan blades they were reflected back to you at a slightly lower or higher frequency. This is similar to an ambulance or police siren sounding higher pitched as it approaches you versus going away from you. I suspect being right under the fan caused your sound waves to bounce directly back to you versus being away from the fan would cause a reflection in a different direction. As kids we used to talk into fans to hear how our voices were changed in pitch.

The ceiling fan would reflect the sound at different times and directions, but not different speeds, so there would be no Dopler effect. There would be differences in volume, but not pitch. Sometimes it is difficult to tell the difference. The fans in the resonator tubes of a vibraphone change the volume (tremolo), but many people perceive it as a change in pitch (vibrato).

[Bertram Henze]

I wonder if the ceiling fan issue was due to the Doppler shift.

Let's be realistic: of course, there is a Doppler shift in the reflection from moving objects (simple explanation here), BUT...

- to be audible, the area of the moving object must be considerably large, compared to the other static objects around you (how big is your fan anyway?)
- directly under the fan, there is always as much percentage of effective area moving towards you as is moving away from you, so even if audible, the effect can only spread out the pitch in both directions.

[sblock]

The ceiling fan would reflect the sound at different times and directions, but not different speeds, so there would be no Dopler effect. There would be differences in volume, but not pitch. Sometimes it is difficult to tell the difference. The fans in the resonator tubes of a vibraphone change the volume (tremolo), but many people perceive it as a change in pitch (vibrato).

Strictly speaking, the physics in your response is not correct. Yes, there will be a Doppler effect. The sound that reflects off a moving surface that is advancing directly towards the source with velocity, v, will return Doppler-shifted in frequency, approximately according to:

[change in frequency of the reflected sound] = [frequency at the source]*(v/c),

where c is the speed of sound in air (about 300 m/s).

For the tip of a fan blade moving at, say, about 2 m/s, the maximal change in the reflected frequency is therefore about 2 parts in 300, or 0.6%. A note of A440 Hz will change by +3 Hz to A443 Hz, which can be heard as a different pitch!

Of course, the geometry of the reflected sound from a fan is rather complex. Off to the side of the fan, and some portions of the blades are moving towards you, while some are moving away. Stand directly in front, and the blades immediately across are spinning, but mostly not moving towards or away from you, to any real extent. However, the edges of the fan still have a some directional components towards and away from you -- and give a Doppler shift. The effect is strongest off to the side of the fan, and not in front, but it happens at all angles.

In summary, a fan generates a complex return of sound that IS, most definitely, Doppler-shifted -- but both up and down in frequency -- and so it spreads out the source sound spectrum somewhat. This is not a modulation in intensity. It is a modulation in the pitch.

As to whether a conventional ceiling fan reflects enough sound to make much of a difference to a player seated in a small room, I couldn't say. It would depend very much upon the size and speed of the fan, and the audio sensitivity of the player. I'm inclined to suspect the effect would be pretty minimal, and besides, the reflected noise (even if freq-shifted) is small compared to the direct sound from my instrument. I suppose one could try to measure it, but (anecdotally) I have never noticed any tuning differences in the rooms I've played with ceiling fans, which are usually rotating fairly slowly (< 0.5 m/s). But then again, I don't suffer from the curse of "Golden Ears."

On to a different topic:

Also, the fans used in a vibraphone resonator are not really fans (although they're called this): their blades have no pitch! And your explanation is, unfortunately, therefore a bit off. These flat "fan" blades are simply there so that they alternately open and occlude the resonator openings at a fixed frequency (given by their rotation speed x number of blades). When the vibraphone resonators are partially blocked by the flat blades, their dominant resonant frequency (this is the so-called "organ pipe" frequency) is lowered, reducing the frequency of the note that's emitted by just a bit. The steady fan rotation leads to a fast, alternating opening-closure of the pipe, and thereby causes the pitch to waver, introducing a vibrato effect. And this has nothing to do with the Doppler effect. However, it is incorrect to state, as you did, that the fan rotation causes an intensity modulation (tremolo) that people falsely interpret as a modulation in pitch (vibrato). There REALLY IS a modulation in the pitch (!), and a vibraphone REALLY DOES produce a true vibrato -- hence the name. However, there is also a periodic alternation in the volume level associated with the opening/occlusion of the resonator, and this also introduces a tremolo. So BOTH things are happening at the very same time: pitch and amplitude modulation. The proper interpretation of what's actually going on has, in fact, been somewhat controversial in the vibraphone world. You will find online sources that swear it's one or the other. It's both. But again, it's not Doppler-related, either way.

[Teak]

Strictly speaking, the physics in your response is not correct. Yes, there will be a Doppler effect. The sound that reflects off a moving surface that is advancing directly towards the source with velocity, v, will return Doppler-shifted in frequency, approximately according to:

[change in frequency of the reflected sound] = [frequency at the source]*(v/c),

where c is the speed of sound in air (about 300 m/s).

For the tip of a fan blade moving at, say, about 2 m/s, the maximal change in the reflected frequency is therefore about 2 parts in 300, or 0.6%. A note of A440 Hz will change by +3 Hz to A443 Hz, which can be heard as a different pitch!

This has certainly turned into an interesting thread.

[Mandoplumb]

I'm no scientist, I don't claim to know what is happening but if I stand directly under a revolving ceiling fan and play the mandolin I hear the "beats" just as if the strings are not exactly twinned.

[sblock]

I'm no scientist, I don't claim to know what is happening but if I stand directly under a revolving ceiling fan and play the mandolin I hear the "beats" just as if the strings are not exactly twinned.

Yup. But I would take that as only possible evidence of a Doppler modulation of the frequency (not intensity) of the reflected sound. Only a tiny frequency difference can actually produce beats, because beats occur, as we all know, at a rate equal to the frequency difference between two rather similar notes. You can't really hear beats that are any slower than about 0.2 Hz (a period of 5 sec), nor can you hear beats that are much faster than about 20 Hz (a period of 0.05 sec). So for this to be the correct explanation, the fan must be modulating the reflected sound by somewhere between 0.2 and 20 Hz, and more likely, by just a few Hz (say, 2-10 Hz).

But an alternative possibility to consider is that it might not be a Doppler shift of the reflected frequency causing the apparent sensation of beats, after all, but simply a modulation of the intensity (and not the frequency) of the sound you hear in your ear as you play directly under the fan. As the wide blade passes immediately overhead, more sound reflects back to you off it. As the space between blades replaces it, less sound reflects. So you hear a louder-softer-louder alternation, and that would be pretty hard to tell from a true beat frequency, since they both produce the sensation of an intensity modulation of a few Hz.

One way to tell might be to move around to different places in the room. The beats you hear might get quieter in some spots, but if the beat rate doesn't change, but instead stays locked to the rotation speed of the fan, then you're probably dealing with an intensity modulation from the reflected sound, and not Doppler. So those are apparent "beats," but not true frequency-differential beats. However, if you move off to the side of the fan's axis and the beat rate increases just a bit, then you are almost certainly dealing with a Doppler effect, since the component of the velocity of the blade tip towards (and away) from you is greater when seen from the side of the fan than when seen face-on.

I'm betting that it doesn't matter, and this is not a true Doppler effect, but simply an effect of the reflecting fan blade passing overhead. But who knows? Someone needs to do the experiment and report back!! Ain't science wonderful?

[Larry Simonson]

Very occasionally I have heard pairs of singers produce produce a beat.

[Escaped Cellist]

What is all this talk about sound reflecting off of fan blades?

Elephant in the room: Sound waves are transmitted by a medium--in this case, air.

It's not just reflections - a ceiling fan is, by design, a mover and circulator of large quantities of air. The medium itself is being perturbed, while the transmission is occurring.

We do the same trick all the time by moving a string while it is vibrating. Hey ho, vibrato!

I'm not sure where armchair physicists come from, but it must be a lonely place if no one ever breathes there.

[Teak]

What is all this talk about sound reflecting off of fan blades?

Elephant in the room: Sound waves are transmitted by a medium--in this case, air.

It's not just reflections - a ceiling fan is, by design, a mover and circulator of large quantities of air. The medium itself is being perturbed, while the transmission is occurring.

We do the same trick all the time by moving a string while it is vibrating. Hey ho, vibrato!

I'm not sure where armchair physicists come from, but it must be a lonely place if no one ever breathes there.

Whatever the phenomenon, the rotating fan blades are clearly changing the way the instrument sounds to the player standing underneath. I used to live in the tropics and often played guitar underneath a rotating fan blade (before I bought air-con for that room). I noted that change in sound from directly under the fan to a spot off to the side. Of course, on afternoons that fan was on the highest speed I could put it on.

I don't understand how "air" is the elephant in the room. The Doppler shift does not occur only in a vacuum. Apparently this has been discussed in the piano forums also. http://forum.pianoworld.com/ubbthrea...e_triads_.html

And studied academically. (They used a computer fan in this case.) https://arxiv.org/ftp/arxiv/papers/1701/1701.04478.pdf

And for the record, I am an applied physicist to some extent (use physics in my work everyday). We use the Doppler shift phenomenon to measure the velocity of moving fluids. http://www.cclynch.com/products-cate...w-measurement/

But yeah, my office chair does have arms.

[Larry Simonson]

Play your mandolin out in an open field and then play it close to a hard wall and you will perceive a sound difference, That is, an instrument sounds different (to the player) depending how close they are to a reflector. Now if that reflector is periodically there and not there, like a fan, you may detect a difference when you move away from the fan.

[Cochiti Don]

I'm reminded of the silly M&M commercial talking into a table fan. That might be fun with a mando too!

[Bertram Henze]

What is all this talk about sound reflecting off of fan blades?

Elephant in the room: Sound waves are transmitted by a medium--in this case, air.

It's not just reflections - a ceiling fan is, by design, a mover and circulator of large quantities of air. The medium itself is being perturbed, while the transmission is occurring.

We do the same trick all the time by moving a string while it is vibrating. Hey ho, vibrato!

I'm not sure where armchair physicists come from, but it must be a lonely place if no one ever breathes there.

If moving air disturbs pitch, how are open air concerts even possible? Elephants stampeding the stage

Now back to my armchair...

[David L]

On to a different topic:

Also, the fans used in a vibraphone resonator are not really fans (although they're called this): their blades have no pitch! And your explanation is, unfortunately, therefore a bit off. These flat "fan" blades are simply there so that they alternately open and occlude the resonator openings at a fixed frequency (given by their rotation speed x number of blades). When the vibraphone resonators are partially blocked by the flat blades, their dominant resonant frequency (this is the so-called "organ pipe" frequency) is lowered, reducing the frequency of the note that's emitted by just a bit. The steady fan rotation leads to a fast, alternating opening-closure of the pipe, and thereby causes the pitch to waver, introducing a vibrato effect. And this has nothing to do with the Doppler effect. However, it is incorrect to state, as you did, that the fan rotation causes an intensity modulation (tremolo) that people falsely interpret as a modulation in pitch (vibrato). There REALLY IS a modulation in the pitch (!), and a vibraphone REALLY DOES produce a true vibrato -- hence the name. However, there is also a periodic alternation in the volume level associated with the opening/occlusion of the resonator, and this also introduces a tremolo. So BOTH things are happening at the very same time: pitch and amplitude modulation. The proper interpretation of what's actually going on has, in fact, been somewhat controversial in the vibraphone world. You will find online sources that swear it's one or the other. It's both. But again, it's not Doppler-related, either way.

I know that vibraphone discs are flat, that had nothing to do with what I said. How do the discs change the pitch? If you play the bar "open" and then play it "closed", the pitch is the same, just less volume. How does turning faster change that?

[sblock]

I know that vibraphone discs are flat, that had nothing to do with what I said. How do the discs change the pitch? If you play the bar "open" and then play it "closed", the pitch is the same, just less volume. How does turning faster change that?

We are wandering far from mandolin content...

Since you asked, I'll try to explain here how the fans (butterfly valves) can change the pitch.

Each note on a vibraphone is not being produced by a tuning fork, which is something with a very narrow, single resonant frequency, but by a wide aluminum bar, instead, which produces a complex spectrum of tones that's centered around a given note frequency, but actually has multiple frequencies. These bars actually vibrate in at least three main modes, in fact, and generate many nearby frequencies, with a great many higher overtones that are not simple rational fractions of the fundamental, which is very unlike a plucked string, and more akin to what happens when hitting a drumhead. Each bar is mounted over its own resonator (tube) that is tuned, by adjusting the tube length, to a frequency that is near the desired note value. The fan (butterfly valve) alternately closes and opens one end of the resonator tube. The resonator acts very much like the tube of an organ pipe, amplifying the fundamental frequency of the note (but not so much for the overtones; remember that the spectrum is broad and complex). When the resonator is closed at one end, its natural organ-pipe frequency is lowered. When is opened, it is raised. So the alternating valve produces a small modulation in the average pitch being amplified by the resonator. (The same thing happens when you open and close a hole near the end of a woodwind instrument, or cover and uncover its end, which is what you do when you play an Uilleann/Irish bagpipe. This action changes the pitch!) But closing the pipe ALSO produces a significant modulation in the volume, because the closed pipe can produce a stronger standing wave inside, which is louder than an open pipe. So we get a wavering modulation in the volume as well as the dominant pitch. This constitutes both a kind of "tremolo" (intensity modulation) and a kind of "vibrato" (frequency modulation) at the same time, but please remember that these Italian words are just over-simplifications, ported over from other kinds of instruments, where they are better defined and more applicable! They do not do proper justice to how the rotating fans and resonators continuously shape and reshape the sound spectrum of a vibraphone note as it's produced. I hope this answers the question.

Let me suggest that we now get back to mandolins.

[catmandu2]

Elephant in the room...

I'm not sure where armchair physicists come from, but it must be a lonely place if no one ever breathes there.

Can armchair metaphysicists weigh in on this one too?

[HonketyHank]

sblock, thanks for skipping the mathematical part. I'm a bit rusty there.