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Post by antigua on Mar 26, 2017 20:12:46 GMT -5
Note: if you're just seeing this thread for the first time, I'd like to refer you to this later test guitarnuts2.proboards.com/post/81045/thread , as it avoids use of an EBow, which it was subsequently determined is not a good testing device.
********* This is an offshoot of this thread guitarnuts2.proboards.com/thread/7907/string-pickup-sample about pickup sensing widths. We were getting into pickup distance and string pull issues, so today I've been trying various tests with a pickup mounted in roughly the middle position of a Strat, exactly 10.9mm in from the bridge, right over a node of the 6th harmonic. For the test, I drove the string with with an EBow placed over the 12th fret, so that it reinforced fundamental movement, and not those of the harmonics. Due to the use of the EBow, the analysis has no transient energy, only sustained. The string of subject is an open G string. The graphs below are made with the Velleman PCSGU250's spectrum analysis mode, set to persist so that samples overlap. I tried various tests involving the pickup itself, such as various pole piece strengths, but came upon a finding that had less to do with the pickup, and more to do with magnetic pull in general, so that's what is presented below. It appears to me that pole piece strength, most likely, simply determines the amount of string pull that occurs. Based on various tests, it appears to me that when a magnet is close to the string, the vibrational energy of the string is drawn to the portion of the string where the magnet is, at the expense of the rest of the string. Additionally, if the magnet is over the antinode of a particular harmonic, that particular harmonic will get a boost at the expense of other harmonics. It's similar to what happens when you perform a pinch harmonic, where all the energy is taken from the fundamental, and partially transferred to that harmonic that is "pinched out". For starters, here's the noise profile, these spikes represent background noise: No sound For this test, the pickup is a rather large distance from the string, 9mm, and it has three neo buttons, for a flux density of 600 gauss at the other end, roughly equivalent to an AlNiCo 2 pole piece. This shows the string vibrating under the power of the EBow, with the fundemental at 196Hz, and not yet being toyed with by a near by neodymium magnet. No interference Due to the placement of the pickup 10.9mm from the bridge, it's over an anti node of the 3rd harmonic, so the 3rd harmonic has a higher amplitude than the 2nd. Now, if I put a neo close to the string, over the 5th fret, overall power is lost from the other side of the string, where the pickup is located. Notice though, that by magnetically tugging on the anti node of the second harmonic over the 5th fret, the 2nd harmonic gained energy, while the fundemental and the 3rd and higher harmonics all lost energy. Tugging at 5th fret But if I move the neo magnets even further towards the end of the fret board, over the 1st fret, the 2nd harmonic now becomes very small, while the 3rd and 4th harmonics gain energy: Tugging at 1st fret Next, I try placing the neodymium close to the string on the pickup's side. Here the neo is over the neck pickup, which is symmetrical to the 5th fret. Notice now, that the side of the string where the pickup is located is being tugged at, the fundamental and the 2nd harmonic have higher amplitude: Tugging over neck pickup Next, "tugging" at the string directly over the bridge, which is opposite the first fret. Tugging over the bridge pickup Compare this to the 1st fret shot, and you can see that this strong tugging over the bridge pickup doesn't merely dampen the 2nd harmonic, but nearly eliminates it completely. The fact that some 2nd harmonic survived with the neo over the 1st fret says that the second harmonic still exists on the other side of the string, but over here where the neo is applied, it gets wiped out. Also notice that the 3rd harmonic has a high amplitude, and that the fundamental and 3rd harmonic have overall higher amplitudes. It shows that energy is being retained both at the side of the string where the magnetic pull is applied, but that the specific harmonics that are being pulled at show higher amplitudes than ones that are not. Notice too that many higher harmonics are teased out, and to a greater degree than was observed by pulling at the first fret Hypothesis:The implication is that, by having a pickup close to the strings, the magnetic pull attracts vibrational energy to it's local segment of the string, drawing energy away from the rest of the string. This test used a fixed vibration, but when a string is plucked, it initially comes closer to the magnet, but less so as it loses energy. Therefore a plucked string would start out by having a high degree of pull, but would "release" the string as the vibration dissipates. The harmonic effect the pickup has on the string, as a result of magnetic pull, is also contingent on the nodes, but more so the anti-nodes, that the pickup is placed under. In general, it would favor the harmonics that are already most prominent for that pickup, since those are the ones that displace the most in that particular location. The pull of the neodymium is also a lot stronger than that of a pickup, so the effects are exaggerated in the test, but it's all matters of degrees with magnetic fields, so these same effects will happen even with extremely weak magnets, though not to the same degree. A pickup with a stronger magnetic pull, such as one with AlNiCo 5 in place of a lower AlNiCo, would exhibit more of energy attracting behavior. Pickups with steel pole pieces tend to have a lower flux density and less "pull" than pickups with AlNiCo pole pieces, but there are two coils side by side, which might have the same overall effect as one string. I'll see if I can think up a test that would demonstrate this, one way or the other. It would be nice to determine how much more or less string pull occurs for AlNiCo 2/3/4 versus AlNiCo 5. Here's a pic of the test setup: 
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Post by stratotarts on Mar 27, 2017 8:43:21 GMT -5
I'm still digesting this. It's very compelling and has some interesting ramifications. Just one thing that bothers me - the Ebow works by feeding back the signal from the string, I think. So the output is affected by the signal it receives. That might be exaggerating the harmonic amplitudes by means of feedback. I think it would be preferable to drive the Ebow with a fixed frequency generator to highlight the proportions more exactly.
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Post by Deleted on Mar 27, 2017 10:15:24 GMT -5
VS Ceramic?
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Post by antigua on Mar 27, 2017 11:28:33 GMT -5
I'm still digesting this. It's very compelling and has some interesting ramifications. Just one thing that bothers me - the Ebow works by feeding back the signal from the string, I think. So the output is affected by the signal it receives. That might be exaggerating the harmonic amplitudes by means of feedback. I think it would be preferable to drive the Ebow with a fixed frequency generator to highlight the proportions more exactly. Some aspects of the test are completely arbitrary, but the important thing is whether or not the arbitrary test answers any questions. The strength, position of and magnitude of effects are all arbitrary. What matters is that they happen, that there's an asymmetry that favors the side of the string with the magnetic pull, and more particularly, the harmonics whose anti nodes are most immediately within the pull of the magnet. That's a good point about the EBow being designed to reinforce it's input, and that might have a) led to some suppression of of the 2nd harmonic, since it's anti node is under the EBow, and b) caused over representation of the fundamental, since the EBow is over it's sole "anti node". As far as I can tell, there's not reason the EBow would help or hurt the overall weighting phenomena that's observed with the magnetic pull, since the EBow is centrally positioned along the string. |
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Post by stratotarts on Mar 27, 2017 14:50:29 GMT -5
I'm still digesting this. It's very compelling and has some interesting ramifications. Just one thing that bothers me - the Ebow works by feeding back the signal from the string, I think. So the output is affected by the signal it receives. That might be exaggerating the harmonic amplitudes by means of feedback. I think it would be preferable to drive the Ebow with a fixed frequency generator to highlight the proportions more exactly. Some aspects of the test are completely arbitrary, but the important thing is whether or not the arbitrary test answers any questions. The strength, position of and magnitude of effects are all arbitrary. What matters is that they happen, that there's an asymmetry that favors the side of the string with the magnetic pull, and more particularly, the harmonics whose anti nodes are most immediately within the pull of the magnet. That's a good point about the EBow being designed to reinforce it's input, and that might have a) led to some suppression of of the 2nd harmonic, since it's anti node is under the EBow, and b) caused over representation of the fundamental, since the EBow is over it's sole "anti node". As far as I can tell, there's not reason the EBow would help or hurt the overall weighting phenomena that's observed with the magnetic pull, since the EBow is centrally positioned along the string. Sure, mainly this would just affect the exact ratio of the amplitudes, what I suggest is just a small refinement. It raises a point... a pull at antinodes has an effect of increasing some harmonics, yet the antinodes are exactly the places where some harmonics are suppressed in the output ... this means that there are some very complicated relationships to explore. |
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Post by antigua on Mar 27, 2017 15:32:10 GMT -5
Some aspects of the test are completely arbitrary, but the important thing is whether or not the arbitrary test answers any questions. The strength, position of and magnitude of effects are all arbitrary. What matters is that they happen, that there's an asymmetry that favors the side of the string with the magnetic pull, and more particularly, the harmonics whose anti nodes are most immediately within the pull of the magnet. That's a good point about the EBow being designed to reinforce it's input, and that might have a) led to some suppression of of the 2nd harmonic, since it's anti node is under the EBow, and b) caused over representation of the fundamental, since the EBow is over it's sole "anti node". As far as I can tell, there's not reason the EBow would help or hurt the overall weighting phenomena that's observed with the magnetic pull, since the EBow is centrally positioned along the string. Sure, mainly this would just affect the exact ratio of the amplitudes, what I suggest is just a small refinement. It raises a point... a pull at antinodes has an effect of increasing some harmonics, yet the antinodes are exactly the places where some harmonics are suppressed in the output ... this means that there are some very complicated relationships to explore. I'm not sure what you mean, exactly. Does something in particular look off? One implication is that raising and lowering a pickup won't greatly change the harmonic makeup seen by that pickup, because it's bringing energy to the harmonics that are already the most energetic, in that specific location. Although, I believe the attraction of energy towards itself might favor the lower harmonics. If I raise the neck pickup while listening with the neck pickup, I'm only expecting at best, to see an even rise in lower harmonics, therefore, a test I would like to try later is to take a Strat, sample from the neck pickup with the bridge and middle pickups lowered. I would then raise the middle and neck and see if doing so causes an increase in higher harmonics, as seen from the neck pickup, by drawing energy to those harmonics, as well as the pickup's side of the string. Conversely, if bridge or middle are monitored, and I raise the neck pickup, I should see an increase in all but the the 4th harmonic. |
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Post by ms on Mar 27, 2017 15:49:27 GMT -5
Antigua, this is really interesting, you did a great job of doing and explaining this. I want to start by understanding in more detail what an eBow does. In a few words, in samples the string vibration and then uses that signal to further drive the string with a coil in phase so that the amplitude increases.
Looking with a bit more detail, it appears that the amplitude is limited when its amplifier saturates. But when it saturates, it produces harmonics. It seems that it makes both even and odd, and so I think it does not saturate symmetrically. The power in the harmonics goes down with frequency, but also it is harder to excite harmonics because the higher the harmonic, the more more string bending (dissipation of energy) there is for the same amplitude of oscillation. With those two factors multiplying together, maybe you just get significant power in a few lower harmonics. So that agrees with your spectral plots. Does this sound right?
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Post by antigua on Mar 27, 2017 16:00:01 GMT -5
Antigua, this is really interesting, you did a great job of doing and explaining this. I want to start by understanding in more detail what an eBow does. In a few words, in samples the string vibration and then uses that signal to further drive the string with a coil in phase so that the amplitude increases. Looking with a bit more detail, it appears that the amplitude is limited when its amplifier saturates. But when it saturates, it produces harmonics. It seems that it makes both even and odd, and so I think it does not saturate symmetrically. The power in the harmonics goes down with frequency, but also it is harder to excite harmonics because the higher the harmonic, the more more string bending (dissipation of energy) there is for the same amplitude of oscillation. With those two factors multiplying together, maybe you just get significant power in a few lower harmonics. So that agrees with your spectral plots. Does this sound right? As I understand it, an EBow jas an exciter coil and a pickup inside. The exciter is simply connected to the pickup with an amplifier in between, so as to induce feedback. They say they had to design the EBow carefully so that the string would be the feedback intermediary, and not the EBow itself. I'm not sure what you mean by the saturation harmonics; there's no guitar amp involved, no gain or clipping. All the harmonics are cleanly generated by the string. The pickup is mounted above the guitar string, and connected to the Velleman oscilloscope with nothing in between. |
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Post by ms on Mar 27, 2017 16:25:38 GMT -5
Antigua, this is really interesting, you did a great job of doing and explaining this. I want to start by understanding in more detail what an eBow does. In a few words, in samples the string vibration and then uses that signal to further drive the string with a coil in phase so that the amplitude increases. Looking with a bit more detail, it appears that the amplitude is limited when its amplifier saturates. But when it saturates, it produces harmonics. It seems that it makes both even and odd, and so I think it does not saturate symmetrically. The power in the harmonics goes down with frequency, but also it is harder to excite harmonics because the higher the harmonic, the more more string bending (dissipation of energy) there is for the same amplitude of oscillation. With those two factors multiplying together, maybe you just get significant power in a few lower harmonics. So that agrees with your spectral plots. Does this sound right? As I understand it, an EBow jas an exciter coil and a pickup inside. The exciter is simply connected to the pickup with an amplifier in between, so as to induce feedback. They say they had to design the EBow carefully so that the string would be the feedback intermediary, and not the EBow itself. I'm not sure what you mean by the saturation harmonics; there's no guitar amp involved, no gain or clipping. All the harmonics are cleanly generated by the string. The pickup is mounted above the guitar string, and connected to the Velleman oscilloscope with nothing in between. Any amplifier has limited power and generates harmonics when you hit that limit. You could devise an automatic gain control circuit that would stop it from hitting the limit, but this is a small hand held device pretty much unchanged since 1969. It seems unlikely it does anything more complicated that simply hitting its head. But I really do not know. Where do the harmonics in your second plot come from if not the eBow when you make almost only the fundamental by exciting at the center of the string? I do not think the string can generate them from the fundamental. |
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Post by antigua on Mar 27, 2017 16:38:17 GMT -5
As I understand it, an EBow jas an exciter coil and a pickup inside. The exciter is simply connected to the pickup with an amplifier in between, so as to induce feedback. They say they had to design the EBow carefully so that the string would be the feedback intermediary, and not the EBow itself. I'm not sure what you mean by the saturation harmonics; there's no guitar amp involved, no gain or clipping. All the harmonics are cleanly generated by the string. The pickup is mounted above the guitar string, and connected to the Velleman oscilloscope with nothing in between. Any amplifier has limited power and generates harmonics when you hit that limit. You could devise an automatic gain control circuit that would stop it from hitting the limit, but this is a small hand held device pretty much unchanged since 1969. It seems unlikely it does anything more complicated that simply hitting its head. But I really do not know. Where do the harmonics in your second plot come from if not the eBow when you make almost only the fundamental by exciting at the center of the string? I do not think the string can generate them from the fundamental. That's an interesting thought. I suppose you're right, and that would explain why the third harmonic is higher amplitude than the second. The EBow is over the 2nd harmonic node, where it does nothing, and over the 3rd harmonic anti node, where it can do a lot. Even though there is that bias, the EBow is still in the middle, so any effect it has upon one side, it also has on the other. Therefore, any observation with respect to asymmetry still hold true. Instead of an EBow, I can also try vibrating the guitar, though that generates less amplitude, making it harder to measure differences. |
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Post by stratotarts on Mar 27, 2017 18:07:37 GMT -5
Yes, it's likely that the Ebow uses some kind of limiter circuit so that the oscillations don't become excessive and drive the string into a buzz. It could be a simple clipping circuit, or else it could be something that stays linear like a compressor.
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Post by ms on Mar 27, 2017 18:32:56 GMT -5
Yes, it's likely that the Ebow uses some kind of limiter circuit so that the oscillations don't become excessive and drive the string into a buzz. It could be a simple clipping circuit, or else it could be something that stays linear like a compressor. Patent no. 4075921 from 1978 shows an op amp driving a col. No diode clipping or other limiting is shown as far as I can see. It appears that it just saturates. |
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Post by antigua on Mar 28, 2017 23:48:36 GMT -5
I've been doing some testing with the EBow, but realized I'm having some trouble getting the same results by plucking that I got with the EBow, so I'm worried that the harmonic production on the part of the EBow is messing with the test results. I'm going to have to find another way to excite the strings, as the peculiarities of the EBow will forever cloud any results that are derived with it. I still think it fundamentally stands to reason that string pull effects are going to disproportionately impact the lower wound strings, because they have lower tension / less stiffness, and less permeable mass, so when looking for any string pull effect, it should be expected that the effect will be seen the most with the low E, and the least with the high E, which follow with the "Stratitus" problem usually effecting the larger wound strings more than any other. Another thing I noticed while testing, an EBow only induces vertical movement in the string: Viewed head on:    |
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Post by JohnH on Mar 29, 2017 13:52:35 GMT -5
I still think it fundamentally stands to reason that string pull effects are going to disproportionately impact the lower wound strings, because they have lower tension / less stiffness, and less permeable mass, so when looking for any string pull effect, it should be expected that the effect will be seen the most with the low E, and the least with the high E, which follow with the "Stratitus" problem usually effecting the larger wound strings more than any other. Id just like to chip in on that point, since I don't think that is correct. In a balanced set of strings such as 10-46, all the tensions are reasonably close, around the range 6.5 to 8.5 kg of force. It depends which core wire is used. The tension sets the apparent stiffness of the string for plucking, so within the same margins, they all feel consistent. The variation in their tones comes from the mass added either by larger plain diameter or the added winding mass. Here are some tests: courses.physics.illinois.edu/phys406/Student_Projects/Fall00/DAchilles/Guitar_String_Tension_Experiment.pdfWhen I work the maths on string vibration, without inputting specific string characteristics for each string, I start with assuming all strings have the same force. |
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Post by antigua on Mar 29, 2017 14:37:01 GMT -5
I still think it fundamentally stands to reason that string pull effects are going to disproportionately impact the lower wound strings, because they have lower tension / less stiffness, and less permeable mass, so when looking for any string pull effect, it should be expected that the effect will be seen the most with the low E, and the least with the high E, which follow with the "Stratitus" problem usually effecting the larger wound strings more than any other. Id just like to chip in on that point, since I don't think that is correct. In a balanced set of strings such as 10-46, all the tensions are reasonably close, around the range 6.5 to 8.5 kg of force. It depends which core wire is used. The tension sets the apparent stiffness of the string for plucking, so within the same margins, they all feel consistent. The variation in their tones comes from the mass added either by larger plain diameter or the added winding mass. Here are some tests: courses.physics.illinois.edu/phys406/Student_Projects/Fall00/DAchilles/Guitar_String_Tension_Experiment.pdfWhen I work the maths on string vibration, without inputting specific string characteristics for each string, I start with assuming all strings have the same force. I mentioned both the permeable mass and the stiffness, so I'm not saying it was only due to stiffness. I didn't know string makers made an effort to balance the stiffness, and it appears that there is variability there, too. If the string ends up being lower tension, for whatever reason, it will be more easily contorted by a magnet. In any event, any magnetic pull effect will favor the lower wound strings, so it makes sense to use them as a point of comparison when trying to determine if an effect is related to string pull, or something else. |
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Post by wgen on Mar 30, 2017 4:23:53 GMT -5
This is an offshoot of this thread guitarnuts2.proboards.com/thread/7907/string-pickup-sample about pickup sensing widths. We were getting into pickup distance and string pull issues, so today I've been trying various tests with a pickup mounted in roughly the middle position of a Strat, exactly 10.9mm in from the bridge, right over a node of the 6th harmonic. For the test, I drove the string with with an EBow placed over the 12th fret, so that it reinforced fundamental movement, and not those of the harmonics. Due to the use of the EBow, the analysis has no transient energy, only sustained. The string of subject is an open G string. The graphs below are made with the Velleman PCSGU250's spectrum analysis mode, set to persist so that samples overlap. I tried various tests involving the pickup itself, such as various pole piece strengths, but came upon a finding that had less to do with the pickup, and more to do with magnetic pull in general, so that's what is presented below. It appears to me that pole piece strength, most likely, simply determines the amount of string pull that occurs. Based on various tests, it appears to me that when a magnet is close to the string, the vibrational energy of the string is drawn to the portion of the string where the magnet is, at the expense of the rest of the string. Additionally, if the magnet is over the antinode of a particular harmonic, that particular harmonic will get a boost at the expense of other harmonics. It's similar to what happens when you perform a pinch harmonic, where all the energy is taken from the fundamental, and partially transferred to that harmonic that is "pinched out". For starters, here's the noise profile, these spikes represent background noise: No soundFor this test, the pickup is a rather large distance from the string, 9mm, and it has three neo buttons, for a flux density of 600 gauss at the other end, roughly equivalent to an AlNiCo 2 pole piece. This shows the string vibrating under the power of the EBow, with the fundemental at 196Hz, and not yet being toyed with by a near by neodymium magnet. No interferenceDue to the placement of the pickup 10.9mm from the bridge, it's over an anti node of the 3rd harmonic, so the 3rd harmonic has a higher amplitude than the 2nd. Now, if I put a neo close to the string, over the 5th fret, overall power is lost from the other side of the string, where the pickup is located. Notice though, that by magnetically tugging on the anti node of the second harmonic over the 5th fret, the 2nd harmonic gained energy, while the fundemental and the 3rd and higher harmonics all lost energy. Tugging at 5th fretBut if I move the neo magnets even further towards the end of the fret board, over the 1st fret, the 2nd harmonic now becomes very small, while the 3rd and 4th harmonics gain energy: Tugging at 1st fretNext, I try placing the neodymium close to the string on the pickup's side. Here the neo is over the neck pickup, which is symmetrical to the 5th fret. Notice now, that the side of the string where the pickup is located is being tugged at, the fundamental and the 2nd harmonic have higher amplitude: Tugging over neck pickupNext, "tugging" at the string directly over the bridge, which is opposite the first fret. Tugging over the bridge pickupCompare this to the 1st fret shot, and you can see that this strong tugging over the bridge pickup doesn't merely dampen the 2nd harmonic, but nearly eliminates it completely. The fact that some 2nd harmonic survived with the neo over the 1st fret says that the second harmonic still exists on the other side of the string, but over here where the neo is applied, it gets wiped out. Also notice that the 3rd harmonic has a high amplitude, and that the fundamental and 3rd harmonic have overall higher amplitudes. It shows that energy is being retained both at the side of the string where the magnetic pull is applied, but that the specific harmonics that are being pulled at show higher amplitudes than ones that are not. Notice too that many higher harmonics are teased out, and to a greater degree than was observed by pulling at the first fret Hypothesis:The implication is that, by having a pickup close to the strings, the magnetic pull attracts vibrational energy to it's local segment of the string, drawing energy away from the rest of the string. This test used a fixed vibration, but when a string is plucked, it initially comes closer to the magnet, but less so as it loses energy. Therefore a plucked string would start out by having a high degree of pull, but would "release" the string as the vibration dissipates. The harmonic effect the pickup has on the string, as a result of magnetic pull, is also contingent on the nodes, but more so the anti-nodes, that the pickup is placed under. In general, it would favor the harmonics that are already most prominent for that pickup, since those are the ones that displace the most in that particular location. The pull of the neodymium is also a lot stronger than that of a pickup, so the effects are exaggerated in the test, but it's all matters of degrees with magnetic fields, so these same effects will happen even with extremely weak magnets, though not to the same degree. A pickup with a stronger magnetic pull, such as one with AlNiCo 5 in place of a lower AlNiCo, would exhibit more of energy attracting behavior. Pickups with steel pole pieces tend to have a lower flux density and less "pull" than pickups with AlNiCo pole pieces, but there are two coils side by side, which might have the same overall effect as one string. I'll see if I can think up a test that would demonstrate this, one way or the other. It would be nice to determine how much more or less string pull occurs for AlNiCo 2/3/4 versus AlNiCo 5. Here's a pic of the test setup: I find this post especially interesting. If the harmonics sampling analysis revealed, for the most part, that it is particularly focused above the pole pieces of pickups, and so some of the Tillman model theories should be revisited at least, here you have explained a much more evident effect. Now, as you said, we should consider that the particular setup used for the testing could have somehow exaggerated the effects that are clearly visible in the graphs, but still. If the trend is what is here, my understanding is that a pickup close to the strings may impact the tone quite considerably, because it seems that those harmonics, typical of that area of the strings above that pickup, are boosted some, in respect to the others. Have I understood right? I'd like to ask a question about the graph where you had the magnet above the bridge pickup: I can clearly see an emphasis of the 3rd harmonic, but it seems to me that some higher harmonics are boosted some, too, just next to the 3rd harmonic (I'm not referring to background noises, which are much at the right hand of the spectrum, as you pointed out earlier in the post). Could you please tell me which frequencies are those, around which frequencies we have some of the emphasis I'm seeing, apart from the 3rd harmonic..? I'm saying this because it seems to me that there are some spikes there, too. Thank you very much in advance! |
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Post by antigua on Mar 30, 2017 11:45:39 GMT -5
I find this post especially interesting. If the harmonics sampling analysis revealed, for the most part, that it is particularly focused above the pole pieces of pickups, and so some of the Tillman model theories should be revisited at least, here you have explained a much more evident effect. Now, as you said, we should consider that the particular setup used for the testing could have somehow exaggerated the effects that are clearly visible in the graphs, but still. If the trend is what is here, my understanding is that a pickup close to the strings may impact the tone quite considerably, because it seems that those harmonics, typical of that area of the strings above that pickup, are boosted some, in respect to the others. Have I understood right? I'd like to ask a question about the graph where you had the magnet above the bridge pickup: I can clearly see an emphasis of the 3rd harmonic, but it seems to me that some higher harmonics are boosted some, too, just next to the 3rd harmonic (I'm not referring to background noises, which are much at the right hand of the spectrum, as you pointed out earlier in the post). Could you please tell me which frequencies are those, around which frequencies we have some of the emphasis I'm seeing, apart from the 3rd harmonic..? I'm saying this because it seems to me that there are some spikes there, too. Thank you very much in advance! I'm not sure how the EBow is messing with the results, because I don't have an alternative to contrast against. I tried vibrating the strings from the bridge, but they don't move enough. I've tries plucking the strings in a consistent way, but then it's difficult to tell what effect is happening when in relation to the transient and decay. I still have ideas, though. All the harmonics are harmonics of "G", periods of 196Hz, so the 2nd is 392Hz, 3rd is 588Hz, 4th is 784Hz, etc. I think if I can repeat this test without an EBow, it will be more clear what's happening. Unless someone out there happens top already know, and can share with us. The harmonic balance is largely dependent on where you pluck the string, and if you pluck near the bridge, you get a lot of higher harmonics because you're initiating vibration with an asymmetrical displacement that favors the smaller/higher harmonic divisions / modes of the string, at the expense of the wider/lower harmonic divisions, and the same sort of thing appears to happen with a strong magnetic pull; an asymmetrical pull closer to the ends of the strings seems to boost smaller divisions, and vice versa. |
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Post by Charlie Honkmeister on Mar 30, 2017 12:35:21 GMT -5
Since the E-Bow itself has a pickup, what's being picked up, amplified, and re-injected into the string, depends on the E-Bow pickup position on the string. So you already have an initial signal having a spectrum with peaks and nulls, before you magnetically transduce a higher power version of that signal back into the string at a slightly different location.
If you want to eliminate possible harmonic level inaccuracies because of the Ebow, it might make sense to use a piezo bridge saddle signal which has all harmonics present, and use it to drive a driver coil positioned at exactly 1/2 the speaking string length (first antinode.)
If you take things to the point that you want to see what happens on string pull versus magnetic field strength on an actual picking stroke to the signal output of the string, things will get complex in a hurry.
It would be fascinating to go there, but you would probably need an automatic picker, or a "pick-bot" to do that.
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Post by antigua on Mar 30, 2017 12:44:52 GMT -5
Since the E-Bow itself has a pickup, what's being picked up, amplified, and re-injected into the string, depends on the E-Bow pickup position on the string. So you already have an initial signal having a spectrum with peaks and nulls, before you magnetically transduce a higher power version of that signal back into the string at a slightly different location. If you want to eliminate possible harmonic level inaccuracies because of the Ebow, it might make sense to use a piezo bridge saddle signal which has all harmonics present, and use it to drive a driver coil positioned at exactly 1/2 the speaking string length (first antinode.) If you take things to the point that you want to see what happens on string pull versus magnetic field strength on an actual picking stroke to the signal output of the string, things will get complex in a hurry. It would be fascinating to go there, but you would probably need an automatic picker, or a "pick-bot" to do that. The frequency of a G string is 196Hz, is there some way to skip the feedback loop altogether and exciter the string into vibration with a function generator and coil? I'm not sure how much power it would take, or what kind of driver could would be ideal for the task. An EBow seems to benefit from the fact that it's causing a feedback loop, so I imagine an arbitrary excitation would require more power, and the string would need to be tuned very precisely, so that it's natural frequency is complimentary of the induced magnetic frequency. The difference from the EBow is that the hopefully the function driven exciter would only reinforce the fundamental and some odd harmonics, where as the EBow reinforces everything it sees. |
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Post by ms on Mar 30, 2017 14:52:57 GMT -5
Since the E-Bow itself has a pickup, what's being picked up, amplified, and re-injected into the string, depends on the E-Bow pickup position on the string. So you already have an initial signal having a spectrum with peaks and nulls, before you magnetically transduce a higher power version of that signal back into the string at a slightly different location. If you want to eliminate possible harmonic level inaccuracies because of the Ebow, it might make sense to use a piezo bridge saddle signal which has all harmonics present, and use it to drive a driver coil positioned at exactly 1/2 the speaking string length (first antinode.) If you take things to the point that you want to see what happens on string pull versus magnetic field strength on an actual picking stroke to the signal output of the string, things will get complex in a hurry. It would be fascinating to go there, but you would probably need an automatic picker, or a "pick-bot" to do that. The frequency of a G string is 196Hz, is there some way to skip the feedback loop altogether and exciter the string into vibration with a function generator and coil? I'm not sure how much power it would take, or what kind of driver could would be ideal for the task. An EBow seems to benefit from the fact that it's causing a feedback loop, so I imagine an arbitrary excitation would require more power, and the string would need to be tuned very precisely, so that it's natural frequency is complimentary of the induced magnetic frequency. The difference from the EBow is that the hopefully the function driven exciter would only reinforce the fundamental and some odd harmonics, where as the EBow reinforces everything it sees. If you want to drive it with a generator and amplifier instead, one way would be to use a set of closely spaced frequencies,, starting below the string resonance and moving up through it, performing separate spectral analyses on each. The responses at frequencies close to resonance (with and without the strong magnet) might be very interesting. Another thing would be to construct a signal containing a narrow range of frequencies about the resonance all at once, such as a tone modulated by narrow band random noise, and let the string decide what to do. |
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col
format tables
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Post by col on Mar 30, 2017 16:26:42 GMT -5
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Post by antigua on Mar 30, 2017 17:22:07 GMT -5
The polarity doesn't matter in terms of damping, because the string is permeable. It takes on the polarity of the magnet that is attracting it. It's like a refrigerator magnet; it sticks to the fridge either way. |
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Post by Charlie Honkmeister on Mar 31, 2017 12:53:18 GMT -5
Since the E-Bow itself has a pickup, what's being picked up, amplified, and re-injected into the string, depends on the E-Bow pickup position on the string. So you already have an initial signal having a spectrum with peaks and nulls, before you magnetically transduce a higher power version of that signal back into the string at a slightly different location. If you want to eliminate possible harmonic level inaccuracies because of the Ebow, it might make sense to use a piezo bridge saddle signal which has all harmonics present, and use it to drive a driver coil positioned at exactly 1/2 the speaking string length (first antinode.) If you take things to the point that you want to see what happens on string pull versus magnetic field strength on an actual picking stroke to the signal output of the string, things will get complex in a hurry. It would be fascinating to go there, but you would probably need an automatic picker, or a "pick-bot" to do that. The frequency of a G string is 196Hz, is there some way to skip the feedback loop altogether and exciter the string into vibration with a function generator and coil? I'm not sure how much power it would take, or what kind of driver could would be ideal for the task. An EBow seems to benefit from the fact that it's causing a feedback loop, so I imagine an arbitrary excitation would require more power, and the string would need to be tuned very precisely, so that it's natural frequency is complimentary of the induced magnetic frequency. The difference from the EBow is that the hopefully the function driven exciter would only reinforce the fundamental and some odd harmonics, where as the EBow reinforces everything it sees. It wouldn't be a problem to use a function generator signal to tune to the string frequency, at least for a very short time. Or, tune the string to the frequency generator. The problem is that you would have phase and frequency drift which would slide the exciting signal in and out of phase with the vibrating string. You would have to have a phase and frequency correction loop somewhere. That isn't necessarily a huge deal with some of the analog chips out there (e.g. CD4046 PLL) but maybe a bit much electronics hacking for the main thrust of what you're trying to do. Driving from a piezo string signal at the bridge, or a magnetic string signal picked up very close to the bridge, would be the most practical. Just as a possibility, and something I haven't done yet, is to take a pair of stereo earbuds, get one earbud, and inject Superglue into the center diaphragm part of the earbud. That fixes the coil in place, and you should end up with a single-string low impedance magnetic pickup. The output will be low mic level but a "normal" mic preamp should have enough gain to bring the signal up. That way you can use Blue-tac or something to fix it under the string of interest, and you have your signal to drive the exciter coil, with some power amplification, of course. |
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Post by antigua on Mar 31, 2017 15:18:44 GMT -5
It wouldn't be a problem to use a function generator signal to tune to the string frequency, at least for a very short time. Or, tune the string to the frequency generator. The problem is that you would have phase and frequency drift which would slide the exciting signal in and out of phase with the vibrating string. You would have to have a phase and frequency correction loop somewhere. That isn't necessarily a huge deal with some of the analog chips out there (e.g. CD4046 PLL) but maybe a bit much electronics hacking for the main thrust of what you're trying to do. Driving from a piezo string signal at the bridge, or a magnetic string signal picked up very close to the bridge, would be the most practical. Just as a possibility, and something I haven't done yet, is to take a pair of stereo earbuds, get one earbud, and inject Superglue into the center diaphragm part of the earbud. That fixes the coil in place, and you should end up with a single-string low impedance magnetic pickup. The output will be low mic level but a "normal" mic preamp should have enough gain to bring the signal up. That way you can use Blue-tac or something to fix it under the string of interest, and you have your signal to drive the exciter coil, with some power amplification, of course. I'm not exactly sure what is required to create a driver coil. Does it have to be low impedance or high? How much voltage? What shape? Core material? I have another idea to try, I tried arbitrary vibration from a back massager, that didn't work, but I do have an acoustic exciter I can try, which is supposed to somehow turn surfaces into speakers, and if I set that to pump out 196Hz, it might cause enough sympathetic vibration in the G string in order to get good test results. |
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Post by ms on Mar 31, 2017 15:56:54 GMT -5
It wouldn't be a problem to use a function generator signal to tune to the string frequency, at least for a very short time. Or, tune the string to the frequency generator. The problem is that you would have phase and frequency drift which would slide the exciting signal in and out of phase with the vibrating string. You would have to have a phase and frequency correction loop somewhere. That isn't necessarily a huge deal with some of the analog chips out there (e.g. CD4046 PLL) but maybe a bit much electronics hacking for the main thrust of what you're trying to do. Driving from a piezo string signal at the bridge, or a magnetic string signal picked up very close to the bridge, would be the most practical. Just as a possibility, and something I haven't done yet, is to take a pair of stereo earbuds, get one earbud, and inject Superglue into the center diaphragm part of the earbud. That fixes the coil in place, and you should end up with a single-string low impedance magnetic pickup. The output will be low mic level but a "normal" mic preamp should have enough gain to bring the signal up. That way you can use Blue-tac or something to fix it under the string of interest, and you have your signal to drive the exciter coil, with some power amplification, of course. I'm not exactly sure what is required to create a driver coil. Does it have to be low impedance or high? How much voltage? What shape? Core material? I have another idea to try, I tried arbitrary vibration from a back massager, that didn't work, but I do have an acoustic exciter I can try, which is supposed to somehow turn surfaces into speakers, and if I set that to pump out 196Hz, it might cause enough sympathetic vibration in the G string in order to get good test results. The impedance should be such that the driving amplifier can efficiently couple power into it. For example, the eBow as described in the patent uses a general purpose IC op amp, which might supply 5Ma at 12volts, so a couple K impedance. For tests such as proposed, I would use a power amp and a low impedance coil that would self resonate above the audio band, just to keep things simple. |
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Post by antigua on Mar 31, 2017 16:04:56 GMT -5
The impedance should be such that the driving amplifier can efficiently couple power into it. For example, the eBow as described in the patent uses a general purpose IC op amp, which might supply 5Ma at 12volts, so a couple K impedance. For tests such as proposed, I would use a power amp and a low impedance coil that would self resonate above the audio band, just to keep things simple. Do you think 12 volts is sufficient in this case, given that it's enough for an EBow, or does the fact that this won't exploit feedback increase the power demand? |
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Post by antigua on Apr 1, 2017 3:41:47 GMT -5
I'm having luck vibrating the string via sympathetic resonance using this audio exciter www.amazon.com/gp/product/B004AR5G9O/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 What I have to do is set the guitar on "feet" so that the vibration is retained in the body and neck of the guitar, otherwise the table the guitar is placed on eats up too much of the energy. I rested the head stock directly on the exciter device, which delivers vibration energy to the guitar a lot more efficiently than attaching the device from the top, which is more how it's intended to be used. With the exciter tuned to the exact frequency of the string, it gets a pretty rigorous vibration, and the nice thing is that it's a very pure string movement, extremely still looking with no inter modulations of any sort. You can tell that it's favoring fundamental movement and not exciting much harmonic movement, but there is enough harmonic content there to be useful. I also tried an exciter coil, but at 10 volts it was just barely moving the string, so I'd have to either get a stronger amp, or make a better coil. One annoying thing is that when the exciter coil's core was magnetized, like a pickup, this causes a lot more string movement, but then the introduction of the magnetic field sort of spoils the experiment, though I could see string pull over dead center as be "neutral" in that it's pull is perfectly symmetrical. |
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Post by ms on Apr 1, 2017 6:50:10 GMT -5
The impedance should be such that the driving amplifier can efficiently couple power into it. For example, the eBow as described in the patent uses a general purpose IC op amp, which might supply 5Ma at 12volts, so a couple K impedance. For tests such as proposed, I would use a power amp and a low impedance coil that would self resonate above the audio band, just to keep things simple. Do you think 12 volts is sufficient in this case, given that it's enough for an EBow, or does the fact that this won't exploit feedback increase the power demand? No problem. Gain in the circuit to make the feedback cause oscillation is one thing; power needed to drive the string is another. That holds whether or not you use feedback. Also, I think the EBow uses less than I said. "Normal" op amp supplies back then were +/- 15V, allowing about 12 or 13 volts (possibly more in some amps) positive and negative. The eBpw uses a 9 volt battery, and I think it always did. It does not hurt to allow use a bit more power than necessary. It gives more flexibility in what you can do, and you do not have to turn it up more than needed. |
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Post by Charlie Honkmeister on Apr 1, 2017 11:03:04 GMT -5
I'm having luck vibrating the string via sympathetic resonance using this audio exciter www.amazon.com/gp/product/B004AR5G9O/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 What I have to do is set the guitar on "feet" so that the vibration is retained in the body and neck of the guitar, otherwise the table the guitar is placed on eats up too much of the energy. I rested the head stock directly on the exciter device, which delivers vibration energy to the guitar a lot more efficiently than attaching the device from the top, which is more how it's intended to be used. With the exciter tuned to the exact frequency of the string, it gets a pretty rigorous vibration, and the nice thing is that it's a very pure string movement, extremely still looking with no inter modulations of any sort. You can tell that it's favoring fundamental movement and not exciting much harmonic movement, but there is enough harmonic content there to be useful. I also tried an exciter coil, but at 10 volts it was just barely moving the string, so I'd have to either get a stronger amp, or make a better coil. One annoying thing is that when the exciter coil's core was magnetized, like a pickup, this causes a lot more string movement, but then the introduction of the magnetic field sort of spoils the experiment, though I could see string pull over dead center as be "neutral" in that it's pull is perfectly symmetrical. Exciter coils shouldn't be a big issue. Just use the same one as you use for pickup testing. If you had a problem with 10 volts barely moving the string, the problem was current, not voltage. You have to get good current drive for the thang to work. The one I use is a plastic Strat bobbin without magnets/poles, and I had about 200 turns of #32 AWG on it. If you know the inductance and resistance of the exciter coil we could figure out the impedance. Parts Express and SparkFun have small speaker level power amp modules. Realistically, any small amp PCB capable of over about 100 milliwatts into 4-8 ohms should be fine. If the audio exciter on the headstock works for you , that's great. Your own Sustainiac Model C, in a way. |
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Post by antigua on Apr 1, 2017 11:52:11 GMT -5
I'm having luck vibrating the string via sympathetic resonance using this audio exciter www.amazon.com/gp/product/B004AR5G9O/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 What I have to do is set the guitar on "feet" so that the vibration is retained in the body and neck of the guitar, otherwise the table the guitar is placed on eats up too much of the energy. I rested the head stock directly on the exciter device, which delivers vibration energy to the guitar a lot more efficiently than attaching the device from the top, which is more how it's intended to be used. With the exciter tuned to the exact frequency of the string, it gets a pretty rigorous vibration, and the nice thing is that it's a very pure string movement, extremely still looking with no inter modulations of any sort. You can tell that it's favoring fundamental movement and not exciting much harmonic movement, but there is enough harmonic content there to be useful. I also tried an exciter coil, but at 10 volts it was just barely moving the string, so I'd have to either get a stronger amp, or make a better coil. One annoying thing is that when the exciter coil's core was magnetized, like a pickup, this causes a lot more string movement, but then the introduction of the magnetic field sort of spoils the experiment, though I could see string pull over dead center as be "neutral" in that it's pull is perfectly symmetrical. Exciter coils shouldn't be a big issue. Just use the same one as you use for pickup testing. If you had a problem with 10 volts barely moving the string, the problem was current, not voltage. You have to get good current drive for the thang to work. The one I use is a plastic Strat bobbin without magnets/poles, and I had about 200 turns of #32 AWG on it. If you know the inductance and resistance of the exciter coil we could figure out the impedance. Parts Express and SparkFun have small speaker level power amp modules. Realistically, any small amp PCB capable of over about 100 milliwatts into 4-8 ohms should be fine. I have a coil I'd like to use with a DC resistance of 52.8 ohms, and the inductance is 0.67 mH, it must be about 150 turns of 41 AWG. That one is ideal because it's small and would be easy to position, but I also have a plastic Strat bobbin coil with 3.2 ohms resistance and 0.49mH inductance, which is much larger, about 70 turns of 26 AWG. I'm slightly worried about burning out the 41 AWG coil by exposing it to too much current. What do you think about a little amplifier like this www.amazon.com/Pyle-PCA1-30-Watt-Stereo-Amplifier/dp/B0012KZNP4/ref=sr_1_4?s=electronics&dd=lydIXCa_3W4e95ktHPGr5g%2C%2C&ie=UTF8&qid=1491065510&sr=1-4&keywords=small+audio+amplifier&refinements=p_90%3A8308920011 ? These are the specs of the PCSGU250 function generator I'm working with now: amplitude range: 100mVpp to 10Vpp @ 1KHz// 600ohm load / 0V offset offset: from 0 to -5V or +5V max. (resolution 0.4% of full scale) vertical resolution: 8 bits square wave rise/fall time: 0.2µs sample rate: 12.5MHz typical sine wave distortion (THD): < 1% output impedance: 50ohm frequency range: from 0.005Hz to 500kHz I also have one of these that I can break out: www.gratten.eu/featured/atten-atf20b-20mhz-dds-function-generator.html , the specs for this are listed as * Power Supply: AC220V (1±10%) * AC110V (1±10%) (Pay attention to the voltage selection on rear panel) * Frequency:50Hz (1±5%) * Power Consumption: < 45VA * Operating Temperature: 0°C to +40°C * Operating Humidity: 80% R.H * Operation Characteristics: Keypad operation and rotary knob operation * Display: TFT display, 320*240 * Weight: 3.5kg |
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