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Johnmasters

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Don't try to understand what this guy is saying, but he puts simple waveforms through a Phase Shifter. You can just listen to the links, they will play on your windows media player.

Consider a sawtooth wave, which the bowed string is supposed to be [close to]. It is a Fourier sum of overtones. It is easy to make an electronic phase shifter to shift these overtones by different amounts according to their frequencies. The relative amplitudes of the overtones are not changed with the proper cirquit. The effect is the same as putting different time delays to the component Fourier contributions.

What one gets will not look at all like a sawtooth and apparently does not sound like one. I think the examples on this sight are of synthesizer keyboards. But as I gather, the initial signal is a simple sawtooth. I think this should interest some of you.

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Hi John,

Yes, I found this interesting.

I think there is probably phase shifting already happening with violins because of reflection of sound from the room. This phase shifting is probably enhanced by high frequency directional radiation, which tends to change direction with frequency. (think vibrato)

Very good musicians seem to be able to generate and control some of these features. Another factor is when a violinist 'emotes' and moves around while playing, this also enhances phase shifting and greater amount of directionality

Interesting topic

Oded

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I haven't had time to read the full thread that Michael links to, but clearly, phase shifts between wave forms produce a change in the resultant total waveform, and may certainly be audible. Itchycoo Park, anyone?

Maybe the discussion in the thread was about the ability of the ear to detect an absolute phase shift rather than a relative shift compared to another waveform? I could imagine that folks might be sceptical about this.

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I think we had this discussion a few months ago, and the acoustics experts assured me that phase shifts wouldn't make any difference in sound because ears are incapable of recognizing the effects of phase differences. :-) The discussion.

Based on designing and listening to very good audio equipment, I have to disagree with that contention. In what is called a "transient perfect" loudspeaker design, you are unlikely to hear much difference in music involving very few musicians, most of the sound for a given instrument coming from one speaker driver at a time. As the music increases in complexity and number of musicians, in a "transient perfect" design" the silence between notes becomes more distinct, transients are sharper and most notably, very low spl sounds are clarified. As an example, on my transient perfect speakers I can hear every time Isaac Stern breathes on the Beetoven concerto. On my Klipsch speakers, his breaths are just part of the background noise. This is just what you would expect when sound signals at different frequencies are not delayed by different amounts of time. The average person, who does not obsess over phase shifts in his crossovers ( :) ) will never notice.

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I suspect "phase shift" may mean different things to different people when discussing whole-instrument overtones.

For Violin acoustics, let's state some of the obvious:

(1) Each string's harmonic overtones are a function of its fundamental frequency;

(2) The bowed-string waveform is the realtime "input" to the whole instrument;

(3) The whole-instrument "output" [frequency response] is a function of its "input";

(4) IF there's measured phase shift between string "input" & whole-instrument "output" [frequencies], then there IS an acoustic mismatch.

For instrument design, you could create phase shift(s) anywhere you want.

Jim

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It is interesting to note that in general;

Everything we discuss here becomes a contest, of one sort or another.

I guess that's just the way it is.

No contests, just different experiences, interests and points of view about it all. Gawd knows I couldn't argue with Michael about anything having to do with violins.

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I think we had this discussion a few months ago, and the acoustics experts assured me that phase shifts wouldn't make any difference in sound because ears are incapable of recognizing the effects of phase differences.

I'll have to agree with this (it can happen :) )

Anyone who wants to try a perfect phase shifter and see if it makes any difference, try this:

Listen to someone playing a violin in an open space or a room without too much reflected sound. Move your head toward the violin by 12" (0.3 m for those of you in the modern world). That will shift the phase of an open A (440) by 141 degrees; the first overtone (880) will shift by 282 degrees; the next overtone (1320) will shift by 422 degrees. Does the violin sound radically different, with these overtones skewed all over the place?

Also interesting: the upbow and the downbow produce different pressure wave combinations (look at the trace from a microphone on an oscilloscope). The trace is inverted depending on bow direction. I defy anyone to hear the difference, even though it is easily measurable.

Regarding the website referenced in John's initial post, there is an awful lot of jargon comprehensible only to those who really are into these acoustic/electric effects. What is actually going on with the sample sound clips is clear as mud, but I would bet there is a lot more than just shifting the phases of a tone based on frequency.

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Regarding the website referenced in John's initial post, there is an awful lot of jargon comprehensible only to those who really are into these acoustic/electric effects. What is actually going on with the sample sound clips is clear as mud, but I would bet there is a lot more than just shifting the phases of a tone based on frequency.

I would like to have seen a schematic of what this phase shift circuit is; from what I can gather he is using Vactrols, which have an inherent characteristic delay before changing resistance, both when initially receiving light, and again when the light is removed. This alone doesn't sound like a phase coherent device. Delay is what causes phase differences.

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I think we had this discussion a few months ago, and the acoustics experts assured me that phase shifts wouldn't make any difference in sound because ears are incapable of recognizing the effects of phase differences. :-) The discussion.

I recall that. I also know that the common knowledge is that the ear is not sensitive to phaseshift distortion. That does not mean that it cannot be heard and does not have some effect. For example, speaker crossovers pay attention to phase shift and various people have tried to minimize it. It may not be a big deal, but it is looked at by fussy people.

(One claim to fame of the Linkwitz-Riley crossover cirquit is that it preserves phase.)*

So for the hyper-fussy, perhaps phase distortion makes some difference. A violin sounds like a violin, but the hyperfussy like to grade them on a scale of bad to great. A violin sounds like a violin because it makes a filtered sawtooth wave. How to filter it ???

Another thing: power spectra throw out phase completely. The speakers I make after looking at frequency response; they sound very good. But the non-phase-shifting Magnaplaner speakers are better. And there seems only one thing unique about them. (It is not the larger radiating area, I made vertical arrays of speakers.)

Nobody considers phase distortion. Sherlock Holmes said to eliminate everything that did not answer the question (power spectra), and what was left is the answer. That is why I think that at least it should be considered to have role even if it cannot be measured so easily.

*Also, there is a big industry selling expensive lead wires to speakers. Is 20 guage wire enought to feed a speaker? I think it is more than enough, but some people want to minimize inductance. This would involve phase shifting. I think it is silly and don't believe people can hear a thing. But I am also sceptical about hearing differences amongst good violins. (Especially as played by ordinary players) But people buy these cables. Talk about hyper-fussy ... I think that some people may hear very small things.

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Hi John,

Yes, I found this interesting.

I think there is probably phase shifting already happening with violins because of reflection of sound from the room. This phase shifting is probably enhanced by high frequency directional radiation, which tends to change direction with frequency. (think vibrato)

Very good musicians seem to be able to generate and control some of these features. Another factor is when a violinist 'emotes' and moves around while playing, this also enhances phase shifting and greater amount of directionality

Interesting topic

Oded

I almost mentioned your name in the opening posting because you like to think of geometrical phase cancellation from radiation at different parts of the body. (This would be like a multipole expansion of radiation from an antenna array.) I am not speaking of this sort of thing or the radiation field. I am talking about the entire violin with strings-bridge-body being coupled. Before it is played.

There are a lot of types of mechanical reactance in a violin, I am sure. (The iimpedances that do not dissipate energy but do shift phases). Those Maggies are expensive in the store even before they get to the listening room. Same as violins.

Light construction may be important. My personal hobbyhorse is to try to maximize static strength through arching considerations. I am planning to make new FEA models to do this. I know from experience that the arch shape [probably] affects the compression strength of a top. I will report later. And I am not speaking of bridge force either.

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I haven't had time to read the full thread that Michael links to, but clearly, phase shifts between wave forms produce a change in the resultant total waveform, and may certainly be audible. Itchycoo Park, anyone?

Maybe the discussion in the thread was about the ability of the ear to detect an absolute phase shift rather than a relative shift compared to another waveform? I could imagine that folks might be sceptical about this.

I have an interest in DIY speaker forums. They all make a fuss about anything that is not a "wire with gain" and I don't think anything should be ignored at this stage.

I am told that you are an astrophysicist and certainly you have your maths. I have aimed this thread at people like you and the other scientists and engineers.

Think of those HIFI nuts... maybe they have something ........

At the level of discrimination we have for tone, yes, it seems that something may be heard from relative phase shifts. A sawtooth coupled to a complicated "speaker cone". Seems it should at least be looked into.

Please explain "Itchycoo park" reference. I am a Yank.

I think we had this discussion a few months ago, and the acoustics experts assured me that phase shifts wouldn't make any difference in sound because ears are incapable of recognizing the effects of phase differences. :-) The discussion.

Michael; please don't use smiley-face unless you are 100% sure of yourself... All sorts of things are handled in threads, over and over again. I don't think that a single thread can throw out this issue. It may be important enough to discuss ............many times. At least it may be useful to look at this in some way like Anders looks at spectra.

Based on designing and listening to very good audio equipment, I have to disagree with that contention. In what is called a "transient perfect" loudspeaker design, you are unlikely to hear much difference in music involving very few musicians, most of the sound for a given instrument coming from one speaker driver at a time. As the music increases in complexity and number of musicians, in a "transient perfect" design" the silence between notes becomes more distinct, transients are sharper and most notably, very low spl sounds are clarified. As an example, on my transient perfect speakers I can hear every time Isaac Stern breathes on the Beetoven concerto. On my Klipsch speakers, his breaths are just part of the background noise. This is just what you would expect when sound signals at different frequencies are not delayed by different amounts of time. The average person, who does not obsess over phase shifts in his crossovers ( :) ) will never notice.

The Klipsch are horns, aren't they? I read that horns are good for some things but not others. Are your "transient perfect" speakers electrostatic? I once had electrostatic earphones, and they were wonderfully amazing for clairity. I could hear a chair dropped backstage in the famous Heifetz recording of the Beethoven concerto. I listened to this recording a million times before and never heard it. In either the Heifetz Brahms or Beethoven, one could hear a subway train go beneath the building.

It is interesting to note that in general;

Everything we discuss here becomes a contest, of one sort or another.

I guess that's just the way it is.

And people like to make jokes. It is not clear if people are fur or aguin the idea.

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Listen to someone playing a violin in an open space or a room without too much reflected sound. Move your head toward the violin by 12" (0.3 m for those of you in the modern world). That will shift the phase of an open A (440) by 141 degrees; the first overtone (880) will shift by 282 degrees; the next overtone (1320) will shift by 422 degrees. Does the violin sound radically different, with these overtones skewed all over the place?

This is already filtered out by the brain because we are used to hearing violins in the radiation field. It does not say anything about phase distortion in the source. Besides, as you say, the phase shifts in the radiation field are completely simple and predictable. They are already pre-expected. I address this to Oded also.

Regarding the website referenced in John's initial post, there is an awful lot of jargon comprehensible only to those who really are into these acoustic/electric effects. What is actually going on with the sample sound clips is clear as mud, but I would bet there is a lot more than just shifting the phases of a tone based on frequency.

That is why I said don't read it, just listen to the recordings. I expect that the initial oscillator goes through a slow ramp, sawtooth, to simulate the decay of a piano note. (Backwards sawtooth)

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I have an interest in DIY speaker forums. They all make a fuss about anything that is not a "wire with gain" and I don't think anything should be ignored at this stage.

I am told that you are an astrophysicist and certainly you have your maths. I have aimed this thread at people like you and the other scientists and engineers.

Think of those HIFI nuts... maybe they have something ........

At the level of discrimination we have for tone, yes, it seems that something may be heard from relative phase shifts. A sawtooth coupled to a complicated "speaker cone". Seems it should at least be looked into.

Please explain "Itchycoo park" reference. I am a Yank.

I'm just a regular physicist, not an astro-type.

Itchycoo Park is a song by the Small Faces, famous for the (earliest?) use of the "phaser" effect on the organ in the middle 8.

I'm also a reformed hi-fi nut, which I find often places me on both sides of the fence when it comes to some of the discussions on this forum. For example I believe that:

1) Human hearing is capable of detecting effects that are very difficult if not impossible to measure with conventional instrumentation, but on the other hand;

2) The brain is very good of tricking you into imagining that you can hear effects/differences that do not really exist.

1) makes me sceptical about the value of acoustic measurements on violins relative to evaluation by listening

2) makes me sceptical about "playing in" and the whole Old Italian thing.

But then, if you accept 2) then of course it puts 1) on dodgy footing (and vice-versa), which is why I prefer not to think too much about these things (and why I'm a "reformed" hi-fi-nut!)

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I would like to have seen a schematic of what this phase shift circuit is; from what I can gather he is using Vactrols, which have an inherent characteristic delay before changing resistance, both when initially receiving light, and again when the light is removed. This alone doesn't sound like a phase coherent device. Delay is what causes phase differences.

Here is one. You can find other discussions if you google Phase Shift Circuit. It is a just a unit-gain opamp with a capacitor and resistor. I am going to make one and put it between my preamp and amp. Just to listen to solo violin.

The phase shift angle is a function of frequency, capacitance and resistance which is adjustable.

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I'm just a regular physicist, not an astro-type.

Itchycoo Park is a song by the Small Faces, famous for the (earliest?) use of the "phaser" effect on the organ in the middle 8.

I'm also a reformed hi-fi nut, which I find often places me on both sides of the fence when it comes to some of the discussions on this forum. For example I believe that:

a) Human hearing is capable of detecting effects that are very difficult if not impossible to measure with conventional instrumentation, but on the other hand;

:) The brain is very good of tricking you into imagining that you can hear effects/differences that do not really exist.

I am sceptical too, but I have to talk to these guys in their language. If there is spurious proof for excellence in tone, then lets talk about spurious explanations.

a) makes me sceptical about the value of acoustic measurements on violins relative to evaluation by listening

:) makes me sceptical about "playing in" and the whole Old Italian thing.

Again, I agree. Could be that old is good because of survival of the fittest. I liked my 1947 Becker, and it certainly did not sound "old" the way I played it (very mediocre). And I don't trust listeners, just what I hear when I play to myself.

But then, if you accept a) then of course it puts a) on dodgy footing, which is why I prefer not to think too much about these things (and why I'm a "reformed" hi-fi-nut!)

Money and accumulating junk has me out of the DIY speaker business. I am convinced now that I like my Maggies the best. But the experience was worthwhile. I was put in contact with some of the speaker-nut discussions. And they ARE a lot like what is on this forum.

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Here is one. You can find other discussions if you google Phase Shift Circuit. It is a just a unit-gain opamp with a capacitor and resistor. I am going to make one and put it between my preamp and amp. Just to listen to solo violin.

The phase shift angle is a function of frequency, capacitance and resistance which is adjustable.

I am well aware of phase shift in an amplifier. I was more interested in seeing what this fellow is doing by implementing a vactrol into the feedback loop. So far I fail to see how you would utilize this to glean any useful spectra information.

The phase shift angle is a function of frequency, capacitance and resistance which is adjustable. Capacitance and inductance parameters create phase shift due to the reactance of these components, a resistor can only alter the Q of either of these two.

I am going to make one and put it between my preamp and amp. Just to listen to solo violin.

Phase shift is meaningless unless referenced to another waveform at a specific point in time. If you build an broadband audio amplifier stage that shifts the phase equally across the spectrum, you won't hear any difference in the resulting audio unless you compare it to The original un-altered signal; All you have accomplished is delaying the signal. I'm not trying to discredit you, but what do you think you may learn from this?

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The Klipsch are horns, aren't they? I read that horns are good for some things but not others. Are your "transient perfect" speakers electrostatic? I once had electrostatic earphones, and they were wonderfully amazing for clairity. I could hear a chair dropped backstage in the famous Heifetz recording of the Beethoven concerto. I listened to this recording a million times before and never heard it. In either the Heifetz Brahms or Beethoven, one can hear a subway train go beneath the building.

I Have the Klipsch Forte speakers which have horn tweeter and midrange, 12" cone woofer plus 12" passive radiator for bass. My transient perfects are a three way system I designed using Scan-Speak drivers, 1" dome tweeter, 5" cone midrange, 10" cone woofer. Transient Perfect designs with cone drivers and passive crossovers are a particular problem because the drivers must be offset relative to each other in order to get the sound arriving at one point (10' away in my design) at the same time for all three drivers. That makes cabinet design difficult, particularly if wife approval is required. Note there is sound delay due to the offsets plus due to the roll-offs of the crossover components.

The real attraction of horns is that they produce very high spl for the input voltage and dynamic range is incredible. Normal drivers (cones, dome tweeters, etc.) suffer in transients due to their lack of sensitivity; A sudden surge in power heats the voice coil, resistance goes up and the coil heats, increasing the resistance and the thing just does not reproduce the change in spl associated with a transient. This is worst for the tweeter, thus taking the leading edge off of transient signals, so you have a non-linearity to deal with. Horns do transient spl changes spectacularly well. However, the great lengths of horns make it very difficult to use spatial offsets to properly create a transient perfect combined output. Your only reasonable approach is to use a digital crossover and separate amps for each driver, a new level of PITA. Further, tubeophiles object to having opamps between them and the source of output signal. Finally, electrostatic earphones give a reference to HiFi nuts as to what music actually sounds like as only one transducer is needed for the full range of music frequencies. There are no delayed signals to try to properly sum. You pay your money and you take your choice as to your favorite forms of distortion.

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