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Topic: Audibility of inverted polarity in real music (Read 48584 times) previous topic - next topic
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Audibility of inverted polarity in real music

Reply #25 –
OK, now I'm just confused on exactly what I did and exactly what could be supported. I'm quite certain I used Kernel Streaming, but I'm not sure if I resampled, or if I fed 44.1 into KS. I'd guess I did the former, probably with foo_pphs.

Audibility of inverted polarity in real music

Reply #26 –
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OK, now I'm just confused on exactly what I did and exactly what could be supported. I'm quite certain I used Kernel Streaming, but I'm not sure if I resampled, or if I fed 44.1 into KS. I'd guess I did the former, probably with foo_pphs.
[a href="index.php?act=findpost&pid=314369"][{POST_SNAPBACK}][/a]

If you used KS, then you should have gotten the below error unless you have PPHS or SSRC in your DSP chain. Anyway, try putting it into normal 2ch mode and removing any resamplers from the DSP chain. Probably won't make any difference to audiability, but if you can rule something out easily you may as well do so.

Audibility of inverted polarity in real music

Reply #27 –
I'm well aware of what it would look like.

Oh well, maybe I'll do this again sometime, but I'm not holding my breath. It's not a high priority for me to reproduce this, especially since nobody else is giving it a shot (wink wink).

Audibility of inverted polarity in real music

Reply #28 –
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If the equipment makes this audible, so what? That is irrelevant in the context of justifying phase correctness in mastering and playback.

The only possible argument that could be made is whether the wrong polarity is necessarily any worse than the correct polarity, which doesn't really weaken the importance of the results any. Nobody in the literature has even been able to ABX this on real music. Sine waves, sure, but not Primus. In fact, if this were an equipment issue, that might make the results more important, depending on if different amplifiers result in different levels of audibility. (It would to date be the first known way to objectively measure audible distortion with modern, properly functioning amplifiers.)

Axon, when we have equipment that makes something audible depending on phase, then we have faulty equipment. Not in a fatal sense, but in sense of not being completely transparent. Knowing that our equipment isn't perfect, how can we even consider arguing about audibility or correctness of phase?

Phase correctness in mastering and playback is a matter of standard. Its so trivially easy to maintain, that there is no justification whatsoever to phase reversal in the recording chain. I consider this part of the matter irrelevant. Incorrect phase on a recording is simply huge label of disgrace for the recording company. Its a sign of negligent attitude. What quality can you expect from a recording company that can't even get its phase (wires) right?

And the part of equipment that makes it audible is not amplifier, but electromechanical system, electromagnetic to acoustic transducer we call speaker. Headphones are less influenced, but still are too, especially those that have wild riding frequency and phase response.
Perhaps you heard cheap electrolytic capacitors with your 710, they can have asymmetric response.

The effect that bothers most is dependence of magnetic force on the cone as it is displaced from its rest position. Not only is the force lower to either side from the center, but it is also almost always *asymmetric*, which in quite many cases causes the cone to push out and stay offcenter, depending on the music material. Its there where phase reversal changes mechanical behaviour, and as being off the optimal position imparts distortion, the nature of distortion depends on where or how much the cone is displaced.

Have a glimpse of how bad it really is with speakers:
http://www.klippel.de/pubs/assesslargsign/...performance.pdf

Anyway, there is single strong argument against audibility of continuous phase changes - it happens all the time as you move in the space. If we were sensitive to phase, then we'd hear timbre of the world around us differently every time we moved our heads, every time we moved a footstep. That alone makes the race for perfect phase response a moot, imho.

Things we hear are really different distortions, not the phase reversal itself. Thus we can't really even know which of the two phase positions is closer to transparent - either could be wrong.
It really really did sound different. Not in a placebo way.

Audibility of inverted polarity in real music

Reply #29 –
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If the equipment makes this audible, so what? That is irrelevant in the context of justifying phase correctness in mastering and playback.

The only possible argument that could be made is whether the wrong polarity is necessarily any worse than the correct polarity, which doesn't really weaken the importance of the results any. Nobody in the literature has even been able to ABX this on real music. Sine waves, sure, but not Primus. In fact, if this were an equipment issue, that might make the results more important, depending on if different amplifiers result in different levels of audibility. (It would to date be the first known way to objectively measure audible distortion with modern, properly functioning amplifiers.)

Axon, when we have equipment that makes something audible depending on phase, then we have faulty equipment. Not in a fatal sense, but in sense of not being completely transparent. Knowing that our equipment isn't perfect, how can we even consider arguing about audibility or correctness of phase?

If that is your standard of perfection, then we must have a lot of defective hardware floating around. Much more than would be expected from the quantitative distortion measurements and ABX failures of various amplifiers.

Now, I do agree that your hypothesis is pretty likely, but at this point I can't discount the alternative hypothesis (that the effect is real and that some sources have other types of distortion that mask it). Do you have any suggestions on how to distinguish between the two cases? The only thing I can think of is to maybe put the card under the knife and measure its inverted/noninverted distortion with a good digitizer.

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Phase correctness in mastering and playback is a matter of standard. Its so trivially easy to maintain, that there is no justification whatsoever to phase reversal in the recording chain. I consider this part of the matter irrelevant. Incorrect phase on a recording is simply huge label of disgrace for the recording company. Its a sign of negligent attitude. What quality can you expect from a recording company that can't even get its phase (wires) right?

Actually, most audiophiles who care enough to look at the waveforms looking for proper phase have stated that most/all recordings in existence have wrong phase in at least one of their tracks. In other words, most music is recorded in both correct and incorrect phase.

A lot of highly innocuous things can mess up the polarity. Many (perhaps most) preamps invert phase, since inverting amplifier configurations as a rule of thumb have less noise than noninverting amps. Speakers are not necessarily wired for +/+ polarity.

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And the part of equipment that makes it audible is not amplifier, but electromechanical system, electromagnetic to acoustic transducer we call speaker. Headphones are less influenced, but still are too, especially those that have wild riding frequency and phase response.
Perhaps you heard cheap electrolytic capacitors with your 710, they can have asymmetric response.

Whoa there! You can't have it both ways. Either the transducers are the only source of the distortion, or the amplifier may possibly be the source of the distortion.  But the two statements are logically contradictory.

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The effect that bothers most is dependence of magnetic force on the cone as it is displaced from its rest position. Not only is the force lower to either side from the center, but it is also almost always *asymmetric*, which in quite many cases causes the cone to push out and stay offcenter, depending on the music material. Its there where phase reversal changes mechanical behaviour, and as being off the optimal position imparts distortion, the nature of distortion depends on where or how much the cone is displaced.

Have a glimpse of how bad it really is with speakers:
http://www.klippel.de/pubs/assesslargsign/...performance.pdf

Thanks, this is really good information. This is sort of corroborated by the fact that I need to listen at loud volumes to notice it. However, based on the rated specs of my headphones, I'd need to exceed 120dB SPL to exceed them, so the plausibility of this being an issue when my ears don't bleed after the test is not established.

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Anyway, there is single strong argument against audibility of continuous phase changes - it happens all the time as you move in the space. If we were sensitive to phase, then we'd hear timbre of the world around us differently every time we moved our heads, every time we moved a footstep. That alone makes the race for perfect phase response a moot, imho.

Things we hear are really different distortions, not the phase reversal itself. Thus we can't really even know which of the two phase positions is closer to transparent - either could be wrong.
[a href="index.php?act=findpost&pid=314531"][{POST_SNAPBACK}][/a]

Wrong. You are completely misunderstanding wave mechanics. You cannot invert phase by moving around in space, at least in the presence of a point or planar sound source.

I would explain why, but somebody on Head-Fi made the same mistake, and I and somebody else laid the smack down on him for several days and he never seemed to figure it out. So please ask if you want it.

The example is also quite flawed because I notice obvious changes in timbre as I move my head around, but that's due to HRTFs and pinna effects.

Audibility of inverted polarity in real music

Reply #30 –
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...since inverting amplifier configurations as a rule of thumb have less noise than noninverting amps...

In serious?  How could you do this?

Audibility of inverted polarity in real music

Reply #31 –
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It's all well and good in theory, but a lot of things happen that aren't supposed to so long as the possibility exists.

Which possibility? For your information; my statements HERE are not "possibilities" like either "black magic". They have been verified by engineers by more than 30 years, and they are basic laws of the electronics.
You responded to my post with evasive words, with the intention to turn aside the attention about your lack of knowledge about the topic.

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Moreover, the membranes and the attached coils suspended in the magnetic field, comprising your headphones or speakers, may also have greater elasticity/sensitivity with respect to bending outwards as opposed to inwards or vice versa, depending on how they are suspended -- just like your eardrums.
You still have not answered the headphone/speaker part. Care to exercise your basic knowledge in physics?

You are wrong again.
I didn't respond to this part of your post because I considered it irrelevant, not by another reason.
The good speakers and headphones are designed with the goal of to reproduce the music signal as faithfully as this is possible, and the only way to obtain this (for a mechanical device like a speaker) is that both movements (outwards and inwards) have similar elasticity/sensitivity behavior.

Audibility of inverted polarity in real music

Reply #32 –
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If that is your standard of perfection, then we must have a lot of defective hardware floating around. Much more than would be expected from the quantitative distortion measurements and ABX failures of various amplifiers.
And why would you think otherwise? And again, why do you keep the amplifier as the only equipment of interest? There are not many transducers whose THD is even in same order of magnitude with cheapest and crappiest 1-bit DAC or fullrange amplifier..

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I can't discount the alternative hypothesis (that the effect is real and that some sources have other types of distortion that mask it). Do you have any suggestions on how to distinguish between the two cases? The only thing I can think of is to maybe put the card under the knife and measure its inverted/noninverted distortion with a good digitizer.
First, we need to understand what we are looking for - what at all can make it possible to hear phase inversion, ie. turn to physiology of ear and hearing. Then we'd like to check whether limited recording chain is even capable of providing us with such signal, then we can think of method to detect fault in hardware, deal with it and evaluate hearing.

If you can point to specific place in your sample where you hear it, it would be nice to try to pinpoint it to very precise section of wav, extract it and analyze it. If it appears to be possible to reproduce with synthetic test signals, then we are onto something. We'd understand correlation to audibility. You could run that section through loopback test to try to detect measurable changes.

To try to capture the fault, I'd first try to make sure whole reproduction chain has same slew rate on both positive slope and negative slope. Depending on implementation it could go from perfect to awful. Price doesn't matter.

There are many faults that *could* be the cause, but of these many things *most* are inaudible. And hard to measure because they occur in specific dynamic conditions only, thus no formal generally accepted methodology exists.
Currently lots of debates are around transient distortions that are not measured with the THD methodology. They manifest only during fast changes of amplitude and spectrum, adding or delaying spectral components only for that transient duration. Perceived changes in pitch hint on phase modulation or pretty complex intermodulation distortion components near the fundamental you are listening to.

In terms of real audibility, I can only think of asymmetric nonlinearity inside our hearing organs that could *sometimes* trigger audibility of phase reversal. But it is so rare event that its completely pointless to chase.
If we could ABX phase reversal every single time we faced it, please, but if we have to seek for that incredibly rare example where its audible after an incredible effort and still with very arguable reliability, without slightest evidence its not due to hardware, then excuse me, we are chasing ghosts of pigs that maybe could have flied in their former life. This isn't empirical evidence, its ancedotal evidence.

Your own drastic difference in reliability to ABX your samples on differing hardware gives a straight hint that its about hardware, not ears. And you have ability to deductively find out which piece of equipment it is. Its not that some subaudiophile equipment is "masking" total absolute phase reversal, is it. How'd you mask something like that anyway?
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Actually, most audiophiles who care enough to look at the waveforms looking for proper phase have stated that most/all recordings in existence have wrong phase in at least one of their tracks. In other words, most music is recorded in both correct and incorrect phase.
And you believe this?

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A lot of highly innocuous things can mess up the polarity. Many (perhaps most) preamps invert phase, since inverting amplifier configurations as a rule of thumb have less noise than noninverting amps. Speakers are not necessarily wired for +/+ polarity.
But this is fancy playback chain, not recording..
Not that your points on most preamps or rule of thumb is true..
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And the part of equipment that makes it audible is not amplifier, but electromechanical system, electromagnetic to acoustic transducer we call speaker. Headphones are less influenced, but still are too, especially those that have wild riding frequency and phase response.
Perhaps you heard cheap electrolytic capacitors with your 710, they can have asymmetric response.
Whoa there! You can't have it both ways. Either the transducers are the only source of the distortion, or the amplifier may possibly be the source of the distortion.  But the two statements are logically contradictory.
Your logic sucks. For $25 you get what you pay for. Be happy that it has so increbily good sound for that money, but please don't take that for granted.
And 710 hardly qualifies as amplifier. I just offered you a possible extreme case of crappy component that certainly wouldn't be expected in $500+ amp but is *easily* acceptable in a pretty complex 8-channel device as 710 for $25. I mean, $3 per channel? Come on, you can barely get 8 cheapest RCA cables for that money.. and you expect to reliably evaluate physiology of hearing with that?

Of course amplifier *CAN* be audible source of distortions, I never said opposite. I said that most likely it isn't, that much higher distortion is produced with that last passive mechanical device. You can't be talking about real audibility until you can show that it is not the distortion of that last device you are hearing.

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http://www.klippel.de/pubs/assesslargsign/...performance.pdf

Thanks, this is really good information. This is sort of corroborated by the fact that I need to listen at loud volumes to notice it. However, based on the rated specs of my headphones, I'd need to exceed 120dB SPL to exceed them, so the plausibility of this being an issue when my ears don't bleed after the test is not established.
You focus on wrong thing. At loud volumes it becomes catastrophic - 30% THD and such. Look at the graphs and think of shapes - they are there at low volumes aswell, just smaller.

You'd want to observe how magnetic force is asymmetric, how it drops upon any kind of displacement off the rest position, how compliance is asymmetric. Finally notice how wildly the distortion depends on loudness, frequency - ie. dynamics. The paper doesn't even touch intermodulation distortion that motor creates depending on driving methods, etc. Its a mess. Headphones are quite different in any case - mechanics is very different. So you can't apply that paper directly to headphones. But they have their own list of problems.

But interesting where you got the 120db requirement for your phones? Do you have any data about displacement of membranes of your headphones? Do you have even remotely reliable data about their distortion I wonder?

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Anyway, there is single strong argument against audibility of continuous phase changes - it happens all the time as you move in the space. If we were sensitive to phase, then we'd hear timbre of the world around us differently every time we moved our heads, every time we moved a footstep. That alone makes the race for perfect phase response a moot, imho.

Things we hear are really different distortions, not the phase reversal itself. Thus we can't really even know which of the two phase positions is closer to transparent - either could be wrong.
Wrong. You are completely misunderstanding wave mechanics. You cannot invert phase by moving around in space, at least in the presence of a point or planar sound source.

I would explain why, but somebody on Head-Fi made the same mistake, and I and somebody else laid the smack down on him for several days and he never seemed to figure it out. So please ask if you want it.

The example is also quite flawed because I notice obvious changes in timbre as I move my head around, but that's due to HRTFs and pinna effects.
I believe you are not in position to judge my "complete misunderstanding" of wave mechanics. I'd suggest you to first make some effort to understand what other side means. And don't say that because I didn't write an essay you are free to assume whatever you like.
You assumed that I assumed that absolute phase inversion occurs. You assumed wrong.

Ever heard of room acoustics? Have you found a point source? Have you ever looked for correlation between magnitude of phase changes and perceptible timbre changes? There are works on that matter, and only very drastic and abrupt phase response changes are found to be audible. The rest goes into audiophile myth area.

Can you tell how much does phase of 10kHz wave changes wrt to say 200hz  when your distance to tweater changes 3cm while distance to woofer stays the same? And tell how obvious effect on timbre that has.

Evolution has arranged our hearing so that we are generally insensitive to absolute phase and to a large degree changes to phase of spectrum components so that we can recognize and distinguish sounds by timbre, and use phase of transient's envelope for localization. It would be distractive if timbre changed in proportion to phase changes. We wouldn't survive in the wild.

I hope you don't insist that phase response in your room doesn't change as you move? Total inversion is just very special case, not even relevant to timbre..
It really really did sound different. Not in a placebo way.

Audibility of inverted polarity in real music

Reply #33 –
Splitting up my reply into several parts.

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I believe you are not in position to judge my "complete misunderstanding" of wave mechanics. I'd suggest you to first make some effort to understand what other side means. And don't say that because I didn't write an essay you are free to assume whatever you like.
You assumed that I assumed that absolute phase inversion occurs. You assumed wrong.

I apologize for my tone there. I do admit it was out of line.

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Ever heard of room acoustics? Have you found a point source? Have you ever looked for correlation between magnitude of phase changes and perceptible timbre changes? There are works on that matter, and only very drastic and abrupt phase response changes are found to be audible. The rest goes into audiophile myth area.

Can you tell how much does phase of 10kHz wave changes wrt to say 200hz  when your distance to tweater changes 3cm while distance to woofer stays the same? And tell how obvious effect on timbre that has.

Evolution has arranged our hearing so that we are generally insensitive to absolute phase and to a large degree changes to phase of spectrum components so that we can recognize and distinguish sounds by timbre, and use phase of transient's envelope for localization. It would be distractive if timbre changed in proportion to phase changes. We wouldn't survive in the wild.

I hope you don't insist that phase response in your room doesn't change as you move? Total inversion is just very special case, not even relevant to timbre..
[{POST_SNAPBACK}][/a]

Ow. I thought for a while that maybe we were confusing phase with polarity, but after doing more research I realize the source of my confusion: I've always thought that waves reflected from surfaces are of the same polarity. After reading [a href="http://www.du.edu/~jcalvert/waves/soundwav.htm]this[/url], and remembering what happens to untaut lengths of string when you thwap them on one side and watch the reflection happen on the other side, I realize I was mistaken: reflected waves are of opposite polarity.

So you can consider my foot very firmly in my mouth right now 

If I assume that reflections are of the same polarity, then obviously you can't construct any situation with passive materials that would negate the polarity of a signal. Which completely explains our gap of opinion. Besides that I totally agree with you on the audibility of phase shifts and group delay. Short of pathological cases like standing waves, they are not that audible, if at all.

Audibility of inverted polarity in real music

Reply #34 –
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Evolution has arranged our hearing so that we are generally insensitive to absolute phase and to a large degree changes to phase of spectrum components so that we can recognize and distinguish sounds by timbre, and use phase of transient's envelope for localization. It would be distractive if timbre changed in proportion to phase changes. We wouldn't survive in the wild.[a href="index.php?act=findpost&pid=315193"][{POST_SNAPBACK}][/a]


Now, hold on there.

Pure time delay, also known as linear phase, would be very confusing indeed if we somehow could hear it. Of course, we don't hear pure time delay, and we don't even hear something that looks somewhat like a pure time delay over a critical bandwidth or so on the basilar membrane.

If you said "to some degree" in your comment on phase, I'd be content. We just had a rather substantial argument somewhere here about phase audibility.

Narrowband FM vs. AM (both have exactly the same power spectrum) do not sound the same, and you can demonstrate this trivially with Octave or Matlab. 

In that thread, there was also some dispute over the validity of Fourier Analysis, (sigh) but I don't think we have that problem in this thread.

The key, I think, is to learn to separate out the "delay" part from phase shift.  When you talk about moving to and from a speaker, you're simply performing a linear-phase behavior, and that's not going to change envelope, waveshape, etc, except by pure time delay, ergo that discussion is just not germain.

A germain change in phase is the same as having substantial dispersion in the signal, i.e. different frequencies get there at different TIMES.
-----
J. D. (jj) Johnston

Audibility of inverted polarity in real music

Reply #35 –
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Evolution has arranged our hearing so that we are generally insensitive to absolute phase and to a large degree changes to phase of spectrum components so that we can recognize and distinguish sounds by timbre, and use phase of transient's envelope for localization. It would be distractive if timbre changed in proportion to phase changes. We wouldn't survive in the wild.

Now, hold on there.

Pure time delay, also known as linear phase, would be very confusing indeed if we somehow could hear it. Of course, we don't hear pure time delay, and we don't even hear something that looks somewhat like a pure time delay over a critical bandwidth or so on the basilar membrane.
...
The key, I think, is to learn to separate out the "delay" part from phase shift.  When you talk about moving to and from a speaker, you're simply performing a linear-phase behavior, and that's not going to change envelope, waveshape, etc, except by pure time delay, ergo that discussion is just not germain.
I'm not sure what you say here. I was NOT talking about "moving to and from a speaker", nor about pure time delay.
About your narrowband FM/AM I'd like to discuss some more in your thread. But it is example of "very drastic and abrupt phase response changes".
It really really did sound different. Not in a placebo way.

Audibility of inverted polarity in real music

Reply #36 –
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Actually, most audiophiles who care enough to look at the waveforms looking for proper phase have stated that most/all recordings in existence have wrong phase in at least one of their tracks. In other words, most music is recorded in both correct and incorrect phase.
And you believe this?
[{POST_SNAPBACK}][/a]

OK, you've got me stumped again. Nobody seems to have actually pointed out "X recording was made in wrong polarity", and it's unclear to me how to clearly distinguish between wrong polarity and moving the mic to opposite where it was before.

[a href="http://www.positive-feedback.com/Issue6/brown.htm]Positive Feedback[/url] mentions a record which was flipped in polarity by the mastering engineer, which implies that either that rereleased LP or the original LP was in the wrong polarity. But that's kind of a pathological case.

I'm going to ask around and see if anybody knows of some known CDs with bad polarity, and I might try and identify reversal with vocals across multiple CDs, although I'm unsure of the soundness of that approach.

Audibility of inverted polarity in real music

Reply #37 –
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Which possibility? For your information; my statements HERE are not "possibilities" like either "black magic". They have been verified by engineers by more than 30 years, and they are basic laws of the electronics.

Actually, I was referring to the variability of characteristics and the probability of manufacturing defects that exists any time mass production is involved. No one tests every single transistor or chip; only a sample is tested -- and neither is it feasible to test the entire assembled device in all possible operation modes -- only to perform some basic tests to verify that the assembly is OK and that no components are failing outright.

And even though the variance in characteristics and the probability of failure of any individual component is fairly low, not enough to be noticeable without measuring instruments or operating the component outside the spec, when combined to a single device and given the amount of components involved in a typical piece of electronics, the probability of the whole device not behaving by design approaches 1 feairly quickly. Anyone who ever dealt anywhere near closely with any piece of electronics, analog or digital, knows that rarely does it work completely as expected. Sorry, but that's just about the only thing that has been "verified" by me personally in the past 15 years, so your reassuring words miss my ears.

"Possibility exists" in this case referred to negative feedback, which is a workaround for the problem rather than a solution for it -- and besides, you can only push it so far. The more feedback, the faster you converge, but the more you drive your gain down at the same time. The more you drive gain down, the more cascades you need, and the more cascades you need, the more non-linear distortions (which you are trying to compensate for) you have in the first place, no matter whether you loop the entire system or just the individual cascades. Besides, the more cascades you have, the more noise and positive feedback you have circling around in the power bus, hence the more filtering you need. Power filters are (were?) usually just RC filters rather than LC, and tend to displace the bias, making it more difficult to tune with the usual 5-10% variability in resistances. So -- not sure about now, but 10 - 20 years ago, finding the right amount of negative feedback (and the right amount of cascades) was a compromise between quality and performance. And since the basic principles of operation remain the same to this day, I doubt anything has drastically changed here -- maybe now you can use stabilizers in place of RC filters and operational amplifiers much more widely because you can put so much stuff on a chip.

One other thing we have not mentioned so far as "by design" behavior is concerned -- a number of factors that have a profound effect on the operation of semiconductors (especially in analog circuits) that are not completely under the designer's control, the most prominent ones being temperature and age -- which, even though they can be _somewhat_ compensated for with additional circuitry or toleranced, cannot truly be controlled for.

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You responded to my post with evasive words, with the intention to turn aside the attention about your lack of knowledge about the topic.

Intentions is an ambiguous matter because you can read between the lines in any text, and "find" meanings the original author never even thought about, but which in reality are your own wishful thinking. Intentions are therefore irrelevant for the purpose of this discussion; actions (and their immediate causes) are what matters. So let us cut the guesswork about each other's intentions and remain on topic please.

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The good speakers and headphones are designed with the goal of to reproduce the music signal as faithfully as this is possible, and the only way to obtain this (for a mechanical device like a speaker) is that both movements (outwards and inwards) have similar elasticity/sensitivity behavior.

That's right -- but in a perfect speaker, the magnet, the membrane, and the coil must be perfectly symmetric, and the area of the diffusor itself must be infinite -- which of course is not the case. Again designed with the goal, but in practice only approaching the goal. And just like with the transistor amplifiers, you can slap on some fixes to mask the problem, but not really fix it. Such, one might design a particular shape that would behave "reasonably" well in reproducing a wide range of frequencies "approximately" independent of the source and destination position; put a box around the outer edge of the membrane to prevent lower frequencies cancelling themselves, pick the shape of the box such that the resonances compensate for the speaker's otherwise lousy frequency response, etc, etc -- all that is being done, I don't doubt that. But there are simply too many factors involved (many of them outside the designer's control) to create anywhere near complete mathematical model and find an anywhere near perfect solution.

The explanations that others have put forth all (most?) sound reasonable, but I guess we'll never know whether it's hearing or equipment specifics that allow one to hear polarity inversion -- I still tend to think one as much as the other, especially that the majority of the reasons seem to be just plain physics rather than psychoacoustics. Probably the only thing made clear is that people have their DACs set to top notch, so digital->analog conversion is probably not the cause.

Audibility of inverted polarity in real music

Reply #38 –
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http://www.klippel.de/pubs/assesslargsign/...performance.pdf

Thanks, this is really good information. This is sort of corroborated by the fact that I need to listen at loud volumes to notice it. However, based on the rated specs of my headphones, I'd need to exceed 120dB SPL to exceed them, so the plausibility of this being an issue when my ears don't bleed after the test is not established.
You focus on wrong thing. At loud volumes it becomes catastrophic - 30% THD and such. Look at the graphs and think of shapes - they are there at low volumes aswell, just smaller.

You'd want to observe how magnetic force is asymmetric, how it drops upon any kind of displacement off the rest position, how compliance is asymmetric. Finally notice how wildly the distortion depends on loudness, frequency - ie. dynamics. The paper doesn't even touch intermodulation distortion that motor creates depending on driving methods, etc. Its a mess. Headphones are quite different in any case - mechanics is very different. So you can't apply that paper directly to headphones. But they have their own list of problems.

But interesting where you got the 120db requirement for your phones? Do you have any data about displacement of membranes of your headphones? Do you have even remotely reliable data about their distortion I wonder?
[a href="index.php?act=findpost&pid=315193"][{POST_SNAPBACK}][/a]

For my Etys, the max rated SPL is 122dB. I guess I pulled 120db out of my butt for the A900s (I do remember it being around 120) but I might be able to dig up the specs on that.

I would expect that the rated SPL is based on the highest loudness that doesn't distory, but if it's a semi-graceful degredation then perhaps that sort of criteria can't be perfectly established.

Audibility of inverted polarity in real music

Reply #39 –
So I brought up the question of known circumstances of inverted polarity on SteveHoffman.tv. Man, those guys are cagier than Head-Fi. Anyways, the conclusions I think I can make from that discussion are rather surprising.
  • Nobody can provide concrete proof of endemic polarity reversal that is either detectable on the CD or verified by the producer.
  • Moreover, the common consensus of two mastering engineers (Steve Hoffman and Clark Johnson) is that the polarity is pretty much impossible to determine objectively.
  • The only way that polarity should be determined, in their eyes, is subjectively, by determining which polarity sounds better.
  • Some OK anecdotal evidence for endemic polarity reversal: up until recently (if ever), microphones never had a standard XLR wiring scheme, and the hot wire could be in one of several places depending on the mic.
  • In another thread it was noted that the MFSL remaster of The Mothers of Invention's "We're Only In It For The Money" was inverted with respect to the earlier Rykodisc remaster.

Audibility of inverted polarity in real music

Reply #40 –
Quote
It has been found that ear is sensitive to positive pressure, negative pressure being ignored. [a href="index.php?act=findpost&pid=250388"][{POST_SNAPBACK}][/a]


Don't you mean positive displacement on the basilar membrane, after going through the "cochlear filter", rather?

In any case, I wonder if it's possible to instrument the headphones to find out just how well the reproduction and inverted reproduction track each other. I've not found many devices (some few headphones) that are linear enough to attempt a test like this. Most, especially on things that are abrubt in time, tend to respond differently to positive and negative excitation.

To that, add the fact that the air itself is quite nonlinear if the peaks get to any substantial level, and I'd be worried that the air, intself, is changing the stimulus at the eardrum. Once that happens, differences aren't very surprising.
-----
J. D. (jj) Johnston

Audibility of inverted polarity in real music

Reply #41 –
Quote
Some OK anecdotal evidence for endemic polarity reversal: up until recently (if ever), microphones never had a standard XLR wiring scheme, and the hot wire could be in one of several places depending on the mic.[a href="index.php?act=findpost&pid=317413"][{POST_SNAPBACK}][/a]


Sorry to be so late to the table here, but life is busy.

I must also note that if there are multiple microphones in the same soundfield, inverting one microphone will create substantially different filtering than it otherwise would.

I seem to recall the people doing "Perceptual Soundfield Reconstruction" stating that they had to be very sure that all of the mikes were wired and responding properly in terms of polarity, as well. That is, perhaps, less surprising.
-----
J. D. (jj) Johnston

Audibility of inverted polarity in real music

Reply #42 –
Quote
It really really did sound different. Not in a placebo way.
[a href="index.php?act=findpost&pid=313918"][{POST_SNAPBACK}][/a]

That has to be one of the most funny thing I've read on these forums   

Audibility of inverted polarity in real music

Reply #43 –
on polarity reversal in recordings:  it does happen, and fairly often.  don't know about CDs, but try ripping a DVD and comparing the audio tracks.

obviously we can expect 5.1 mixes to be a fair bit different to 2.0 mixes, as they are done at different times, and possibly by different people on different equipment.  however, absolute phase inversion is very often visible in places it shouldn't ought to be (centre channel of a 5.1 compared to 50/50 average of left and right in the 2.0 track).  i see this nearly every day.

also, dubbed and music/effects tracks are often in opposite phase, though different language dubs tend to be in the same phase (like english + japanese).  this can be spotted when playing a tape with 4 channels - full mix and music+effects.  on a DVW-A500 deck, there's a short crossfade when monitoring channels are switched.  with inverted polarity, this normally unnoticable crossfade becomes a dip in volume as the channels cancel out.  i've observed this a few times before, though i can't remember what on (how convenient )  mainly because i didn't care and wasn't looking for it.  this is obviously only relevant with newer material where the dub and M&E channels are in sample-accurate sync.

i'm not sure if the effect is present on this title, but it's the only one i can think of that has both M&E and dialogue mixes on it - the region 4 release of "Mars Attacks"

it's a real mixed bucket with video material.

Audibility of inverted polarity in real music

Reply #44 –
A Speculation Regarding Perception of Detail

I’ve observed that if an audio system sounds good, no single component of that system can be all that bad nor can the polarity of the recording be played inverted from the live performance.

I have come to this conclusion because I haven’t been able to compensate for a bad component without causing some egregious sonic and musical tradeoffs.  On the other hand, if a system really sounds awful it may only be a single component or the inverted polarity of the recording that’s causing the problem.  For example, simple as it may seem, a single component could degrade the sound if its power cord is plugged into the wall outlet in less than the best sounding orientation.

A great sounding system is the result of its creator’s choice of components and musical judgment.  The only true basis for their judgment is an understanding of music and a memory of unamplified acoustic instruments and voices in a reasonable acoustic venue and heard from an aesthetically correct distance.

I believe that every choice one makes in the design of an audio system involves tradeoffs, and the only question is which tradeoffs each of us finds acceptable.  Around fifteen years ago, when I first became interested in the audibility and importance of absolute polarity, the speaker system that I’d created some ten years earlier and used for all my serious testing and musical enjoyment had second-order 12 dB Linkwitz-Riley crossovers.  Despite its many advantages it also had one major disadvantage; it wasn’t phase coherent. Without phase coherence it was impossible for me to discern polarity or to hear music purely in or out of absolute polarity because that crossover requires some of its drivers to always play in opposite relative polarities to each other.  As a result that speaker system was inconsistent with the single absolute polarity of live music.  I listened to each separate driver connected first in one polarity and then the other.  It wasn’t all that easy in the beginning to hear the differences, especially with my sealed back electrostatic tweeters.  But since they crossed over at a relatively low 1.6 kHz I eventually decided that they, as well as all the other drivers, sounded better connected in absolute polarity.  And next, with all the drivers playing in absolute polarity, I determined that I greatly preferred hearing music in absolute polarity.  And from that day to this, I only find music played in absolute polarity to be truly emotionally satisfying and believe that the single most important sonic and musical aspect of a properly connected audio system is its ability to reproduce the polarity of live music.

Audio systems must at the very least satisfy the following three requirements to be suitable for rendering polarity judgments.  1. The playback polarity of the source is heard in the same polarity as the original recorded source.  2. The system is phase coherent and preferably minimum phase.  In the analog domain the only classic crossover networks that permit a speaker to preserve the phase-polarity of the input signal are 6 dB first-order Butterworth.  If you’re not sure about your speaker system, you may use single driver headphones.  3. The system’s frequency response deviates no more than  +/- 3 dB from flat between 50 and 8 kHz which is an example of an application of the rule of 400 as defined in the first edition of the Audio Cyclopedia.

The gist of my speculation regarding the perception of detail and polarity is as follows: When one watches film, video or computer monitors the pictures are not seen as a series of separate still images and thank goodness!  It’s because the frames change or refresh fast enough, typically 24, 30 or 60 plus times per second respectively.  The actual flash rate may be up to120 frames per second, depending upon the medium, which causes our eye-brain’s persistence of vision to merge one still frame of a picture into the next.

Similarly, in audio, active noise-canceling headphones illustrate the ear-brain’s persistence of hearing with regard to high frequencies.  The way that active noise-canceling headphones work is by picking up ambient noise with built-in microphones and then generating a signal that’s exactly out of phase to the ambient noise that, at least in principle, should cancel it completely.  The specifications of active noise-canceling headphones indicate that they cancel bass frequencies much more effectively than high frequencies.  And perhaps that’s true to some extent, but much of the reduction in their apparent effectiveness at higher frequencies may be the result of our ear-brain’s persistence of hearing that merges the rapidly alternating relative phase of high frequencies into one sound that has no apparent phase/polarity.  Thus two tweeters playing high frequencies out of relative phase aren’t heard as canceling each other. Perhaps, this phenomena could be considered a corollary of the Fletcher-Munson effect whose curves describe the reduction of our ear’s sensitivity at both frequency extremes.  Well wouldn’t it be great if noise-canceling headphones canceled the high frequencies as well as the bass frequencies?  I’d surely like that and I bet you would too.  So from Shakespeare – Julius Caesar, Cassius speaking, "The fault, dear Brutus, is not in our stars [equipment], but in ourselves…" 

In my experience it’s exceptionally difficult if not impossible to determine solely by ear the phase of a tweeter’s electrical connection because the phase of the high frequency signal reverses too rapidly for our ear-brain to get a fix on it.  In other words, when the highpass frequency of a tweeter is raised it eventually becomes so high that it exceeds our ear-brain’s ability to distinguish the phase of its electrical connection, and its rapid phase reversals merges both phases into a single sonic impression that’s without a discernable phase.  For example, when two tweeters are playing a 10 kHz signal, if your head is a mere 3/10ths of an inch (a quarter wavelength) closer to one tweeter than the other, the signal from one tweeter arrives at your ears 180 degrees out of phase with the signal from the other tweeter.  Although theoretically they should cancel each other perfectly, I believe most listeners will still hear the 10 kHz signal at full volume.

Before I state the conclusion of my theory you need to know something about the use of test equipment to determine polarity.  The measurements of spectral content, frequency balance, dynamic range, distortion made on components playing music are the same regardless of the polarity of its playback.  Were it otherwise, I wouldn’t have written this think piece about how music played out of absolute polarity affects our perception of detail.  According to "The Wood Effect" many listeners can detect the polarity of asymmetrical musical signals even though test equipment and computer programs can’t.  Therefore it shouldn’t seem so contrary to common sense, scientific analysis or the least bit mysterious that measurements frequently don’t correlate well with subjective listening tests.  But on the other hand, perhaps some measurements will be more relevant to the way we hear when equipment is played in absolute polarity!

Now it follows, although the cutoff threshold may vary among individual listeners, as the sound’s frequency increases, above some point all listeners will perceive the music’s high frequencies as equally loud regardless of their actual polarity.  But when music is heard out of absolute polarity, the midrange, bass, and even the high frequencies below some frequency, all tend to sound somewhat recessed, rather dry, and bleached out.  Thus psycho-acoustically against a background of a sucked out and a papery dry sounding midrange, and a sucked out dry sounding bass, the high frequencies are heard in bold relief and sound a bit harsh, which also makes the bass and mid-range seem more detailed with faster transients, although they are not.  And that can make the bass sound as if its attacks are quicker because what’s heard as the leading edge of its transients are really the sound of its harmonics which are actually reproduced by the mid-range and tweeter not the woofer.  The result gives the impression of a greatly degraded stereo image that’s rather two-dimensional with a soundstage that’s vaguely focused and somewhat confused.  But those effects are really only psychoacoustic artifacts of the music being played out of absolute polarity and not how acoustic instruments and voices sound live!

Here are some other examples of how the psychoacoustics of audio affects our perceptions, which sometimes seems counter intuitive, but nevertheless may resonate with some listeners.  I believe when you add a subwoofer to a system it doesn’t necessarily sound as if you’ve added more bass, but more often than not, it sounds as if the highs have been reduced.  Similarly, add a super tweeter to a system and it may sound as if there’s less bass not more highs.  And if you turn off the bass/mid-bass altogether or reduce your mid-range, the sound seems more detailed when it’s not.

Music played out of phase coherence or out of absolute polarity may cause some listeners to wrongly attribute the low fidelity unpleasant sound to solid state devices or the digital process in general.  This causes some listeners to prefer what they think is the more tuneful, full bodied, and rounded sound that they associate with tube equipment or vinyl records which they believe sounds more like a live performance, when in point of fact, all they really need to hear is music played in absolute polarity.  High-fidelity equipment, tube or solid state, shouldn’t impose a sonic character of its own on the musical signal; its only tasks are to amplify the signal without distortion and control the speakers!  How much tweaking and component swapping in our systems are only musically misinformed attempts to correct for music played out of absolute polarity that in Absolute Reality are bound to fail the test of high-fidelity?  Does this suggest that the conclusions of some prior listening tests should be reevaluated and repeated with music that we know for sure is played in absolute polarity?  I definitely think so, and that should include recordings as well, but each of you may answer that question for yourselves.


The Louis Objective Test of the Audibility of Relative Polarity

Someone, other than the test subject, compiles a 72-minute test CD-R or CD of 72 one-minute music tracks as follows: The first track will be a one-minute excerpt from a CD, record or tape recording of a two microphone stereo recording selected for its musical value but without regard to its actual polarity.  The second track will be the same one-minute excerpt as the first track, but it will be recorded in the same polarity as the first track or in the opposite relative polarity to the first track as determined by the toss of a coin, heads the same and tails in the opposite polarity.  The same procedure is followed for tracks 3 and 4 with different music and repeated again until 36 pairs of identical music tracks have been recorded to the CD for a total of 72-minutes.  The person making the disc memorializes the polarity of each of the even numbered tracks relative to its odd numbered counterpart, and thus he has created a test CD for The Louis Objective Test of the Audibility of Relative Polarity.  The playback system should use single driver headphones or at least a speaker system with consistent polarity, i.e. all drivers move in the same relative phase to each other.  The actual polarity of any track or the playback system doesn’t affect the validity of the test because it’s only a test of the audibility of relative polarity not absolute polarity.  A test of a person’s ability to discern the actual polarity isn’t necessary if they can’t pass the relative polarity test.  However, test subjects who prove they discern absolute polarity would obviously pass a relative polarity test.

There’s also The Louis Objective Test of the Audibility of Absolute Polarity, but unlike the test for relative polarity one must know the polarity of the recordings that comprise the compilation test disc.  I know how to establish the polarity of recordings, but since I’m not ready just yet to explain how that’s accomplished the more difficult test for the ability to discern actual polarity will have to wait just a little while longer.

The standard way to scientifically compare component A against component B is by double blind ABX testing.  In order to make ABX testing a bit easier I’ve added non-X that allows the test subject to hear non-X but only knowing that it’s non-X.  When the purpose of the test is to find whether component A or B is preferred, I have a more direct protocol.  Component A and component B are played alternately double blind first one and then the other as many times as needed to state a preference.  Then the sequence is repeated with the order of A and B chosen at random for the next set of alternating comparisons.  The protocol is repeated until the results are statistically significant.  This single test will determine directly both the test subject’s ability to distinguish A from B as well as preference.

Best regards,

George, Perfect Polarity Pundit™  Copyright 2006 All rights reserved by George S. Louis

Digital Systems & Solutions
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Audibility of inverted polarity in real music

Reply #45 –
Quote from: georgelouis on
For example, simple as it may seem, a single component could degrade the sound if its power cord is plugged into the wall outlet in less than the best sounding orientation.
Can you please explain how the performance of AC power over a metallic conductor can vary with conductor direction. This claim would require some impressive proof.

Quote from: georgelouis on
Despite its many advantages it also had one major disadvantage; it wasn’t phase coherent. Without phase coherence it was impossible for me to discern polarity or to hear music purely in or out of absolute polarity because that crossover requires some of its drivers to always play in opposite relative polarities to each other.  As a result that speaker system was inconsistent with the single absolute polarity of live music.
The crossovers require you to connect some of the drivers in reverse polarity because they, themselves, reverse the phase. By connecting the drivers reversed, you restore the phase. If you didn't connect them the wrong way round, you would get a very big dip (sometimes -40dB or more) in the response in the crossover region. Crossover designers refer to this as a "reverse null" and it's depth and curves can tell you a lot about the crossover design.

Quote from: georgelouis on
3. The system’s frequency response deviates no more than  +/- 3 dB from flat between 50 and 8 kHz which is an example of an application of the rule of 400 as defined in the first edition of the Audio Cyclopedia.
+-3dB is a large amount of ripple in the pass band of your system. All the active components should be able to achieve +- 0.1dB or less over this range. Speakers are harder, but a lot of designs still do much better than this on-axis. 6dB peak-to-peak ripple in the response will likely be clearly audible as a coloration of the music or change of timbre.

Your three criteria for good sound miss out a lot of important (and audible) parameters in system design. Noise is one that you don't mention, as is total harmonic distortion (THD), intermodulation distortion (IMD) and a variety of other measurements. I think you are over-emphasising the audibility of linear effects compared to that non non-linear effects.

Quote from: georgelouis on
For example, when two tweeters are playing a 10 kHz signal, if your head is a mere 3/10ths of an inch (a quarter wavelength) closer to one tweeter than the other, the signal from one tweeter arrives at your ears 180 degrees out of phase with the signal from the other tweeter.  Although theoretically they should cancel each other perfectly, I believe most listeners will still hear the 10 kHz signal at full volume.
If the two were point sources, and you put them an integer number of wavelengths apart, then there would be places where the sound is cancelled and places where it is re-inforced. With real tweeters the picture is much, much more complex, but you will still get areas where there are peaks and areas where there are nulls.

Quote from: georgelouis on
According to "The Wood Effect" many listeners can detect the polarity of asymmetrical musical signals even though test equipment and computer programs can’t.
Computer programs certainly can, but it requires you to know a little about the signal you are dealing with. Vocal recordings, for example, often have a very assymetrical look to them, that it would be easy to identify with a computer.

Your test procedure is interesting, and it would be nice to see it implemented.

Audibility of inverted polarity in real music

Reply #46 –
as i was eletronic technician i can write:
wonderful post georgelouis,a long time i don't read clever explanations.
from the start i could feel that you have experience.[/quote]For example, simple as it may seem, a single component could degrade the sound if its power cord is plugged into the wall outlet in less than the best sounding orientation. [/quote]only experienced persons knows this details.

i don't want to quote parts from your post but some are very interesting because the users always forget /ignore important details when are doing tests(in ABX tests sometimes too).
in general i don't use statistic ABX tests as "final reference with scientific proove" because who apply the test,ignore or never knew details like the "three requirements for audio system" explained in your post to tell the minimum.
in general,how can we be sure of the "consensual scientific proove" with ignored details outside the test?
nothing against the tests but they are incomplete!

i'm sad because i can't write in plain english like you but i can read and understand.
have more people that knows what he only read somewhere that people that knows what he learn and have experience.(here you can read my crap english)

welcome and best regards.

Audibility of inverted polarity in real music

Reply #47 –
ABX procedures or tools are used by people at home to test audibility of differences with their own equipment, an in this context they are perfectly valid. They are "personal" tests. Often, people with very good equipment don't get very different results.

Professional researchers, on the contrary, use reference level equipment for their double-blind tests, be in the form of ABX, ABC/HR or other variant.

Audibility of inverted polarity in real music

Reply #48 –
Quote from: KikeG on
ABX procedures or tools are used by people at home to test audibility of differences with their own equipment, an in this context they are perfectly valid. They are "personal" tests. Often, people with very good equipment don't get very different results.

Professional researchers, on the contrary, use reference level equipment for their double-blind tests, be in the form of ABX, ABC/HR or other variant.

i agree with you, you wrote clever but the same as me.
(now i'm trying to explain)...
i wrote that "in general i don't use statistic ABX tests as "final reference with scientific proove" because who apply the test,ignore or never knew details like ...
means:
"in general" =don't means that i don't use.
"final reference with scientific proove" = general consensus. some people(lots here) knows how to use,others are sure that knows but commit mistakes.
"statistic" and  "who apply the test" = results from group of persons doing tests but ignore or...etc.
(i told,crap english here)

ABX,ABC/HR are perfects only for who knows what is doing...
no one knows ABX better than you and i'm right that you know what i mean now.

...and forgive my english!
regards.

Audibility of inverted polarity in real music

Reply #49 –
Finally! George found my thread. I was wondering when you'd get around to it.

I don't have a whole lot of time right now to reply to all of that (I ought to have been in bed an hour ago). But I will say that, if I had to do the polarity test again, except with 1-minute tracks to compare blindly, I believe I would have absolutely failed. I had to change tracks much, much faster than that to get any sort of consistency. I don't think I could have done it without computer-aided ABX testing, and foobar in particular. (Then again, I don't consider myself a particularly detailed listener. I fail ABXing of 128kbps encodes on a regular basis.)

I usually zeroed in on a roughly 5-second section of the music and listened to each version repeatedly, as fast as possible, but occasionally I listened to a selection roughly half a second long and alternated between the two half-second tracks as fast as possible.

The scientific literature I'm aware of (but alas can't quote off the top of my head) says that audio memory is strongest in the last few seconds, and you really start to forget things after a minute. They're not kidding. That completely supports my experience.