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Audibility of inverted polarity in real music

There were some questions a while ago as to if inverting the polarity of a signal was audible.  After some discussionon head-fi, gaboo successfully ABX'd a polarity inversion. So far I'm completely unable to ABX his sample, but after poking around with another sample I was able to ABX a polarity inversion 10/10 in foobar.

Setup was as follows:
- Sound system was Chaintech AV-710 in high sampling 2-ch mode wired to Etymotics ER-4S phones
- Source material was 0:06-0:13 of Primus's "Hamburger Train" from "Pork Soda" (WAV ripped in iTunes)
- Inversion was performed with foo_invert, a plugin of my own devising. PM me for source if you want it. I verified its correct operation by doing a "quick mix" of the original and inverted WAVs in Audacity and verified the resultant file had all-zero samples.
- ABX testing was performed with only Volume Control in the plugin chain, 32 bit output, no dithering, 44.1khz.
- I did the ABX on the original 8:11 WAVs but only uploaded the 0:06-0:13 clip, so the filenames don't match the ABX result text. Hope that doesn't ruffle any feathers.

foo_abx v1.2 report
foobar2000 v0.8.3
2004/10/25 13:35:51

File A: file://C:\m\13 Hamburger Train.wav
File B: file://C:\m\13 Hamburger Train b.wav

13:36:17 : Test started.
13:38:44 : 01/01  50.0%
13:46:02 : 02/02  25.0%
13:46:57 : 03/03  12.5%
13:47:16 : 04/04  6.3%
13:48:11 : 05/05  3.1%
13:48:27 : 06/06  1.6%
13:48:42 : 07/07  0.8%
13:49:29 : 08/08  0.4%
13:49:46 : 09/09  0.2%
13:50:35 : 10/10  0.1%
13:50:39 : Test finished.

----------
Total: 10/10 (0.1%)

EDIT: What's the actual difference, you ask? It's best described as a very faint change in timbre in high-intensity percussives. It sort of sounds like a change in pitch, but I've found that's not really the best way to go about listening for it. Others have commented that low-frequency drum kicks seem to be sounding like they're coming from the opposite direction, but Etys are definitely not the phones to be listening for that sort of thing. This definitely was at the very cusp of my listening ability, but this 10/10 was on the very first time I tried testing with this clip.

Samples and plugin here.

Audibility of inverted polarity in real music

Reply #1
Man, no offence, that hamburger hill stuff is horrible, can't get myself to listen to it even a few of times, let alone do an ABX.
The earth is round (P < 0.05).  -- Cohen J., 1994

Audibility of inverted polarity in real music

Reply #2
Quote
Man, no offence, that hamburger hill stuff is horrible, can't get myself to listen to it even a few of times, let alone do an ABX.
[a href="index.php?act=findpost&pid=250215"][{POST_SNAPBACK}][/a]

Aw, c'mon! Face it, if you're already ABXing this sort of thing, you already like pain  I probably ought to have done fade in/out on those clips too..

I tried ABXing again last night on my home system (RME PAD, Gilmore v2 amp, and either ATH-A900s or Etys) and I failed miserably through 16 or so trials. Then I did it again today from work in a couple minutes (AV-710 system) and got 8/8 on the first attempt. Go figure. So so far I have never missed a blind test with hamburger_train on my work system, but have always failed all tests on my home system. I'm starting to wonder if either there's something wrong with my work system, some sort of distortion that makes the reversal more audible, or something wrong with my home system that masks it. Or, my hearing may just be significantly degraded between the early afternoon and the late evening to the point that I can't hear it. I'll definitely need to look into this some more.

Audibility of inverted polarity in real music

Reply #3
There are physiological reasons that can support audibility of inverted polarity, but there are restrictions to the scope.
It has been found that ear is sensitive to positive pressure, negative pressure being ignored. This leads to expectation that if signal is asymmetric wrt zero, it can become audible when inverting polarity.
If the signal is symmetric, no audibility is justified. Some instruments are known to produce asymmetric signal, so it depends on content.
It really really did sound different. Not in a placebo way.

Audibility of inverted polarity in real music

Reply #4
Quote
There are physiological reasons that can support audibility of inverted polarity, but there are restrictions to the scope.
It has been found that ear is sensitive to positive pressure, negative pressure being ignored. This leads to expectation that if signal is asymmetric wrt zero, it can become audible when inverting polarity.
If the signal is symmetric, no audibility is justified. Some instruments are known to produce asymmetric signal, so it depends on content.
[a href="index.php?act=findpost&pid=250388"][{POST_SNAPBACK}][/a]

I'm well aware of the physiological reasons for audibility, especially the rectification effect of the cilia. I don't think the signal needs to be asymmetric - the Wood effect was demonstrated by just tweaking the duty cycle of a sine wave, so that the last several degrees were zeroed out - which didn't affect the amplitude symmetry at all. But if the rising wave of the transient is of a much different amplitude than the falling wave then I could definitely see that as being a good candidate for audibility. And of course very loud bass kicks have periods so large that they ought to be good candidates too.

Moreover, my understanding of the literature is that so far it has only been experimentally detected under very strict listening conditions, very rarely with real CDs (much less Primus and consumer gear), and never on HA. Past discussions on the subject have not yielded a concrete conclusion, since nobody had really successfully ABX'd it.

(not that I'm quite claiming victory just yet. Once again I failed to ABX it at home, 4/12. Granted, I had alcohol in my system, and it was some ungodly hour of the night, so those are very extenuating circumstances, but still...)

Mods, is this the best forum for the thread? I was expecting a lot more discussion on this, given the 16/24 discussion...

Audibility of inverted polarity in real music

Reply #5
OK, after a successful test tonight, I can more or less declare this as a fact: I can ABX hamburger_train, on the AV710, with the Etys. I cannot ABX it with the Etys and my RME/Gilmore combo. I cannot ABX it with my A900s and the RME/Gilmore combo. I haven't tried A900s and the AV-710 yet.

Tested to a multiple of 8 on the AV710, tested just now, in my usually fatigued state in the middle of the night:

foo_abx v1.2 report
foobar2000 v0.8.3
2004/10/28 01:54:04

File A: file://C:\hamburger train.flac
File B: file://C:\hamburger train inverted.flac

01:54:04 : Test started.
01:54:44 : 01/01  50.0%
01:54:51 : 02/02  25.0%
01:55:09 : 03/03  12.5%
01:55:16 : 04/04  6.3%
01:55:39 : 05/05  3.1%
01:56:04 : 05/06  10.9%
01:56:18 : 06/07  6.3%
01:56:24 : 06/08  14.5%
01:56:31 : 07/09  9.0%
01:56:37 : 07/10  17.2%
01:56:47 : 07/11  27.4%
01:57:03 : 08/12  19.4%
01:57:49 : 09/13  13.3%
01:58:25 : 10/14  9.0%
01:59:11 : 11/15  5.9%
01:59:25 : 12/16  3.8%
01:59:35 : 13/17  2.5%
01:59:41 : 14/18  1.5%
01:59:48 : 15/19  1.0%
02:00:03 : 16/20  0.6%
02:00:15 : 17/21  0.4%
02:00:21 : 18/22  0.2%
02:00:28 : 19/23  0.1%
02:00:37 : 19/24  0.3%
02:00:45 : Test finished.

----------
Total: 19/24 (0.3%)

And, as usual, utter failure on the RME, something like 4/8 right before the above test. It's not like I can tell any obvious distortion with the RME, like it's obviously messing up or anything like that - it's like the difference is just not there. This may not be an indictment of the RME, as it's quite conceivable that the AV710 is distorting in such a way that the reversal can become audible when it really shouldn't be. If so, then this really doesn't strengthen anybody's argument for audibility.

So, active hypotheses which I'll need to work on:
- RME is distorting and AV710 isn't, leading to masked polarity effect. To test: Find another ABX test which, if positive, virtually certainly indicates a difference due to the signal itself and not distortion; pass the test with the AV710 and fail it with the RME. Start with high frequency equalization testing. Alternatively, quantify any distortion present on the RME from the AV710 and write a plugin that replicates it; verify that the processed wavs cannot be ABX'd.
- Gilmore is distorting and AV710 isn't. To test: hook up Gilmore to AV710 and redo.
- AV710 is distorting and RME isn't, leading to nonlinear distortion with inverted polarity. To test: If the ABX fails with the AV710 running amped (with the Gilmore) then the issue gets rearranged into "is the Gilmore distorting?" and goto above.
- Both RME and AV710 are distorting but in different ways. This isn't really testable with current equipment.
- I'm trying harder on AV710 testing than on RME testing. Believe me, I'm not.
- Processing errors. I'm confident these did not occur and others can verify this with the uploaded flacs.

BTW, anybody's help with ABXing these or gaboo's samples are greatly appreciated.

Audibility of inverted polarity in real music

Reply #6
I tested tonight with the AV-710, the Gilmore and the ER-4S. Test started off to 16, but due to my inordinate failure to get a positive result I decided to extend the test and try harder. I was convinced I wasn't just waiting for a positive result to come along due to chance at 25/34.

foo_abx v1.2 report
foobar2000 v0.8.3
2004/10/29 01:05:41

File A: file://C:\hamburger train.flac
File B: file://C:\hamburger train inverted.flac

01:05:41 : Test started.
01:06:10 : 01/01  50.0%
01:06:17 : 02/02  25.0%
01:06:27 : 03/03  12.5%
01:06:49 : 03/04  31.3%
01:07:21 : 04/05  18.8%
01:07:28 : 05/06  10.9%
01:07:35 : 05/07  22.7%
01:07:53 : 06/08  14.5%
01:08:04 : 06/09  25.4%
01:08:39 : 07/10  17.2%
01:08:56 : 07/11  27.4%
01:10:57 : 08/12  19.4%
01:11:05 : 09/13  13.3%
01:11:17 : 10/14  9.0%
01:11:29 : 10/15  15.1%
01:12:30 : 11/16  10.5%
01:12:39 : 12/17  7.2%
01:12:58 : 12/18  11.9%
01:13:12 : 13/19  8.4%
01:13:39 : 14/20  5.8%
01:13:47 : 15/21  3.9%
01:14:04 : 16/22  2.6%
01:14:19 : 17/23  1.7%
01:14:57 : 18/24  1.1%
01:15:14 : 19/25  0.7%
01:15:23 : 19/26  1.4%
01:15:31 : 20/27  1.0%
01:15:52 : 21/28  0.6%
01:15:59 : 22/29  0.4%
01:16:07 : 23/30  0.3%
01:16:25 : 23/31  0.5%
01:16:38 : 23/32  1.0%
01:16:57 : 24/33  0.7%
01:17:36 : 25/34  0.5%
01:17:57 : Test finished.

----------
Total: 25/34 (0.5%)

So I am able to ABX with the amp; the odd man out here is the RME. I assert this immediately eliminates the Gilmore or the output stage of the 710 as being likely sources of distortion. (One thing I failed to mention earlier is that I was using the 710 in high-sampling-rate mode, on the rear speaker outputs, but I was NOT resampling to 96khz during the ABX.) This leaves either the RME DAC or the 710 DAC.

As a quick test to make sure the test wasn't corrupted by playing the tracks at 44.1 instead of 96 as suggested by the drivers, I did a quick test at 96 using SSRC:

foo_abx v1.2 report
foobar2000 v0.8.3
2004/10/29 01:33:41

File A: file://C:\hamburger train.flac
File B: file://C:\hamburger train inverted.flac

01:33:43 : Test started.
01:34:55 : 01/01  50.0%
01:35:13 : 02/02  25.0%
01:35:18 : 03/03  12.5%
01:35:25 : 04/04  6.3%
01:35:46 : 04/05  18.8%
01:35:52 : 05/06  10.9%
01:36:02 : 06/07  6.3%
01:36:07 : 07/08  3.5%
01:36:12 : Test finished.

----------
Total: 7/8 (3.5%)

To determine which of the two could be at fault, I propose one "easy" test and one "hard" tests. The first "easy" test is to implement a polarity test that is known to pass on any reasonable hardware, using artificial signals. I'll first try the Wood effect (clipped sine waves) and pulses of opposite polarity. The "hard" test is to locate a suitably precise data acquisition card, put both cards under the knife, and try and numerically identify a distortion effect which could result in the observed results.

Audibility of inverted polarity in real music

Reply #7
Advice:  You're going to need to produce better than 7/8 results.


Note: Not criticism, just advice

Audibility of inverted polarity in real music

Reply #8
Just a note on ABX testing:  the number of total trials should be decided on before starting the test.  Initially deciding on 16, and then monitoring the results until you get a desirable endpoint is a form of "cherry picking."

If you're interested in ABXing a small effect, and don't want to err by saying "there's no difference" when in fact there is one, you need to be prepared to perform a lot of trials.

This beta version of abchr has a training abx mode, will hide the in-progress results for a real test, and calculates required trials to get desired error risks given the size of the effect.

http://ff123.net/export/abchr1.1beta2.zip

ff123

Audibility of inverted polarity in real music

Reply #9
OK, from now on I'll fix the number of trials at 32 for all tests. I'm fairly confident I can ABX consistently at that N.

Audibility of inverted polarity in real music

Reply #10
Basically ABX is a scientific tool/statistical tool which enables you to prove that there is a statistical difference between two different audio files.  This requires quite a few attempts and successes to be statistically sound.  The assumption is made before the test that the two files will not produce an audible difference but when a certain confidence level is reached either .1 or .01 as a result of a number of successful trials, only then can two files be scientifically/statistically proven different in their sound.

Audibility of inverted polarity in real music

Reply #11
Quote
Basically ABX is a scientific tool/statistical tool which enables you to prove that there is a statistical difference between two different audio files.  This requires quite a few attempts and successes to be statistically sound.  The assumption is made before the test that the two files will not produce an audible difference but when a certain confidence level is reached either .1 or .01 as a result of a number of successful trials, only then can two files be scientifically/statistically proven different in their sound.
[a href="index.php?act=findpost&pid=250853"][{POST_SNAPBACK}][/a]

GUys, I don't need a lecture on blind testing, I know exactly what's involved. First of all, in the context of most listening tests conducted on this site, my understanding is that a confidence level of 0.05 is considered acceptable, and I'm clocking in waaaaay under that - <0.005, to be exact. And I do understand how cherry-picking the stopping point for the test can reduce the significance of the results.

But how can my results be weakened beyond significance if the significance I'm already at is very strong? ie, it's idiotic to throw out a positive test where the stopping point was cherry-picked at N>100 and p<0.001 - at what point does the stopping point matter? Moreover, if I was cherry picking the place to stop, wouldn't some tests necessarily need to be conducted an indefinite number of times due to chance?

My only confusion appears to be in the nature of defining the number of trials, and even then I don't think my current results are significantly weakened. I will admit to a very slight bit of cherry picking on the 25/34: I missed one trial, exited, checked my config (and didn't wind up changing anything). IIRC every other test was from the first trial on.

In any case: this is no longer an active issue, I'll make sure the tests I do in the future are N=32.

Audibility of inverted polarity in real music

Reply #12
OK, I've had time to do N=32 tests on both cards, and finally, I can kinda-sorta claim positive ABX results on the RME. Configuration: volume levels set to whatever I felt was appropriate to do testing and were allowed to be changed mid-test. Card was routed through RS Gold 1/8-RCA stereo cable to Gilmore V2, then on to ER-4S phones. RME was set to -6dB and AV-710 was set to full volume. ABX was done through foobar with SSRC resampler at 96khz and no other DSP components. Absolutely no tests were dropped and no training was done before the tests.

The AV-710 test was done first:

foo_abx v1.2 report
foobar2000 v0.8.3
2004/10/31 19:12:14

File A: file://C:\hamburger train.flac
File B: file://C:\hamburger train inverted.flac

19:12:16 : Test started.
19:13:18 : 00/01  100.0%
19:13:55 : 01/02  75.0%
19:14:20 : 02/03  50.0%
19:14:29 : 02/04  68.8%
19:14:48 : 03/05  50.0%
19:14:56 : 04/06  34.4%
19:16:31 : 05/07  22.7%
19:17:05 : 06/08  14.5%
19:17:29 : 07/09  9.0%
19:17:40 : 08/10  5.5%
19:18:15 : 09/11  3.3%
19:18:31 : 10/12  1.9%
19:18:48 : 10/13  4.6%
19:20:40 : 11/14  2.9%
19:21:03 : 12/15  1.8%
19:21:19 : 13/16  1.1%
19:21:32 : 14/17  0.6%
19:23:30 : 15/18  0.4%
19:23:42 : 16/19  0.2%
19:24:07 : 16/20  0.6%
19:24:31 : 17/21  0.4%
19:24:39 : 18/22  0.2%
19:25:09 : 19/23  0.1%
19:25:17 : 20/24  0.1%
19:25:40 : 21/25  0.0%
19:25:47 : 22/26  0.0%
19:26:15 : 23/27  0.0%
19:26:23 : 24/28  0.0%
19:26:31 : 25/29  0.0%
19:26:39 : 26/30  0.0%
19:26:48 : 26/31  0.0%
19:27:07 : 26/32  0.0%
19:27:14 : Test finished.

----------
Total: 26/32 (0.0%)

No surprise here. Next the RME:

foo_abx v1.2 report
foobar2000 v0.8.3
2004/10/31 20:03:04

File A: file://C:\hamburger train.flac
File B: file://C:\hamburger train inverted.flac

20:03:05 : Test started.
20:04:47 : 01/01  50.0%
20:05:06 : 01/02  75.0%
21:06:53 : 02/03  50.0%
21:07:00 : 03/04  31.3%
21:07:27 : 03/05  50.0%
21:08:19 : 04/06  34.4%
21:08:27 : 05/07  22.7%
21:08:38 : 05/08  36.3%
21:08:58 : 06/09  25.4%
21:09:09 : 07/10  17.2%
21:09:32 : 07/11  27.4%
21:10:06 : 08/12  19.4%
21:10:17 : 08/13  29.1%
21:10:29 : 09/14  21.2%
21:10:59 : 10/15  15.1%
21:11:11 : 10/16  22.7%
21:11:42 : 11/17  16.6%
21:11:50 : 12/18  11.9%
21:11:57 : 13/19  8.4%
21:12:13 : 13/20  13.2%
21:12:40 : 14/21  9.5%
21:12:59 : 15/22  6.7%
21:13:11 : 15/23  10.5%
21:13:26 : 16/24  7.6%
21:13:34 : 17/25  5.4%
21:13:41 : 18/26  3.8%
21:13:53 : 19/27  2.6%
21:14:04 : 19/28  4.4%
21:14:15 : 20/29  3.1%
21:14:27 : 21/30  2.1%
21:14:42 : 22/31  1.5%
21:14:54 : 23/32  1.0%
21:14:56 : Test finished.

----------
Total: 23/32 (1.0%)

Finally, a halfway-positive ABX result on this card (p<0.01). The primary artifact I've been listening for on the Chaintech has been a raise in timbre/pitch on the inverted sample on the drump strike at the theme transition, about 3.5 seconds in. This is next to impossible to hear on the RME. Eventually I figured out another effect, a sort of increase in air/loss of dynamic range between the drum hits, which contributed one or two points to the final score when I couldn't figure out X/Y from the drum strikes alone.

I can't help but agree with the subjective opinions at Head-Fi that there is a general muddiness in the high end on this card, because overall the sound felt a bit more "toppy" than the AV-710, and not in a good way. Nevertheless the difference between the Chaintech and the RME is very, very hard to spot, and I don't think I could notice it in a nonblind test.

Nevertheless, the 3 points less result on the RME belied the fact that I had a much harder time with the test than on the Chaintech. With the Chaintech, I could often reach a firm conclusion after listening to the sample for less than a second, and when I didn't, it was usually because I either got the last round wrong or I (rarely) missed the timbre change and needed some more time. With the RME, every test was a long struggle. I hope this is enough of a reassurance to assuage my own complaints about this sort of blind test, but again, you basically need to take me on faith that I tested both cards equally hard.

About the only thing left I'd like to do is make sure this is audible on my A900's. Then I'm claiming victory. I don't think it's necessary at this point to delve into objective testing between the sounds of the RME and the AV-710; everybody here seems to be OK with subjective descriptions between encoder samples on positive ABX results, so I think it's reasonable to give subjective descriptions on negative (or close to negative) ABX results.

Audibility of inverted polarity in real music

Reply #13
Tests for Audio Technica ATH-A900, Chaintech AV-710, everything else same as last post.

foo_abx v1.2 report
foobar2000 v0.8.3
2004/10/31 21:56:40

File A: file://C:\hamburger train.flac
File B: file://C:\hamburger train inverted.flac

21:56:42 : Test started.
21:57:18 : 01/01  50.0%
21:57:25 : 01/02  75.0%
21:57:33 : 01/03  87.5%
21:58:14 : 02/04  68.8%
21:58:34 : 03/05  50.0%
21:58:45 : 04/06  34.4%
21:59:38 : 05/07  22.7%
21:59:54 : 06/08  14.5%
22:00:07 : 06/09  25.4%
22:01:10 : 07/10  17.2%
22:01:26 : 08/11  11.3%
22:02:23 : 09/12  7.3%
22:02:31 : 10/13  4.6%
22:02:44 : 10/14  9.0%
22:04:20 : 10/15  15.1%
22:04:52 : 11/16  10.5%
22:05:00 : 11/17  16.6%
22:05:17 : 12/18  11.9%
22:06:18 : 12/19  18.0%
22:06:35 : 13/20  13.2%
22:06:51 : 14/21  9.5%
22:06:59 : 15/22  6.7%
22:07:07 : 16/23  4.7%
22:07:40 : 17/24  3.2%
22:07:47 : 18/25  2.2%
22:07:59 : 19/26  1.4%
22:08:10 : 19/27  2.6%
22:08:30 : 19/28  4.4%
22:09:15 : 20/29  3.1%
22:09:47 : 20/30  4.9%
22:10:16 : 20/31  7.5%
22:10:24 : 21/32  5.5%
22:10:26 : Test finished.

----------
Total: 21/32 (5.5%)

Grumble. Important results, but not significant enough. The change in timbre was not nearly as noticable as even on the RME with the ER-4S, and I had to instead rely on more intangible quantities like "air".

What do you guys think? Are my results significant enough as they stand? What else would you like tested that would be reasonable for me to test?

Audibility of inverted polarity in real music

Reply #14
I believe most power amplifier cascades actually have two parts -- one transistor amplifying the upper half-wave, another one amplifying the lower half -- one being p-n-p, the other one n-p-n. Because it's fairly difficult to manufacture two semiconductors on a different base with exactly the same amplification slopes, it's very possible to have lower half of your signal amplified slightly more than the upper half, or vice versa -- thus making even a perfectly symmetric signal asymmetric.

Even if you have just one regular transistor amplifying your signal (pre-amp cascade), the output can still be asymmetric if the bias current is not tuned perfectly -- and besides, even in the vicinity of the bias current, the amplification curve of a transistor is not exactly a straight line, nor is it perfectly symmetric about the bias current.

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.

This would explain why your ABX is so much dependent on the equipment you are using -- with this sort of thing, you are essentially testing your equipment as much (if not more) as your hearing.

Audibility of inverted polarity in real music

Reply #15
Quote
Because it's fairly difficult to manufacture two semiconductors on a different base with exactly the same amplification slopes, it's very possible to have lower half of your signal amplified slightly more than the upper half, or vice versa -- thus making even a perfectly symmetric signal asymmetric.

You are completely wrong. You would have first a basic knowledge in electronics before giving an opinion about topics that you don't know well.

Today the audio amplifiers don't suffer of this problem, because the negative feedback compensates all these nonlinearities; with this you obtain a perfect symmetric output signal; with levels of THD (total harmonic distortion) so low that they are only noticeable with measuring instruments.

Quote
Even if you have just one regular transistor amplifying your signal (pre-amp cascade), the output can still be asymmetric if the bias current is not tuned perfectly -- and besides, even in the vicinity of the bias current, the amplification curve of a transistor is not exactly a straight line, nor is it perfectly symmetric about the bias current.

The modern audio circuits are composed by many transistors, not only one, and the bias is tuned correctly; and, in the majority of the cases (in low level signals) this is done with operational amplifiers composed with a lot of transistors with correct bias. Even in the case of final power amplifiers stages (clase AB) the effect the crossover distortion is completely nonexistent, as a result of a good combination of adequate bias current and negative feedback; all these are basic factors of design taken in consideration in today electronics.

Quote
This would explain why your ABX is so much dependent on the equipment you are using -- with this sort of thing, you are essentially testing your equipment as much (if not more) as your hearing.

Wrong. Your arguments don't have sense at all. The cause is not the audio equipment.

Audibility of inverted polarity in real music

Reply #16
Quote
You are completely wrong. You would have first a basic knowledge in electronics before giving an opinion about topics that you don't know well.

I do have more than a basic knowledge in electronics, although my knowledge may be out of date, so save your breath; explaining where I was wrong here is sufficient.

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Today the audio amplifiers don't suffer of this problem, because the negative feedback compensates all these nonlinearities; with this you obtain a perfect symmetric output signal; with levels of THD (total harmonic distortion) so low that they are only noticeable with measuring instruments.

The modern audio circuits are composed by many transistors, not only one, and the bias is tuned correctly; and, in the majority of the cases (in low level signals) this is done with operational amplifiers composed with a lot of transistors with correct bias. Even in the case of final power amplifiers stages (clase AB) the effect the crossover distortion is completely nonexistent, as a result of a good combination of adequate bias current and negative feedback; all these are basic factors of design taken in consideration in today electronics.

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.

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Wrong. Your arguments don't have sense at all. The cause is not the audio equipment.

You still have not answered the headphone/speaker part. Care to exercise your basic knowledge in physics?

Audibility of inverted polarity in real music

Reply #17
Why did you put the AV-710 in high sampling mode for a 44.1 kHz track?

Audibility of inverted polarity in real music

Reply #18
Higher 'quality'.  Just kidding. Perhaps there is a valid reason.
Acid8000 aka. PhilDEE

Audibility of inverted polarity in real music

Reply #19
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Higher 'quality'.  Just kidding. Perhaps there is a valid reason.
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I know that the guides say to use HS mode to get output through channels 7&8, which are attached to the WM DAC, but the new drivers allow 7&8 output in regular 2 channel mode (see Wish's post [a href="http://www.hydrogenaudio.org/forums/index.php?showtopic=34940]here[/url]). Using 2 channel mode would rule out the possibility of some sort of resampling quirk causing the difference.

Axon: As only Volume Control was in the DSP chain I'm assuming you let kMixer handle the resampling?

Audibility of inverted polarity in real music

Reply #20
If you guys look at the last time axon posted, it was october last year! While i'm sure he's still around, that would explain why his tests were done in "high rez" mode because like you said, the driver's that do 16/44.1 on the wolfson dac probably didnt exist then.

Last night i re-read through this thread. Then this mornining with a clear head, i did some ABX testing on my speakers.

My setup is e-mu 0404 > tripath amplifier > klipsch bookshelf speakers. I was easily able to hear what Axon described as a change in timbre.

I used the e-mu's phase invert which is just a button you press "on/off" and it changes the phase/polarity on the fly gaplessly. This is assuming e-mu's phase invert does the same thing as switching polairty 180 degrees.

Although I didnt ABX myself because i could see if the phase switch was on or off when i clicked it. It really really did sound different. Not in a placebo way. Since I can't prove it till I try out Axon's fb2k plugin, try and take my word for it too, the difference is there. If you have an e-mu card try it out for yourself.

-Joe

Audibility of inverted polarity in real music

Reply #21
You guys are testing your equipment!
It really really did sound different. Not in a placebo way.

Audibility of inverted polarity in real music

Reply #22
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You guys are testing your equipment!
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Damn straight!  reversing polarity has much more darastic effects on headphones vs speakers.

2-driver loudspeakers tend to have crossovers where the tweeters are 90degrees off one axis and the woofer 90degrees the other way. So when reversing polarity, your really only reversing the polarity of your tweeter in conjunction with the woofer.

Headphones are a whole different deal, you can lump in headphones with full range drivers for loudspeakers because they use one driver to handle the whole "range". It might not be obvious with a straight up tone, but once you start introducing multiple tones you get "doppler distortion" and once this happens you notice polarity really quickly, that's why full range drivers tend to have lots of frequency modulation distortion.

Here's an example to help see what i'm talking about. If you have a kick drum and a flute duet. The kick drum moves the air forward while the flute rides on top of it. Now if you reverse the signal the driver moves backwards while playing the very same flue signal. But since sound's frequency increases as it moves twoard the listener and decreases as it goes away (think a train passing you) you basically end up changing the hanging pitch of the flute when you do this with full range drivers because the cone motion is so drastically different beween the kick drum and flute frequencies.

Speaker users will notice this, an interesting concept is that we don't just listen to sound with our ears...we feel it in our chest too. If you get the polarity backwards on a kick drum it starts to sound wierd because you're expecting a compression wave to hit you first, not a trough followed by a smaller compression. Put your hand in front of the speaker and feel the air move by when the kick hits...then reverse the polarity and notice how much it changes. You practically don't feel it when the woofer moves away from you at first.

Btw, it doesn't matter if absolute polarity was maintained throughout the entire signal chain (studio/mastering facility etc etc) because the relative polarity of everything in the mix will be the same throughout the chain. It's then up to the listener to determine when the polarity should be switched, but I can't think of any recordings that I own though that might require this.

Audibility of inverted polarity in real music

Reply #23
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.)

Anyways, given the failure of most/all ABX tests against amplifiers, compared to the very well known and documented Wood Effect, I would much more easily believe that the reversal is audible than believe a problem with my system. I could be persuaded otherwise.

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Why did you put the AV-710 in high sampling mode for a 44.1 kHz track?

The Wolfson DACs on the rear outs are considered objectively superior to those on the front stereo channels.

Actually I think that my card could accept 44.1. And I'm 99% sure I avoided kMixer on this chain, because the rear output mode doesn't even accept mono signals as an input - you need to convert to stereo explicitly. If kMixer were there it should have been able to convert automatically.

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Headphones are a whole different deal, you can lump in headphones with full range drivers for loudspeakers because they use one driver to handle the whole "range". It might not be obvious with a straight up tone, but once you start introducing multiple tones you get "doppler distortion" and once this happens you notice polarity really quickly, that's why full range drivers tend to have lots of frequency modulation distortion.

Doppler distortion only applies to loudspeakers because it's supposed to be correlated to the velocity of the driver, and extremely long displacements are necessary to pull it off. So far, not only has it not been ABX'd AFAIK, I'm not even sure Stereophile believes it's audible.

Audibility of inverted polarity in real music

Reply #24
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The Wolfson DACs on the rear outs are considered objectively superior to those on the front stereo channels.
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I certainly agree the WM DAC is far superior. I'm playing 44.1 kHz music in normal 2 channel mode through the rear outs using the latest Via drivers and foobar2000 in KS mode. Electrically the Via DACs are not connected to the rear outs.

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Actually I think that my card could accept 44.1. And I'm 99% sure I avoided kMixer on this chain, because the rear output mode doesn't even accept mono signals as an input - you need to convert to stereo explicitly. If kMixer were there it should have been able to convert automatically.

The card can accept 44.1, that's my point, but only in normal 2 channel mode. By setting it to high sample rate mode you are restricting it to >96 kHz. Try playing a 44.1 sound file in foobar2000 using KS in high resolution mode - it will give you a KS output error, because the card will only accept >96 kHz audio in high sample rate mode.

The reason you can play back 44.1 in high sample rate mode through DS or waveOut is kMixer is resampling the audio to 96 kHz. The card can not accept anything less in high sample rate mode through any output method.

Try putting it in normal 2 channel mode, then use KS in foobar2000 to feed it 44.1 kHz sound, it should play correctly through the rear output. If not, try grabbing the latest Via drivers, because it's working fine for me.

 
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