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High-order dither listening test
High-order dither listening test
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Old 15th November 2017, 08:51 PM   #71
MarcelvdG is offline MarcelvdG  Netherlands
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Hi PMA and Mooly,

Today I suddenly realized that there might be a fatal flaw in the tests done so far. If you can hear a difference between two realizations of the same stochastic process, then all tests done so far are meaningless. For example, if you have two recordings of additive noise with the same probability distribution, do they necessarily sound exactly the same or can they sound slightly different because noise by definition has random variations?

The only way I can think of to exclude this effect from affecting the experiment is this:

-I make one file with additive noise that is marked as having additive noise
-I make one file with dither and requantization that is marked as being requantized
-I make ten files marked X1...X10 or so with either additive noise or dither and requantization, depending on the flip of a coin, and keep a secret list of what is what. (The files have to have the same format to get equal file sizes and bit rates.)
-You listen to it, try to categorize the files as additive noise / dithered and requantized and send the result to me by PM

I could do this for the drum music with 12 bits for PMA and with "I do like to be beside the seaside" and 8 bits for Mooly, if you are prepared to do this experiment.

Regards,
Marcel
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Old 16th November 2017, 01:37 PM   #72
Mooly is offline Mooly  United Kingdom
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High-order dither listening test
Ten ! Ten files I hope there is a good prize on offer

I suspect the idea of ten such files fills Pavel with as much horror as it does me

To my way of thinking it would only be feasible if there was a long time period to play around with them, perhaps just trying one or two a day at most. It would be to much of a chore otherwise, even if it is gratifying to get a positive result at the end... if that makes sense.
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Old 16th November 2017, 08:54 PM   #73
MarcelvdG is offline MarcelvdG  Netherlands
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You could take as long as you like, of course, but the amount of work would be similar to the ABX tests you've already done. The difference is that you don't need the ABX plugin now. You simply have files marked X1 to X10 and have to listen whether they sound more similar to file A (additive noise) or to file B (dithered quantization).
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Old 27th November 2017, 10:11 PM   #74
MarcelvdG is offline MarcelvdG  Netherlands
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I finally made the 8 bits files and files with matching additive noise. If you are still prepared to do the test, you can download them here:

WeTransfer

and PM me to tell me which of the X files have noise that sounds like additive noise and which have requantization.
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Old 28th November 2017, 05:39 PM   #75
Mooly is offline Mooly  United Kingdom
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High-order dither listening test
It seems rude not to

I'll pm you shortly with my findings. I didn't use an ABX routine but just listened to each. I wonder if the concentration wavers because I had 3 attempts and all were similar for the first 6 or so... and so I had a final attempt.
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Old 29th November 2017, 07:25 AM   #76
Mooly is offline Mooly  United Kingdom
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High-order dither listening test
I have just tried an ABX with the two master files and seem to be able to get a reliable result.

For anyone following this I flunked the identification of the 10 random files getting just 4 out of 10 correct. I didn't ABX those but tried to rely on audible memory. Interesting

Code:
foo_abx 2.0.4 report
foobar2000 v1.3.16
2017-11-29 08:12:55

File A: silverysea8bits.wav
SHA1: a0046ce776698edb27e49beaf4ca8951e175adb8
File B: silveryseaaddednoise.wav
SHA1: 901a09aa1c3a66f333ec1930536213c1c98975fe

Output:
DS : Primary Sound Driver
Crossfading: NO

08:12:55 : Test started.
08:13:21 : 01/01
08:13:30 : 02/02
08:13:42 : 03/03
08:13:57 : 03/04
08:14:06 : 04/05
08:14:23 : 05/06
08:14:37 : 06/07
08:14:52 : 07/08
08:14:52 : Test finished.

 ---------- 
Total: 7/8
Probability that you were guessing: 3.5%

 -- signature -- 
8ef7b547476e3e21e79e1004b151b508f1cbc793
Code:
foo_abx 2.0.4 report
foobar2000 v1.3.16
2017-11-29 08:20:23

File A: silverysea8bits.wav
SHA1: a0046ce776698edb27e49beaf4ca8951e175adb8
File B: silveryseaaddednoise.wav
SHA1: 901a09aa1c3a66f333ec1930536213c1c98975fe

Output:
DS : Primary Sound Driver
Crossfading: NO

08:20:23 : Test started.
08:20:43 : 01/01
08:21:10 : 02/02
08:21:25 : 03/03
08:21:36 : 04/04
08:21:46 : 05/05
08:21:58 : 06/06
08:22:23 : 06/07
08:22:32 : 07/08
08:22:32 : Test finished.

 ---------- 
Total: 7/8
Probability that you were guessing: 3.5%

 -- signature -- 
7565797d24b61bfcca856eb7a6431ceb753a0e0c
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Old 29th November 2017, 08:38 PM   #77
MarcelvdG is offline MarcelvdG  Netherlands
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I suspect that when you ABX test two of the files with added noise (two realizations of the same stochastic process), you will also be able to hear the difference. The same holds for ABX testing two of the 8 bit files.
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Old 29th November 2017, 09:40 PM   #78
MarcelvdG is offline MarcelvdG  Netherlands
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To elaborate on this a bit:

Noise is by definition a random signal, so you always have random differences between two recordings of noise with the same probability distribution. As a working hypothesis, suppose that the differences between two recordings of noise with the same probability distribution are more audible than the "average" difference between additive noise and the noise of a dithered quantizer.

You will then hear a difference in ABX tests where the same additive noise file and the same dithered and quantized file are used over and over again for all "X" trials. The same holds for ABX tests where two different additive noise files are used over and over again.

It then becomes far more difficult when an ABX test is done where each X file is generated separately. Each X file then sounds different, and you will try to categorize them as "similar to A" or "similar to B", but this categorization will depend more on the random variations between the files than on whether they have additive noise or dither and quantization noise.

This hypothesis could explain a lot:
1. Why you get significant results in the Foobar ABX tests, but not in the test with X1 to X10 files.
2. Why the results of the Foobar ABX tests were so different from what Wannamaker wrote.
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Old 1st December 2017, 07:23 AM   #79
Mooly is offline Mooly  United Kingdom
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High-order dither listening test
I believe it is often said that 'audible memory' is very unreliable and my results seem to confirm that. Although I felt there was a 'noticeable' difference, it needed an ABX test to get a statistically valid result.

Interesting
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Old 1st December 2017, 02:34 PM   #80
MarcelvdG is offline MarcelvdG  Netherlands
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That's another hypothesis that could explain the results so far. Is there any convenient way you can compare a third file against two known files without needing to rely on your auditory memory?

If we can somehow show that my hypothesis that it's all due to different realizations of the same stochastic process sounding audibly different is wrong, then we've also proven Wannamaker's claim that dithered quantization sounds exactly like noise incorrect. If not, then we are stuck with results that are open to more interpretations.

Last edited by MarcelvdG; 1st December 2017 at 02:39 PM.
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