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High-order dither listening test
High-order dither listening test
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Old 14th November 2017, 11:52 AM   #61
udok is offline udok  Austria
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The sample with 'none' is *without* added noise. It has only quantization artefacts.

In my tests i saw, that the ratio of sampling-frequency to signal frequency is important too.

I find it very difficult to distinguish the different noise types in the sine wave example.

I did some more example with real music files.

Please listen to the files (the second one is Pavels file quantized with my version):


http://www.s1usb.com/ftp/cello1.zip


http://www.s1usb.com/ftp/drumhats1.zip

I have added different noise types and coded the file with 12 bit (13 bit for
the 11-rand noise example). The original file is included too.

Especially with the drumhats example i think i hear differences with the rectangular and the triangular noise type.
I will try the ABX test later.


One question: what program do you use for blind testing? I would like to do looping of a region.

Last edited by udok; 14th November 2017 at 12:14 PM.
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Old 14th November 2017, 12:08 PM   #62
PMA is offline PMA  Europe
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Quote:
Originally Posted by udok View Post
The sample with 'none' is *without* added noise. It has only quantization artefacts.
No dither used??
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Old 14th November 2017, 12:15 PM   #63
udok is offline udok  Austria
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yes, for the sine example above - only quantization.
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Old 14th November 2017, 05:14 PM   #64
udok is offline udok  Austria
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Added another example where each File is quantized to 13 bit:
www.s1usb.com/ftp/Bass2.zip

My listening impression is that the undithered file is the quietest.
Maybe the 13 bit quantizer is acting like a noise gate during quiet sections?

In the drumhats example the undithered file is easily recognized by the
"faint tones" in the silent section in the last quarter and the noise
in the quiet section at the beginning sounds not quite right...

The triangle sounds a bit more noisier maybe.

Last edited by udok; 14th November 2017 at 05:24 PM.
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Old 14th November 2017, 08:28 PM   #65
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by udok View Post
I looked at the spectrum too, but did not see much difference. Any
random dither seems to break the quantization tones. These tones
only occur if the sample frequency is a multiple of the signal frequency.
In normal music they should almost never appear.
Without dither, you can actually expect a line spectrum for any rational relation between signal and sample frequency. For example, 1 kHz and 44.1 kHz gives lines at multiples of 100 Hz (greatest common divisor of 1 kHz and 44.1 kHz).

1 LSB peak-to-peak uniform dither is enough to get rid of this and replace it with a white spectrum, but the level of the noise still depends on the fractional part of the signal (noise modulation). 2 LSB peak-to-peak triangular PDF dither is enough to make the power spectral density of the total error white and independent of the signal.

Stated otherwise, 2 LSB peak-to-peak triangular PDF dither is sufficient to fool a spectrum analyser, but definitely not sufficient to fool the ears of Mooly and PMA!
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Old 14th November 2017, 08:50 PM   #66
PMA is offline PMA  Europe
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Another, more realistic question (IMO playing with 4 - 8 bit resolution + dither does not make much sense).

For higher resolution, like 20 - 24 bit, would you recommend dithering for the final sound product?
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Old 14th November 2017, 08:54 PM   #67
MarcelvdG is offline MarcelvdG  Netherlands
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In my opinion, the results of this test are absolutely fascinating because they totally contradict what Wannamaker wrote in his PhD thesis (see jcx's post #5 in this thread) and in various peer-reviewed articles about the audibility of dithered quantization. I didn't expect that at all, but the test results are clear.

"For audio signal processing purposes, there seems to be little point in rendering any moments of the total error other than the first and second independent of the input. Variations in higher moments are believed to be inaudible and this has been corroborated by a large number of psycho-acoustic tests conducted by the authors and others [13, 21]."

The very first test in this thread already showed that it is not just the average and the RMS value that determine the audibility, with other words, that higher moments matter.

"When 2RPDF [ triangle PDF ] dither was employed, no instance was found in which the error was audibly distinguishable from a steady white noise entirely unrelated with the input."

The later tests show directly that this is nonsense, even with equal RMS and peak values and as similar a probability distribution as possible.

Mooly and PMA, if you are willing to listen to more noisy recordings, we could check what order of dither is required to really make dithered quantization indistinguishable from additive noise.
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Old 14th November 2017, 09:01 PM   #68
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by PMA View Post
Another, more realistic question (IMO playing with 4 - 8 bit resolution + dither does not make much sense).
I disagree; if you want to know whether higher moments are audible, this is the most sensitive test you can think of.

Quote:
Originally Posted by PMA View Post
For higher resolution, like 20 - 24 bit, would you recommend dithering for the final sound product?
Of course! In most practical cases you won't notice any difference, but when the volume is turned up so high and the music is so soft that you do hear a difference, the dithered version will always sound better.

Another question I had, and you and Mooly should know the answer to that by now: the total error with triangular dither sounds different from additive noise, as you have shown, but does it sound worse? If not, then triangular dither may still be the best compromise for audio: getting rid of the worst quantization artefacts at a limited SNR penalty.
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Old 14th November 2017, 09:01 PM   #69
PMA is offline PMA  Europe
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Marcel, you are doing a great job, but frankly, I have big troubles to listen to those noisy samples. That's why I have humbly asked you to process that almost noiseless file with added noise at 12-th bit, not the 8th or 10th.

Re "better or worse", I do not dare to answer, I was just trying to find a difference. Generally speaking, I have preferred a TPD dither to noise shaping dithers in another tests.

Last edited by PMA; 14th November 2017 at 09:04 PM.
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Old 14th November 2017, 09:53 PM   #70
MarcelvdG is offline MarcelvdG  Netherlands
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That sounds to me like you have no strong preference, not strong enough to increase the noise floor by at least another 1.25 dB for (the noise penalty when you go from second- to third-order dither).
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