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High-order dither listening test
High-order dither listening test
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Old 11th November 2017, 06:40 PM   #21
PMA is offline PMA  Europe
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Quote:
Originally Posted by MarcelvdG View Post

I think this shows that the subjective noise level depends on the probability distribution as well as on the RMS value. That's actually why the ITU-R 468 standard prescribes a quasi-peak detector rather than an RMS detector. It also means that we're not going to find out anything about the audibility of the higher-order moments this way, because I don't know how to subjectively level match the noise.

In any case, you didn't complain about distortion, so apparently the dithered quantization error sounded like noise to you for both cases.

Thanks for participating!
- I agree with your comments re subjective noise level dependence on probability distribution

- I did no complain about distortion specifically but I did complain about overall file sound qualities (defined it as "defective" and asked you if you checked sound quality of the samples), so it depends if distortion is meant as non-linear distortion only or the meaning of the term distortion is more complex. If the later is considered, then I definitely complained.

- Thanks for the test!
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Old 11th November 2017, 07:25 PM   #22
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by Mooly View Post
I didn't so much notice a difference in noise level, more a difference in the makeup of the noise. Silvery7 seems more 'granular', not as smooth for want of a better word.
That gives me an idea for a new test: triangular PDF and quantization versus pure additive noise made of the sum of three uniformly distributed noise signals. To be continued!
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Old 11th November 2017, 09:20 PM   #23
MarcelvdG is offline MarcelvdG  Netherlands
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I put two new files on WeTransfer, with the same music fragment, but now with 6.02 dB less noise:

WeTransfer

One file is rounded to 8 bits with triangular dither, the other is a floating point file with additive noise. The RMS levels of the quantization+dither noise and the additive noise match within 0.01 dB, the peak levels within 0.09 dB.

Again, please do an ABX test if you think you hear or might hear a difference and report the results of all such trials.
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Old 11th November 2017, 09:33 PM   #24
PMA is offline PMA  Europe
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What is the goal of these tests with super noisy and highly distorted files? (the "holiday" word, just to pick up one example, is unlistenable). Are you working on some new compression algorithm as a professional? Shall we expect 8-bit or 4-bit music in future? The current practices in consumer music mastering tend to admit that.
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Old 11th November 2017, 10:12 PM   #25
MarcelvdG is offline MarcelvdG  Netherlands
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I am a professional electronics engineer, but my work generally has little to do with audio and besides, at work I'm not allowed anywhere near anything digital. I certainly don't work on audio compression algorithms.

In fact I'm just curious to know whether the assumption that the total error of a dithered quantizer is indistinguishable from additive noise is correct. I could make the dither+quantization noise much weaker for the test, but that doesn't seem to make sense as it is the noise that interests me.

By the way, I used a fragment from an unprocessed live recording from an amateur chorus. I don't think the recording is distorted, sometimes some of them just sing off key.
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Old 11th November 2017, 10:57 PM   #26
udok is offline udok  Austria
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The quanization error is white noise, if the audio signal is clearly above the noise level.

You can test this simply by doing a FFT plot. White noise is independent of frequency.

Up to now i have assumed that additive dithering noise should be equally distributed
in the interval [-LSB, +LSB] (or maybe somewhat less, but a range of 1 LSB is not enough).

Why do you use a triangular distribution?

Do you have a script doing the 11'th order dithering to play with?
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Old 12th November 2017, 07:20 AM   #27
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by udok View Post
The quanization error is white noise, if the audio signal is clearly above the noise level.
This is the old theory of Bennett, that only holds when there is no rational relation between signal frequencies and sample rate.

Quote:
Originally Posted by udok View Post
You can test this simply by doing a FFT plot. White noise is independent of frequency.
Try it with a soft digitally generated sine wave of which the frequency has a simple rational relation to the sample rate and you will see completely messed up spectra. For example, a 1 kHz sine wave of a few LSB peak-peak at 44.1 kHz sample rate will give you distortion products at all multiples of 100 Hz, 100 Hz being the greatest common divisor of 1 kHz and 44.1 kHz.

Quote:
Originally Posted by udok View Post
Up to now i have assumed that additive dithering noise should be equally distributed in the interval [-LSB, +LSB] (or maybe somewhat less, but a range of 1 LSB is not enough).

Why do you use a triangular distribution?

Do you have a script doing the 11'th order dithering to play with?
Uniformly distributed dither from -0.5 LSB to +0.5 LSB makes the mathematical expectation (ensemble average) of the error independent from the signal, which eliminates the distortion peaks in the spectrum, but you still have modulation of the RMS level of the noise by the signal. With triangular noise from -1 LSB to +1 LSB, you also get rid of that.

I use a simple expression in GoldWave for the dither:
Triangular:
wave(n)+rnd(1/y)+rnd(1/y)-1/y with y = 128 for 8 bits, 32768 for 16 bits

11th order:
wave(n)+rnd(1/y)+rnd(1/y)+rnd(1/y)+rnd(1/y)+rnd(1/y)+rnd(1/y)+rnd(1/y)+rnd(1/y)+rnd(1/y)+rnd(1/y)+rnd(1/y)-5.5/y

To get a signal rounded to 7 bits, I half it, apply 8-bits dither, save it as an 8-bits file, close it, open it again, multiply everything by two and save it again.
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Old 12th November 2017, 08:00 AM   #28
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I am familiar with TPD dither and various noise shaping dithers, but did not know the 11th order dither.

BTW, I am sure that you know that your 8bit sample from your latest noise added test has seemingly 50% DC offset, at 128th amplitude level, half of the 8bit scale. Is it OK? Probably yes, just only sample value convention for 8bits?

Last edited by PMA; 12th November 2017 at 08:29 AM.
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Old 12th November 2017, 08:27 AM   #29
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Marcel, BTW, I have played a bit with your 8bit file, would you mind to listen to the result?

http://pmacura.cz/silverysea8bitnr.zip

The original recording might have been quite nice.

Edit: attached is the removed noise spectrum
Attached Images
File Type: png silvery8removed.PNG (103.5 KB, 63 views)

Last edited by PMA; 12th November 2017 at 08:56 AM.
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Old 12th November 2017, 09:43 AM   #30
MarcelvdG is offline MarcelvdG  Netherlands
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It sounds OK until the women start singing, then you hear all the artefacts of the noise removing algorithm.

To satisfy your curiosity, I've put the recording without extra noise or requantization here:

WeTransfer
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