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Audibility of Jitter, Proposing a series of tests
cabbagerat
post Dec 27 2006, 14:33
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The threshold of audibility of phase noise in ADC and DAC clocks is a fairly contentious issue in the HiFi and audiophile world. Some sources claim that jitter is clearly audible at low levels, and some claim that high levels of jitter are inaudible. The literature describes several tests, many with conflicting results.

One of the chief difficulties in testing the audibility of jitter is that it requires a complex hardware setup, which means that many listeners would be required to be present for an time consuming (and expensive) on site test. Over the last couple of months I have been thinking about organising a distributed listening test to look at the audibility of jitter in audio applications, based on algorithms for simulating the effects of jitter on signals. These algorithms are fairly well described in RF and telecomms engineering literature, and would be interesting for comparison purposes.

The kind of thing I have in mind is this:
Use samples which are accepted to sound good -> simulate jitter -> perform listening tests -> perform more tests at different levels of jitter depending on results

The purpose of this thread is to get ideas of the Hydrogenaudio community about performing these tests. Some of the things I would appreciate input on are:
  • Would such a test be useful
  • Would the results of such a test be valid?
  • What sort of test procedure would be best?


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pdq
post May 24 2010, 16:57
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John, the post that you quote refers specifically to RANDOM jitter. How can this possibly produce anything remotely resembling a 3 kHz tone?
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John_Siau
post May 24 2010, 18:15
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QUOTE (pdq @ May 24 2010, 11:57) *
John, the post that you quote refers specifically to RANDOM jitter. How can this possibly produce anything remotely resembling a 3 kHz tone?

Thanks for the correction - I failed to note that their paper was confined to random jitter. The distortion caused by this random jitter should be much less audible than the distortion caused by siusoidal jitter.

To reach audibility, the distortion caused by random jitter may need to be 20 to 30 dB higher than the distortion caused by sinusoidal jitter.

The "random jitter" used in this experiment is frequency limited by the Nyquist theorem. Consequently, the jitter-induced distortion will have nearly the same spectral shape as the jitter. If the spectrum of the band-limited random jitter is white, we should expect the spectrum of the jitter-induced distortion to be nearly white. TPDF dither noise will be very effective at masking this spectrally-white jitter-induced distortion. If the jitter-induced distortion is the same amplitude as 16-bit TPDF dither noise, the system noise level will increase by 3 dB. If the jitter-induced distortion is 6 dB lower than the 16-bit TPDF noise, system noise will increase by 1 dB. In this experiment, the jitter-induced distortion is simply a white noise signal that gets added to the system noise.

Note: Use RMS noise summing equations to calculate resulting noise.

Digital audio transmission systems tend to generate jitter at very specific frequencies. The spectrum of the code-induced jitter at the end of a S/PIF cable is much closer to sinusoidal than random. Spectrally white random jitter is not likely to occur in the real world. Jitter composed one or two dominant sinusoidal frequencies is much more common. In my opinion it is more important to investigate the audibility thresholds for sinusoidal jitter.

Obviously the investigation of random jitter is a good first step as it requires far fewer tests than an investigation of random jitter. With random jitter we have one variable - amplitude. An investigation of sinusoidal jitter would require two variables - amplitude and frequency. Many tests would be required to plot the audibility curves.

We should be able to estimate the audibility of sinusoidal jitter-induced distortion using masking theory. Has anyone published these calculations?

Are there any good papers on the audibility of sinsoidal jitter?

This post has been edited by John_Siau: May 24 2010, 18:19


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John_Siau
post May 24 2010, 20:48
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QUOTE (John_Siau @ May 24 2010, 13:15) *
We should be able to estimate the audibility of sinusoidal jitter-induced distortion using masking theory. Has anyone published these calculations?

Are there any good papers on the audibility of sinusoidal jitter?



Julian Dunn calculated the audibility threshold of jitter-induced sidebands produced by sinusoidal jitter. He took making effects into account when calculating audibility. His calculations are based upon a peak playback level of 120dB SPL and he assumes that un-masked sidebands become audible at 0 dB SPL.

Peak playback levels are usually lower than 120 dB SPL, and audibility thresholds will usually be slightly higher than 0 dB SPL (due to ambient noise), so his jitter-audibility plot is a worst-case audibility plot. These results could be scaled for other playback levels and ambient noise levels.

http://citeseerx.ist.psu.edu/viewdoc/downl...p1&type=pdf

See section 3.3 for an explanation, and figure 9 for a plot of "maximum inaudible jitter amplitude" vs frequency.

In summary of Julian Dunn's calculations:
1us at jitter frequencies below 200 Hz should be inaudible
1ns at a jitter-frequency of 600 Hz should be inaudible
100 ps at a jitter-frequency of about 3 kHz should be inaudible
20 ps a jitter-frequency of 20 kHz should be inaudible


A detailed paper on the derivation of theses numbers can be found here:

http://www.aes.org/e-lib/browse.cfm?elib=6111



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2Bdecided
post May 25 2010, 09:12
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QUOTE (John_Siau @ May 24 2010, 20:48) *
His calculations are based upon a peak playback level of 120dB SPL and he assumes that un-masked sidebands become audible at 0 dB SPL.
Can I explain this in suitably scientific language?

It's taking the Michael.


QUOTE
See section 3.3 for an explanation, and figure 9 for a plot of "maximum inaudible jitter amplitude" vs frequency.

In summary of Julian Dunn's calculations:
1us at jitter frequencies below 200 Hz should be inaudible
1ns at a jitter-frequency of 600 Hz should be inaudible
100 ps at a jitter-frequency of about 3 kHz should be inaudible
20 ps a jitter-frequency of 20 kHz should be inaudible
So you need less than 20ps jitter - otherwise, when you play back 20kHz sine wave at 120dB SPL, the jitter-induced noise might have a total power equivalent to 0dB SPL.


QUOTE
A detailed paper on the derivation of theses numbers can be found here:

http://www.aes.org/e-lib/browse.cfm?elib=6111
I didn't even need to look - the derivation is obvious - it's the starting point that's silly. (IMO - YMMV!)

Cheers,
David.

This post has been edited by 2Bdecided: May 25 2010, 09:12
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Arnold B. Kruege...
post May 25 2010, 14:04
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QUOTE (2Bdecided @ May 25 2010, 04:12) *
QUOTE (John_Siau @ May 24 2010, 20:48) *
His calculations are based upon a peak playback level of 120dB SPL and he assumes that un-masked sidebands become audible at 0 dB SPL.
Can I explain this in suitably scientific language?

It's taking the Michael.


QUOTE
See section 3.3 for an explanation, and figure 9 for a plot of "maximum inaudible jitter amplitude" vs frequency.

In summary of Julian Dunn's calculations:
1us at jitter frequencies below 200 Hz should be inaudible
1ns at a jitter-frequency of 600 Hz should be inaudible
100 ps at a jitter-frequency of about 3 kHz should be inaudible
20 ps a jitter-frequency of 20 kHz should be inaudible
So you need less than 20ps jitter - otherwise, when you play back 20kHz sine wave at 120dB SPL, the jitter-induced noise might have a total power equivalent to 0dB SPL.


The first fallacy here is the idea that the human threshold of hearing remains at 0 dB while a human is listening to 20 Hz at 120 dB. IOW, there is a presumption that theshold shifts never happen, even in the presence of 120 dB sounds.

The second fallacy is that there would ever be a natural sound that is a 120 dB 20 Hz pure tone with all other sounds 120 dB down.

The third fallacy is that there is anybody actually listens to reproduced sound in a context where the listening environment's residual noise is at 0 dB or below, other than as part of a lab esperiment.

I think I'll stop now! ;-)
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John_Siau
post May 25 2010, 18:09
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QUOTE (Arnold B. Krueger @ May 25 2010, 09:04) *
The first fallacy here is the idea that the human threshold of hearing remains at 0 dB while a human is listening to 20 Hz at 120 dB. IOW, there is a presumption that theshold shifts never happen, even in the presence of 120 dB sounds.

The second fallacy is that there would ever be a natural sound that is a 120 dB 20 Hz pure tone with all other sounds 120 dB down.

The third fallacy is that there is anybody actually listens to reproduced sound in a context where the listening environment's residual noise is at 0 dB or below, other than as part of a lab esperiment.


I don't disagree with any of these comments. Julian Dunn never claimed that jitter becomes audible at these levels, just that we could guarantee that it would be inaudible if held below these levels.

In my post, I suggested that we could scale Julian Dunn's calculations to reasonable listening situations. I was not implying that these levels were typical, or that full-scale 20 kHz tones are found in any music recordings.

With a little more work, we could also adjust Julian's calculations for an audio input spectrum that is more typical of music.

What must be understood is that random jitter is also an extrreme case that also NOT typical of real audio hardware. For this reason, the random jitter audibility test results are as unrealistic as Julian's graph. I suspect realistic threholds for typical "real-world" jitter spectra will fall somewhere in between these extreeme cases.

Both papers provide good resources for finding a more realistic answer.

This post has been edited by John_Siau: May 25 2010, 18:15


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Arnold B. Kruege...
post May 26 2010, 16:09
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QUOTE (John_Siau @ May 25 2010, 13:09) *
What must be understood is that random jitter is also an extreme case that also NOT typical of real audio hardware. For this reason, the random jitter audibility test results are as unrealistic as Julian's graph.


I agree that random jitter is one of the extreme cases. It should in general be the hardest to hear because it lacks tonality. Its cause is likely to be irreducable thermal noise.

IME most jitter traces back to the environment or the process. Power supply frequencies are common. Jitter at the same rate as data blocks is not uncommon. Then there are the cases where the signal jitters itself.

QUOTE
I suspect realistic threholds for typical "real-world" jitter spectra will fall somewhere in between these extreme cases.


So far I see none of the cases where jitter is really hard to discern, just different cases that are extremely small.

When all possible forms of masking are consdered, the amount of jitter that can be masked can be huge. I'm not sure that I can support those cases being used to calculate an average of extreme cases.

We hear very little about people hearing jitter during LP playback, yet there is jitter in LP playback that is commonly less than 60 dB down.

QUOTE
Both papers provide good resources for finding a more realistic answer.


They may be a starting point.
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Woodinville
post May 26 2010, 18:36
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QUOTE (Arnold B. Krueger @ May 26 2010, 08:09) *
We hear very little about people hearing jitter during LP playback, yet there is jitter in LP playback that is commonly less than 60 dB down.


Like, WOW, man! smile.gif

I keep pointing out to people that .55555_Hz jitter isn't that bad.


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Posts in this topic
- cabbagerat   Audibility of Jitter   Dec 27 2006, 14:33
- - Gigapod   QUOTE (cabbagerat @ Dec 27 2006, 14:33) T...   Dec 27 2006, 16:27
|- - Arnold B. Krueger   QUOTE (Gigapod @ Dec 27 2006, 11:27) QUOT...   Sep 26 2013, 03:48
|- - stv014   Not sure if this is relevant here, but there is cu...   Sep 26 2013, 10:56
|- - Arnold B. Krueger   QUOTE (stv014 @ Sep 26 2013, 05:56) Not s...   Sep 26 2013, 12:35
|- - stv014   QUOTE (Arnold B. Krueger @ Sep 26 2013, 13...   Sep 27 2013, 10:53
- - dariju   There is a good article about jitter @ Digital Dom...   Dec 27 2006, 17:07
|- - Gigapod   QUOTE (dariju @ Dec 27 2006, 17:07) There...   Dec 27 2006, 17:35
|- - Zster   QUOTE (Gigapod @ Dec 27 2006, 18:35) QUOT...   Dec 28 2006, 11:31
|- - Gigapod   QUOTE (Zster @ Dec 28 2006, 11:31) ... He...   Dec 28 2006, 12:30
- - cabbagerat   QUOTE (Gigapod @ Dec 27 2006, 07:27) I wo...   Dec 27 2006, 17:28
|- - Gigapod   QUOTE (cabbagerat @ Dec 27 2006, 17:28) ....   Dec 27 2006, 18:03
- - Pio2001   QUOTE (cabbagerat @ Dec 27 2006, 14:33) W...   Dec 27 2006, 18:39
|- - Gigapod   QUOTE (Pio2001 @ Dec 27 2006, 18:39) ... ...   Dec 27 2006, 18:48
- - cabbagerat   QUOTE (Pio2001 @ Dec 27 2006, 09:39) The ...   Dec 27 2006, 19:04
|- - Gigapod   QUOTE (cabbagerat @ Dec 27 2006, 19:04) ....   Dec 27 2006, 19:25
- - cabbagerat   QUOTE (Gigapod @ Dec 28 2006, 03:30) Cabb...   Dec 28 2006, 20:56
|- - Gigapod   QUOTE (cabbagerat @ Dec 28 2006, 20:56) ....   Dec 29 2006, 04:37
- - wimms   Jitter matters only during slope of the signal. In...   Dec 29 2006, 16:00
|- - Gigapod   QUOTE (wimms @ Dec 29 2006, 16:00) ... C1...   Dec 29 2006, 16:34
- - cabbagerat   The second one of those paper is fascinating. It...   Dec 29 2006, 18:25
|- - krabapple   QUOTE (cabbagerat @ Dec 29 2006, 12:25) T...   Jan 13 2007, 00:11
|- - Gigapod   QUOTE (krabapple @ Jan 13 2007, 00:11) .....   Jan 13 2007, 00:30
- - krabapple   well, let me offer this 2005 paper for considerati...   Jan 13 2007, 04:32
|- - Woodinville   QUOTE (krabapple @ Jan 12 2007, 19:32) we...   Jan 13 2007, 08:30
||- - Kees de Visser   For the Dutch speaking and jitter interested reade...   Jan 13 2007, 18:36
|- - Eric Carroll   QUOTE (krabapple @ Jan 12 2007, 22:32) we...   Mar 3 2007, 07:07
||- - Kees de Visser   A small group of experts on this subject (some fro...   Mar 3 2007, 12:34
|||- - jlohl   QUOTE (Kees de Visser @ Mar 3 2007, 12:34...   Mar 4 2007, 10:14
||- - 2Bdecided   QUOTE (Eric Carroll @ Mar 3 2007, 06:07) ...   Mar 21 2007, 12:31
||- - udauda   Here's another study on the threshold of jitte...   Aug 14 2009, 22:12
||- - udauda   http://www.jstage.jst.go.jp/article/ast/26/1/50/_p...   Aug 14 2009, 22:45
||- - Arnold B. Krueger   QUOTE (udauda @ Aug 14 2009, 17:12) Here...   Aug 16 2009, 11:50
|- - DonnieW   QUOTE (krabapple @ Jan 12 2007, 22:32) we...   Mar 5 2007, 00:52
|- - Kees de Visser   QUOTE (DonnieW @ Mar 5 2007, 00:52) QUOTE...   Mar 5 2007, 07:00
- - DualIP   For tests, why not generate a simple program that ...   Jan 14 2007, 09:14
- - knutinh   Correlated jitter is probably worse than random ji...   Jan 14 2007, 17:59
- - cabbagerat   QUOTE (DualIP @ Jan 14 2007, 00:14) For t...   Jan 16 2007, 09:18
- - sthayashi   Is this the wrong place to ask "What IS Jitte...   Mar 4 2007, 11:32
|- - mcbear   QUOTE (sthayashi @ Mar 4 2007, 11:32) For...   Mar 21 2007, 11:05
- - hlloyge   Well, bumping the old thread - has the test been c...   Feb 9 2010, 19:21
- - John_Siau   QUOTE (udauda @ Aug 14 2009, 17:45) We ha...   May 24 2010, 16:25
- - pdq   John, the post that you quote refers specifically ...   May 24 2010, 16:57
|- - John_Siau   QUOTE (pdq @ May 24 2010, 11:57) John, th...   May 24 2010, 18:15
|- - John_Siau   QUOTE (John_Siau @ May 24 2010, 13:15) We...   May 24 2010, 20:48
|- - 2Bdecided   QUOTE (John_Siau @ May 24 2010, 20:48) Hi...   May 25 2010, 09:12
|- - Arnold B. Krueger   QUOTE (2Bdecided @ May 25 2010, 04:12) QU...   May 25 2010, 14:04
|- - John_Siau   QUOTE (Arnold B. Krueger @ May 25 2010, 09...   May 25 2010, 18:09
|- - Arnold B. Krueger   QUOTE (John_Siau @ May 25 2010, 13:09) Wh...   May 26 2010, 16:09
|- - Woodinville   QUOTE (Arnold B. Krueger @ May 26 2010, 08...   May 26 2010, 18:36
|- - Arnold B. Krueger   QUOTE (Woodinville @ May 26 2010, 13:36) ...   May 26 2010, 20:06
- - punkrockdude   I have not read everything but here is a test I di...   Oct 11 2012, 21:01
- - punkrockdude   What's your opinion on the difference in audib...   Oct 14 2012, 13:38
|- - Arnold B. Krueger   QUOTE (punkrockdude @ Oct 14 2012, 08:38)...   Oct 15 2012, 14:48
||- - punkrockdude   QUOTE (Arnold B. Krueger @ Oct 15 2012, 15...   Oct 22 2012, 19:49
||- - Arnold B. Krueger   QUOTE (punkrockdude @ Oct 22 2012, 14:49)...   Oct 22 2012, 20:34
||- - punkrockdude   QUOTE (Arnold B. Krueger @ Oct 22 2012, 21...   Oct 22 2012, 21:40
|- - 2Bdecided   QUOTE (punkrockdude @ Oct 14 2012, 13:38)...   Oct 23 2012, 11:14
|- - Arnold B. Krueger   QUOTE (2Bdecided @ Oct 23 2012, 06:14) QU...   Oct 23 2012, 13:41
|- - 2Bdecided   QUOTE (Arnold B. Krueger @ Oct 23 2012, 13...   Oct 23 2012, 17:22
|- - Arnold B. Krueger   QUOTE (2Bdecided @ Oct 23 2012, 12:22) QU...   Oct 23 2012, 20:12
|- - 2Bdecided   QUOTE (Arnold B. Krueger @ Oct 23 2012, 20...   Oct 24 2012, 10:02
- - punkrockdude   2Bdecided: Interesting about subsamples. So there ...   Oct 23 2012, 12:26
|- - Arnold B. Krueger   QUOTE (punkrockdude @ Oct 23 2012, 07:26)...   Oct 23 2012, 13:32
|- - 2Bdecided   QUOTE (punkrockdude @ Oct 23 2012, 12:26)...   Oct 23 2012, 17:21
|- - Kees de Visser   To illustrate the importance of sub-sample accurac...   Oct 23 2012, 18:21
- - dhromed   File 2 and 3 null out almost perfectly. Amplificat...   Oct 23 2012, 13:25
|- - pdq   QUOTE (dhromed @ Oct 23 2012, 08:25) 4 an...   Oct 23 2012, 16:16
|- - 2Bdecided   QUOTE (pdq @ Oct 23 2012, 16:16) QUOTE (d...   Oct 23 2012, 17:30
|- - pdq   QUOTE (2Bdecided @ Oct 23 2012, 12:30) QU...   Oct 23 2012, 18:53
- - krabapple   FWIW, here's a good faith attempt to supply ex...   Sep 24 2013, 17:52
|- - Arnold B. Krueger   QUOTE (krabapple @ Sep 24 2013, 12:52) FW...   Sep 26 2013, 03:31
|- - krabapple   QUOTE (Arnold B. Krueger @ Sep 25 2013, 22...   Sep 27 2013, 02:59
|- - Arnold B. Krueger   QUOTE (krabapple @ Sep 26 2013, 21:59) QU...   Sep 28 2013, 14:32
- - 2Bdecided   I think UltimateMusicSnob is becoming the new Guru...   Sep 27 2013, 13:04
- - Wombat   QUOTE (2Bdecided @ Sep 27 2013, 14:04) I ...   Sep 27 2013, 14:38
- - 2Bdecided   Don't joke, a similar thought had crossed my m...   Sep 27 2013, 17:35
- - Wombat   i already made up my mind when he described things...   Sep 27 2013, 19:46
- - greynol   It's difficult to describe the tonality of noi...   Sep 27 2013, 19:56


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