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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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cabbagerat
post Dec 27 2006, 19:04
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QUOTE (Pio2001 @ Dec 27 2006, 09:39) *
The results would be valid if several conditions are fullfilled.
On top of my head I can think about
-The kind of jitter. Some kind might be audible, some kind inaudible. We must choose the kind of jitter that should cause the biggest audible effect.
-The test must be performed on a system whose jitter is small compared to the tested amount of jitter.
-The samples used must be sensitive to jitter.
All three of these are difficult problems - and would need careful test design to handle. Possibly starting with something along the lines of "is 1us of jitter audible? in test samples? in music?" and moving down to the harder problems if that test has a positive result would be a good plan. I don't know what the right solution is.

QUOTE (Gigapod @ Dec 27 2006, 09:48) *
I would dare say that none of us HA readers has the equipment to directly measure jitter with any degree of precision.
I do have access to such equipment when I am at University, and hopefully I can get another student to teach me to use it. Real measurements would be invaluable but, as Pio2001 says, if the jitter is data dependent (and it seems to be in many cases) it becomes a much harder problem.

Gigapod - you sound like you know quite a lot about jitter/phase noise - thanks for your input so far. Keep it coming smile.gif


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Gigapod
post Dec 27 2006, 19:25
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QUOTE (cabbagerat @ Dec 27 2006, 19:04) *
...
I do have access to such equipment when I am at University, and hopefully I can get another student to teach me to use it. Real measurements would be invaluable but, as Pio2001 says, if the jitter is data dependent (and it seems to be in many cases) it becomes a much harder problem.

Gigapod - you sound like you know quite a lot about jitter/phase noise - thanks for your input so far. Keep it coming smile.gif

Cabbagerat, I think it's very interesting if you can measure jitter in audio equipment in a well equipped university lab, and later determine through listening tests if it has any audible effect. I think it's always satisfying to debunk a myth with some solid experimental data, and I am highly suspicious of the whole jitter audiophile shebang.
Actually a long time ago I studied precision clocks and did some superficial documentation gathering on quartz oscillators. I think nowadays even the cheapest CD player (like the ones costing 15 euros that you can buy at the supermarket) uses a quartz clock base, because quartz is so cheap. Typically I think the jitter figures will be very low, because even with 25% jitter (highly unlikely) at 10MHz that's only 25ns, but I have no experimental data to offer to support that assertion (lack of equipment, lack of time and vague motivation).
If I may offer some guidance here, I would say, take a single piece of audio equipment (e.g. a normal CD player) to your university, find the quartz oscillator, and check the jitter at the buffered output of the quartz oscillator (not directly at the quartz leads, obviously). Of course schematics would help a lot, but if you can't find the schematics it shouldn't be too difficult to find the quartz oscillator circuitry.
BTW at 10MHz a few pF will significantly affect the waveform, so I recommend a FET active probe with 1GHz bandwidth.
If you find out the jitter is of the order of 1ns, I wouldn't bother with the listening tests... emot-science.gif

This post has been edited by Gigapod: Dec 27 2006, 23:48
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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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