Audibility of Jitter, Proposing a series of tests Options

[cabbagerat]

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?

[punkrockdude]

What's your opinion on the difference in audible difference in my last post? What makes the behaviour? Regards.

[2Bdecided]

What's your opinion on the difference in audible difference in my last post? What makes the behaviour? Regards.

Your 05 file is a fraction of a sample earlier than your 04 file - i.e. they are not perfectly in sync. Hence they won't null out. It's somewhat difficult to correct for sub-sample delays - you'd have to add a sub-sample delay to file 05 to make it null properly. However, adding that sub-sample delay will typically change the audio a little, so it's tricky to rely on null tests in this case. It could be done, with the caveat that you'd have to ignore any differences that were due to the sub-sample delay, and hope no actual differences were hidden by this. It would be hard to convince people of the validity of a positive or negative result - especially in comparison with the convincing -100dB result you posted.

But there is some good news - the sync is good enough to run an ABX test, especially on any ABX test tool that doesn't try to implement (or lets you disable) perfect seamless switching.

Without trying an ABX test of the two files and posting your results, you have not demonstrated an audible difference. Expectation bias is too powerful a thing for anyone on this board to believe anyone who says "I hear a difference" without a passed ABX test to prove the fact.

Cheers,
David.

[Arnold B. Kruege...]

What's your opinion on the difference in audible difference in my last post? What makes the behaviour? Regards.

Your 05 file is a fraction of a sample earlier than your 04 file - i.e. they are not perfectly in sync. Hence they won't null out. It's somewhat difficult to correct for sub-sample delays - you'd have to add a sub-sample delay to file 05 to make it null properly. However, adding that sub-sample delay will typically change the audio a little, so it's tricky to rely on null tests in this case. It could be done, with the caveat that you'd have to ignore any differences that were due to the sub-sample delay, and hope no actual differences were hidden by this. It would be hard to convince people of the validity of a positive or negative result - especially in comparison with the convincing -100dB result you posted.

But there is some good news - the sync is good enough to run an ABX test, especially on any ABX test tool that doesn't try to implement (or lets you disable) perfect seamless switching.

Agreed. File synch is generally good enough if its within 1/100th of a second.

Without trying an ABX test of the two files and posting your results, you have not demonstrated an audible difference.

I don't think the OP did this consciously, but by not first doing his own test, he's effectively telling us that he doesn't have time to do things right, but figures that we have nothing better to do than to spend the necessary time doing his homework for him.

Expectation bias is too powerful a thing for anyone on this board to believe anyone who says "I hear a difference" without a passed ABX test to prove the fact.

I don't think he actually claimed an audible difference, thereby escaping the TOS 8 issue.

At any rate I fell for his ruse, tried to ABX the files and found the problem that I identified, which he now seems to want to pick a fight with me about. ;-)

He is either very ignorant or very arrogant. ;-)

I'm about ready to do the good old plonk thing. Should I spend the time to see where his IP address leads? ;-)

[2Bdecided]

At any rate I fell for his ruse, tried to ABX the files and found the problem that I identified, which he now seems to want to pick a fight with me about. ;-)

He is either very ignorant or very arrogant. ;-)

He might be confused. I couldn't follow your argument at all.

[Arnold B. Kruege...]

At any rate I fell for his ruse, tried to ABX the files and found the problem that I identified, which he now seems to want to pick a fight with me about. ;-)

He is either very ignorant or very arrogant. ;-)

He might be confused. I couldn't follow your argument at all.

Even after listening to his samples?

[2Bdecided]

At any rate I fell for his ruse, tried to ABX the files and found the problem that I identified, which he now seems to want to pick a fight with me about. ;-)

He is either very ignorant or very arrogant. ;-)

He might be confused. I couldn't follow your argument at all.

Even after listening to his samples?

Yes. They consist of a bell, then a guitar, and a bloke singing. Fine for the purposes of investigating the audibility of jitter or any other DAC error in a signal consisting of a bell, then a guitar, and a bloke singing

Of course I agree about the necessity of ABXing, and the fact it's a possible audible problem.

Cheers,
David.