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?

[Pio2001]

• Would such a test be useful
• Would the results of such a test be valid?
• What sort of test procedure would be best?

Yes it would be useful. Jitter is the main cause invoked in order to explain the alledged sonic difference between the digital output of a 50 € DVD player and a 10,000 € dedicated digital drive.

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.

A full scale 20 kHz sine with jitter introducing a 3.5 kHz artifact should be the most sensitive combination.

The most difficult part in this test, in my opinion, will be to get comprehensive jitter analysis from consumer CD players. Especially if jitter is signal dependant.
Jitter should also be analyzed directly at the clock output in order to account for hardware induced jitter. Some claim that heavy error correction or tracking corrections burdens the power supply, which could in turn affect the clock stability.

This post has been edited by Pio2001: Dec 27 2006, 18:39