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?

[John_Siau]

We had considered about the maximum permissible jitter in audio package
media. When random time jitter does not cause any distortions larger than
1/2 LSB (Least Significant Bit), it does not degrade the quality of sounds
because the distortions in this case are smaller than the quantization noise
level.

The above statement is incorrect. The quantization noise of a digital audio system does not fully mask all distortion that is at a lower level. This is a common misconception that ignores masking theory.

For example, a 3 kHz tone can be heard as much as 30 dB below the level of a white noise signal if the level of the 3 kHz tone exceeds the threshold of hearing.

Our ears are very good at detecting tones at levels that are below the level of the ambient noise.

This does not mean that the results of their paper are necessarily incorrect, it just shows that they ignored masking theory when speculating what distortion levels may be audible.

Let me say it again - just to be very clear:
1) The -96 dB FS quantization noise of a 16-bit CD system does not magically mask all distortion and music that falls below -96 dB FS.
2) 3 kHz tones can be heard in a 16-bit TPDF system down to levels as low as about -126 dB FS if system gain is turned up enough to allow the tone to be reproduced at a level that is sufficiently above the threhold of hearing.

Notes:
I intentionally selected 3 kHz - worst case (see Fletcher-Munson)