In Reply to: RE: Why? posted by Thorsten on February 16, 2014 at 20:47:17:
"Jitter can be anything, from audio range pink noise (which may give a very high measured peak-peak jitter but is sonically quite harmless)"
Not a major point of disagreement here, but I would say, with apologies to Douglas Adams, that random jitter is "mostly harmless".
Jitter, of whatever form, applies modulation to the audio signal. Even if it is of the random (e.g. "pink") form this will create noise sidebands around the signal. You may not be able to see this in a single spectrum plot if the jitter spectrum is broad and the modulation index is low in that it will appear as part of the noise floor. The tip off will be that if one silences the signal the jitter noise will go away. So, for example, the presence of different levels of background noise in the presence vs. absence of a 10 kHz sine wave at high level would be a clue that these effects are taking place. Since the impact of jitter depends on the rate of change of the signal being jittered, jitter would scarcely affect a sine wave at 100 Hz of similar level. While I agree that random jitter is less harmful that signal dependent jitter, I don't agree that it is "quite harmless" unless all the modulation products are well below the system noise floor (e.g. thermal noise floor).
Jitter is just one cause of signal dependent noise, of course, and there are also issues with measurement apparatus. However, it is generally possible to "read between the lines" when looking at DAC spec sheets and review measurements to see if these effects exist. (Another big source is your bugaboo regarding sigma-delta modulators, especially the one bit variety which can not be correctly dithered so as to have noise power that is independent of signal.)
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
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Follow Ups
- Jitter: mostly harmless? - Tony Lauck 07:50:06 02/17/14 (1)
- RE: Jitter: mostly harmless? - Thorsten 10:37:38 02/17/14 (0)