Originally Posted by stereoeditor
Thank you or making these files available for download, Mr. Krueger. And thank you for starting each file with a 1kHz tone.
With the “No jitter” file, there are no sidebands visible, of course, and the noisefloor lies at the 16-bit level, ie, with bin values between -132 and -140dBFS. With the “Maximum” file, sidebands at 970 and 1030Hz are around 35dB below the 1kHz level, with sidebands at +/-60Hz and +/-90Hz visible at progressively lower levels. With the “Marginal, .00625” file, the primary sidebands lie around -55dB (see attached graph). With both these files, there is also a slight reduction in dynamic range evident, particularly above 10kHz, which is presumably due to the use of dither in your processing.
However, regarding using these files for listening tests to “jitter,” these spectra don’t resemble what I have found with any of the digital products I have measured over the years. I have never encountered a pair of strong sidebands at +/-30Hz.
The above analysis seems to be consistent with my own analysis of the files in question. Thanks for analyzing them and confirming my own measurements.
I have encountered jitter at 30 Hz on many occasions, and test results of that nature have been posted here by others from several sources many times.
Here's an example:
Link to this picture in context: Jitter
I have often encountered sidebands at +/-60, 120, and 180Hz, which are obviously power-supply related. (These are not necessarily due to jitter; they could also arise from insufficient power-supply rejection on the DAC chip’s voltage reference pin.) But spurious jitter tends to be much higher in frequency than 30Hz, hence much less susceptible to masking.
The above comment about masking seems to show a lack of study of the matter. The scientific literature (example Zwicker and Fastl) suggests that FM distortion is heard based on three different perceptual models depending on jitter frequency. At very low jitter frequencies, the ear simply tracks the changes. LP rotation-based jitter is usually perceived this way. Above a few Hz jitter is heard as roughness which my 30 Hz jitter samples demonstrate quite clearly. Above a few 100 Hz masking starts coming into play.
Reference Zwicker and Fastl Psychoacoustics Facts and Models (Third Edition, 2007):
Chapter 10, page 258 paragraph 10.1
(I'd reproduce the text but AVS recently totally screwed up the process of posting graphics)
As I have said in this thread several times and have demonstrated I can fabricate audio files with jitter de jour. If someone would actually give them a fair hearing, name the jitter frequency, and in due time, I'll post the files. It looks to me like I may have the sequence of levels for effective listener training and critical listening pretty close, but I have practically total control over that as well. I can also change musical selections, although the Joni Mitchell piece seems pretty diagnostic for jitter, especially near the beginning. Foobar2000 allows listening to the test tone or the music or both, by simply adjusting easy to use controls.
The primary modulation frequency of 30Hz is too high if you are trying to model the behavior of an LP player, where I have found the primary sidebands to lie at +/-8 to 12Hz, depending on the frequency of the tonearm effective mass/cartridge-suspension compliance . So I am not sure what you are trying to prove about jitter with these files. Any listening test results will not demonstrate the audibility or not of the jitter typically found in digital systems.
As I have documented, I was targeting a real world result, for which the sample provided is just one example. I suspect that 30 Hz corresponds to a common HDMI framing frequency.
It is possible that the 60 Hz results that you have obtained might be exactly what you say and are power supply related, or not. I'd probably change the power supply frequency to nail that down if that was of interest.
I am familiar with the 12 Hz jitter frequency related to tone arms as it shows up in the literature all the time. 0.555 Hz is another LP-related jitter frequency based pm 33 1/3 rpm.
Again, my major concern is not wasting my time with files that nobody listens to properly. If you want something, specify it and we can probably do something.