well, let me offer this 2005 paper for consideration, then...
A small group of experts on this subject (some from this forum) is currently investigating the audibility of jitter.The idea is to develop a jitter simulation application to enable testing (listening) without a low-jitter DAC.Alternatively an ultra-low jitter DAC and ADC are available for DBT.There's no strict time schedule for the project. I'll post updates in this thread.
well, let me offer this 2005 paper for consideration, thenhttp://www.jstage.jst.go.jp/article/ast/26/1/50/_pdfAudibility threshold for timing jitter, for 'golden eared' listeners in a two-alternative forced-choice paradigm using their preferred listening environment and samples: 250 ns.
QuoteAudibility threshold for timing jitter, for 'golden eared' listeners in a two-alternative forced-choice paradigm using their preferred listening environment and samples: 250 ns.I've read this and found it largely reflects the findings of many friends. Wonder if this can be repeated exactly with a different group?
Audibility threshold for timing jitter, for 'golden eared' listeners in a two-alternative forced-choice paradigm using their preferred listening environment and samples: 250 ns.
For digital transport, jitter can be a serious killer, but it has to be pretty damn serious before it affects this layer. Basically your data lines and clock lines have to be out of sync. By a lot. If people want to simulate this, I'd recommend writing a program to either randomly delete samples or randomly rewrite a sample to the sample immediately preceding it. My guess is that this happens as often as cosmic ray memory errors.Since most applications for people with digital music is in the playback, only the DACs are relevent, and the question must be raised, "What are typical settling times for DACs?" But I think it also raises another question. Is Jitter at all relevent to people who don't know what the settling time of their DAC chip is?
The paper previously cited in this thread has actual audibility testing, and appears to set an audibility threshold of jitter of around 250ns. Papers without audibility studies set the threashold far lower. For example, Dunn's 1992 AES paper claims an audibility threshold of an astonishing 20ps at 20 KHz, based on his 1991 paper "Considerations for Interfacing Digital Audio Equipment to the Standards AES3, AES5, AES11, Proceedings of the 10th International AES Conference, 1991" (paper not yet found online). As another data point, "A Digital Discourse, Dr. Malcolm Hawksford; HiFi News & Record Review Feb,April, June, Aug, 1990" claims a peak jitter threshold of 400ps (also cited by Stereophile). I have not found the actual article yet, just citations and quotes.Is Dunn's audibility curve an analytic derivation, or an audibility study? Dunn's curve of audibility is widely quoted. Anyone have a copy of this paper? Others cited, but not yet found (I hesitate to pay the $20 AES paper fee) include "Eric Benjamin and Benjamin Gannon, "Theoretical and Audible Effects of Jitter on Digital Audio Quality", Preprint 4826 of the 105th AES Convention, San Francisco, September 1998" and "The Effects of Sampling Clock Jitter on Nyquist Sampling Analog-to-Digital Converters, and on Oversampling Delta-Sigma ADCs, 87th Convention of the Audio Engineering Society, October, 1989" (also cited by Stereophile).
Dear Jim,Thank you for the e-mail. I suppose that you read our paper titled'Detection threshold for distortions due to jitter on digitalaudio(http://www.jstage.jst.go.jp/article/ast/26/1/50/_pdf).'. Before thispaper was published in the Acoustical Science and Technology, we hadpublished another paper 'The maximum permissible size and detectionthreshold of time jitter on digital audio.' Unfortunately, it was written inJapanese.In our first experiment, which was reported in the Japanese paper, we used afixed listening condition and fixed materials. All of 14 participants wereuniversity students without any special training. The audio system that weused consisted of the following equipment.D/A converter --- SEK'D ADDA2496SpreAmp. --- Luxman C-7main Amp. --- Luxman M-7loudspeakers --- DIATONE DS-205They costed about $10,000. I don't know if they belong to high-end or not.All participants could distinguish between sounds with and without timejitter when the jitter size was 9216 ns. A few could when it was 1152 ns. Noone could when it was as small as 576 ns.There was a question, however, if the result would depend on the listeningenvironments and the skill of the listeners. That is why we carried on thesecond experiment. This second experiment is reported in the paper, the onethat you probably read.Listeners in the second experiment were all professionals, audio engineers,recording/mixing engineers, musicians, etc... Sound materials were selectedby the listeners so that each listener could use his (her) familiarmaterials. The experimenter (we) visited the listeners' studios or listeningrooms so that we could use listeners' own DAC, amplifiers, loudspeakers andheadphones. The system configurations, therefore, varied among listeners.They were mostly mid-end or above, I suppose.As you can find in the paper, some listeners could distinguish the soundswhen time jitter was 500 ns. It could not be detected, however, when thejitter was as small as 250 ns.In both experiments, there was considerable difference in listeners'performance. I don't know, however, if it was because of their audioexperience. We had expected much better performance in the second experimentbecause the listeners were professionals and they could use their favoriteenvironments and materials.Our conclusion up to now is that the normal hearing listeners' detectionthreshold for time jitter in program materials is several hundred ns.I appreciate that you are interested in our paper. Thank you for askingquestions.Best wish--ASHIHARA Kaoru
Hello Jim,Additional comments came from my co-worker, Dr. Kiryu.Prior to the second experiment, we had sent the materials with time jitterof several amounts to some of the participants. They could, therefore, trainthemselves with the materials. In fact, one listener told us that he coulddetect time jitter of several ns. However, in the experiment that was astrict double-blind test, his score was much worse as written in the paper.Recently, the materials were sent to Dr. Kiryu's friend who is anaudiophile. This man said that the sufficient training made it possible todetect time jitter of 150 ns.I want to add some more.We had considered about the maximum permissible jitter in audio packagemedia. When random time jitter does not cause any distortions larger than1/2 LSB (Least Significant Bit), it does not degrade the quality of soundsbecause the distortions in this case are smaller than the quantization noiselevel. When there is time jitter, the maximum distortion occurs where theslope of the waveform is its maximum. The size of distortion can be obtainedby multiping the slope by jitter size. Does it make sense to you? My Englishmay be awkward sometimes. Please make it up for with your imagination.Anyway, if you can find the maximum slope (inclination?) in the waveforms ofthe sound materials, you can estimate the maximum permissible jitter size.We estimated the maximum permissible jitter size by checking the maximumslope in the music waveforms in many CDs. The values varied considerablybetween 182 ps and 2567 ps. This means that in certain materials, timejitter has to be smaller than 182 ps to guarantee a 16-bit resolution.In our research, the material that was most susceptible to jitter was amusic played by a music box and it contained a lot of high-frequencycomponents. One hundred eighty-two ps correspond to the maximum permissiblejitter in a pure tone of about 13.3 kHz. If a 20 kHz pure tone has to bereproduced with a resolution of 16 bit, the maximum permissible jitter sizeis about 121 ps. By the way, I do not know any loudspeakers or headphonesthat have linearity corresponds to a 16 bit resolution. After all, I won'tbelieve someone who says that he can detect time jitter of 100 ps or less inCDs.I visited the site of Headfi.org and found your heated discussion on thistopic.Keep going!-----------------------------------------
Here's another study on the threshold of jitter:http://www.sea-acustica.es/Sevilla02/mus05001.pdf
We had considered about the maximum permissible jitter in audio packagemedia. When random time jitter does not cause any distortions larger than1/2 LSB (Least Significant Bit), it does not degrade the quality of soundsbecause the distortions in this case are smaller than the quantization noiselevel.
John, the post that you quote refers specifically to RANDOM jitter. How can this possibly produce anything remotely resembling a 3 kHz tone?
We should be able to estimate the audibility of sinusoidal jitter-induced distortion using masking theory. Has anyone published these calculations?Are there any good papers on the audibility of sinusoidal jitter?
His calculations are based upon a peak playback level of 120dB SPL and he assumes that un-masked sidebands become audible at 0 dB SPL.
See section 3.3 for an explanation, and figure 9 for a plot of "maximum inaudible jitter amplitude" vs frequency.In summary of Julian Dunn's calculations: 1us at jitter frequencies below 200 Hz should be inaudible1ns at a jitter-frequency of 600 Hz should be inaudible100 ps at a jitter-frequency of about 3 kHz should be inaudible20 ps a jitter-frequency of 20 kHz should be inaudible
A detailed paper on the derivation of theses numbers can be found here:http://www.aes.org/e-lib/browse.cfm?elib=6111
Quote from: John_Siau on 24 May, 2010, 03:48:20 PMHis calculations are based upon a peak playback level of 120dB SPL and he assumes that un-masked sidebands become audible at 0 dB SPL.Can I explain this in suitably scientific language?It's taking the Michael.QuoteSee section 3.3 for an explanation, and figure 9 for a plot of "maximum inaudible jitter amplitude" vs frequency.In summary of Julian Dunn's calculations: 1us at jitter frequencies below 200 Hz should be inaudible1ns at a jitter-frequency of 600 Hz should be inaudible100 ps at a jitter-frequency of about 3 kHz should be inaudible20 ps a jitter-frequency of 20 kHz should be inaudibleSo you need less than 20ps jitter - otherwise, when you play back 20kHz sine wave at 120dB SPL, the jitter-induced noise might have a total power equivalent to 0dB SPL.
The first fallacy here is the idea that the human threshold of hearing remains at 0 dB while a human is listening to 20 Hz at 120 dB. IOW, there is a presumption that theshold shifts never happen, even in the presence of 120 dB sounds.The second fallacy is that there would ever be a natural sound that is a 120 dB 20 Hz pure tone with all other sounds 120 dB down.The third fallacy is that there is anybody actually listens to reproduced sound in a context where the listening environment's residual noise is at 0 dB or below, other than as part of a lab esperiment.
What must be understood is that random jitter is also an extreme case that also NOT typical of real audio hardware. For this reason, the random jitter audibility test results are as unrealistic as Julian's graph.
I suspect realistic threholds for typical "real-world" jitter spectra will fall somewhere in between these extreme cases.
Both papers provide good resources for finding a more realistic answer.
We hear very little about people hearing jitter during LP playback, yet there is jitter in LP playback that is commonly less than 60 dB down.
Quote from: Arnold B. Krueger on 26 May, 2010, 11:09:26 AMWe hear very little about people hearing jitter during LP playback, yet there is jitter in LP playback that is commonly less than 60 dB down.Like, WOW, man!
I keep pointing out to people that .55555_Hz jitter isn't that bad.
BTW I found a scientific paper about this. It is called: Golden Ears and Meter Readers: The Contest for Epistemic Authority in Audiophilia
How many of the references that went into this page meet TOS 8?2?