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"Detection threshold for distortions due to jitter in digital audio"
Ashihara et al.,. Acoustical Science and Technology 26, 1 (2005)
"Benjamin and Gannon (AES preprint 4826, 1998) made an attempt to measure thresholds of audibility for sinusoidal jitter on program material. Their study seems to have a few problems, however. In their study, a special arrangement was made to the reproduction system in order to add jitter at the digital interface. It is not known if such an arrangement might change sound quality and affect the results. Secondly, they employed a self-administered threshold evaluation in which the listeners determined their thresholds at their discretion. Their results might contain errors due to the cognitive factor.""As Benjamin and Gannon reported, detection thresholds for jitter may depend on how well the listeners are trained."
"Listeners in the present study were audio professionals or semi-professionals who were supposed to be well-trained listeners. They were audio critics, sound engineers and musicians."
"Experiments were carried out in the listening booth or studio that each listener had offered. The examiner only brought there a personal computer with digital audio interface and a mouse and each listener provided his or her favorite DAC, amplifiers and loudspeakers."
"A software simulator of jitter was used. The distorted versions [of the raw PCM data] were prepared by adding artificial random jitter of various amounts ("Simulation of sound degradation due to time jitter on digital audio", Ashihara et al., J. of the Acoustical Society of Japan, 58, 232-238 (2002)). Although most of these materials were music sound recorded on commercial package media, there were also recordings from radio dramas."
"Discrimination tests were performed in a 2 alternative forced choice paradigm. Each run consisted of a full reproduction of a material. The duration of sound materials ranged from about 2min. to 4min. During a run, two versions of the same material were simultaneously reproduced. They were a reference version without jitter and an artificially jittered version. Only one of them could be presented acoustically in the foreground while the other was reproduced in the background (muted). the foreground and the background could be switched by a listener at any moment in the run."
"A PC monitor was placed in front of a listener. On its screen, three buttons were displayed. Each button was labeled either A, B, or X, respectively.""It can be concluded that detection threshold for random jitter added to program materials is several hundreds ns even for well-trained listeners under their preferable listening conditions. In some contents of conventional CDs, it had been observed that jitter had to be as small as several hundreds ps to preserve the resolution of 16 bits ("The maximum permissible size and detection threshold of time jitter on digital audio", Ashihara et al., J of the Acoustical Society of Japan, 59, 241-249 (2003)). This is way below the detection threshold values. Nishimura et al. made attempts to measure actual jitter of various DA systems during reproduction of music signals. They could not detect any jitter larger than 3 ns in their measurements (“Measurement of sampling jitter using a musical signal”, Nishimura et al., AES paper 5797)
"So far, actual jitter in consumer products seems to be too small to be detected at least for reproduction of music signals."
“The results indicate that the threshold for random jitter on program material is several hundreds ns for well-trained listeners under their preferable listening conditions. The threshold values seem to be sufficiently larger than the jitter actually observed in various consumer products.”
Follow Ups:
This covers random jitter. What about signal correlated jitter?
As it is described in"A jitter simulator on digital data"
Kiryu et al, AES convention preprint no, 5390, 2001
Even so, if jitter isn't random the spectrum of the jitter apparently plays a role in audibility.
Good question!Do you think "random jitter" might have an affect something like dithering?
It's been known for a while that random jitter is not as audible as certain types of correlated jitter. Some jitter reducing products actually claim to work by converting correlated jitter to random jitter.
"Do you think 'random jitter' might have an affect something like dithering?"The two elements are totally unrelated....
Dither is a process where noise is applied prior to A/D conversion and/or wordlength reduction to mitigate losses in resolution. Jitter is variation of sample timing during playback.
Since the words themselves "sound" similar, I've encountered comments where one term was used but the other was meant. I wouldn't be surprised if I did this personally.
I have been known to dither and get the jitters from time-to-time myself!
Hi there> "Do you think 'random jitter' might have an affect something like
> dithering?"
>
> The two elements are totally unrelated....I used the wrong word.
Instead of "affect", I should have used "effect".
"Do you think 'random jitter' might have an (audible) effect something like dithering?"Regards
"Do you think 'random jitter' might have an (audible) effect something like dithering?"Unlikely. Dither done well is almost inaudible, aside from the low-level information in the signal being easier to discern. But jitter shouldn't have an effect on this.
Advertising audio products is about on the same level as advertizing wrinkle cream and vaginal odor products.
I too thought jitter correction was snakeoil until I actually placed a digital signal conditioner into my system.I have said it before, I was completely floored at the difference that just a better clocked signal can make. I am using a NON-OS DAC and it may be more sensitive to jitter, but the difference was quite striking.
Most of you would not think twice when someone says they can hear an improvement moving to one transport to another... well what do you think is basically the only differences in *transports*? Digital signal quality.
So I don't know why people couldn't imagine reclocking the signal of a low end CDP would not make a difference.
I think that some of the marketing of these products might be BS just like alot of pseudo-scientific marketroid speak (that is my 10%)... but when you understand what a DIP does you can understand the kind of improvement that it can make to a lower end transport and appreciate that improvement for what it is.
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