Verfasst: 18.11.2011, 18:22
Hallo,
ich finde den Vorschlag toll, eine Jitter-Hörumgebung aufzubauen, um den Effekt unter kontrollierten Bedingungen erleben zu können.
Mir kam die Idee, dass vielleicht schon andere auf diese Idee gekommen sein könnten und habe im Internet danach gesucht. Dabei habe ich 2 seriös erscheinende Paper gefunden, die etwas ähnliches beschreiben. Beide Paper beschreiben Versuche, in denen Testhörer „jitterfreie“ mit „verjitterten“ Aufnahmen vergleichen, mit dem Ziel die hörbare Jitter-Grenze festzustellen. Bei beiden Papieren wird detailliert die Versuchsanordnung, das verwendete Equipment, das Programmmaterial und der Testablauf beschrieben.
Hier sind die Links auf die Paper und per cut-and-paste der jeweilige Conclusion-Abschnitt.
Kaoru Ashihara et al., “Detection threshold for distortions due to jitter on digital audio”, Acoust. Sci. & Tech. 26, 1 (2005)
http://amorgignitamorem.nl/Audio/Jitter ... 026_50.pdf
CONCLUSION
In order to determine the maximum acceptable size of
jitter on music signals, detection thresholds for artificial
random jitter were measured in a 2 alternative forced
choice procedure. Audio professionals and semi-professionals
participated in the experiments. They were allowed to
use their own listening environments and their favorite
sound materials. The results indicate that the threshold for
random jitter on program materials 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.
E. Benjamin and B. Gannon, ‘‘Theoretical and audible effects of
jitter on digital audio quality,’’ Preprint of the 105th AES
Convention, #4826 (1998).
http://www.ultrahighendforum.com/upload ... Jitter.pdf
7.0 Conclusion
The effect of clock jitter in the digital interface was studied extensively. Measurements of the jitter
spectrum of numerous digital audio sources, primarily DVD players, were conducted. A wide range of
performance was found. The jitter spectrum of a typical source can be characterized as a white noise
floor with one or many sinusoidal jitter components with a magnitude in the range of 10 ps to 10 ns
rms. The effect of jitter induced in the interface was studied and found not to be a significant factor for
short interconnection runs likely to found in a domestic environment. Several DACs and their DIRs
were measured in order to characterize the sensitivity to distortion induced by jitter. These results
were compared to each other and to results derived from simulations. Most DACs were found to be
similar to each other and to the simulation in terms of susceptibility to jitter-induced distortion. That
distortion is approximately -107+201og(F)+201og(J) dBr for sine wave signals at F kHz with J ns rms
of clock jitter.
Up-Down threshold and AB comparison listening tests were conducted to determine the threshold of
audibility for jitter-induced distortion. The threshold of audibility for pure tones was found to be about
10 ns rms at 20 kHz and higher at lower frequencies. For nearly all program material no audible
degradation was heard for any amount of jitter added below the level at which the DIR lost lock.
Certain program material was found in which an audible degradation due to jitter was heard. The
threshold of audibility for these programs was generally found to be in the range of 30 ns rms to 300 ns
rms for sinusoidal jitter. Finally, the audible degradation was found to correspond to measurable
changes in the spectrum of the program material.
The influence of jitter in causing audible distortion was found to be less than anticipated by the
authors, and less than that predicted by both the technical and consumer audio press. Jitter induced by
the digital audio interface was not found to be an audible problem for any of the program material
auditioned.
It should not be assumed that jitter-induced distortion is a non-issue. Distortion induced by jitter is a
real phenomenon and work to reduce its effects should continue. Although the threshold of audibility
was found to be relatively high in the authors' experiments, the effect of all distortions in the audio
chain is cumulative and it is reasonable to reduce them to the lowest practical levels. Manufacturers of
DACs may find the methodology for evaluating jitter susceptibility presented in this paper useful in
characterizing and presenting meaningful jitter specifications for their products.
ich finde den Vorschlag toll, eine Jitter-Hörumgebung aufzubauen, um den Effekt unter kontrollierten Bedingungen erleben zu können.
Mir kam die Idee, dass vielleicht schon andere auf diese Idee gekommen sein könnten und habe im Internet danach gesucht. Dabei habe ich 2 seriös erscheinende Paper gefunden, die etwas ähnliches beschreiben. Beide Paper beschreiben Versuche, in denen Testhörer „jitterfreie“ mit „verjitterten“ Aufnahmen vergleichen, mit dem Ziel die hörbare Jitter-Grenze festzustellen. Bei beiden Papieren wird detailliert die Versuchsanordnung, das verwendete Equipment, das Programmmaterial und der Testablauf beschrieben.
Hier sind die Links auf die Paper und per cut-and-paste der jeweilige Conclusion-Abschnitt.
Kaoru Ashihara et al., “Detection threshold for distortions due to jitter on digital audio”, Acoust. Sci. & Tech. 26, 1 (2005)
http://amorgignitamorem.nl/Audio/Jitter ... 026_50.pdf
CONCLUSION
In order to determine the maximum acceptable size of
jitter on music signals, detection thresholds for artificial
random jitter were measured in a 2 alternative forced
choice procedure. Audio professionals and semi-professionals
participated in the experiments. They were allowed to
use their own listening environments and their favorite
sound materials. The results indicate that the threshold for
random jitter on program materials 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.
E. Benjamin and B. Gannon, ‘‘Theoretical and audible effects of
jitter on digital audio quality,’’ Preprint of the 105th AES
Convention, #4826 (1998).
http://www.ultrahighendforum.com/upload ... Jitter.pdf
7.0 Conclusion
The effect of clock jitter in the digital interface was studied extensively. Measurements of the jitter
spectrum of numerous digital audio sources, primarily DVD players, were conducted. A wide range of
performance was found. The jitter spectrum of a typical source can be characterized as a white noise
floor with one or many sinusoidal jitter components with a magnitude in the range of 10 ps to 10 ns
rms. The effect of jitter induced in the interface was studied and found not to be a significant factor for
short interconnection runs likely to found in a domestic environment. Several DACs and their DIRs
were measured in order to characterize the sensitivity to distortion induced by jitter. These results
were compared to each other and to results derived from simulations. Most DACs were found to be
similar to each other and to the simulation in terms of susceptibility to jitter-induced distortion. That
distortion is approximately -107+201og(F)+201og(J) dBr for sine wave signals at F kHz with J ns rms
of clock jitter.
Up-Down threshold and AB comparison listening tests were conducted to determine the threshold of
audibility for jitter-induced distortion. The threshold of audibility for pure tones was found to be about
10 ns rms at 20 kHz and higher at lower frequencies. For nearly all program material no audible
degradation was heard for any amount of jitter added below the level at which the DIR lost lock.
Certain program material was found in which an audible degradation due to jitter was heard. The
threshold of audibility for these programs was generally found to be in the range of 30 ns rms to 300 ns
rms for sinusoidal jitter. Finally, the audible degradation was found to correspond to measurable
changes in the spectrum of the program material.
The influence of jitter in causing audible distortion was found to be less than anticipated by the
authors, and less than that predicted by both the technical and consumer audio press. Jitter induced by
the digital audio interface was not found to be an audible problem for any of the program material
auditioned.
It should not be assumed that jitter-induced distortion is a non-issue. Distortion induced by jitter is a
real phenomenon and work to reduce its effects should continue. Although the threshold of audibility
was found to be relatively high in the authors' experiments, the effect of all distortions in the audio
chain is cumulative and it is reasonable to reduce them to the lowest practical levels. Manufacturers of
DACs may find the methodology for evaluating jitter susceptibility presented in this paper useful in
characterizing and presenting meaningful jitter specifications for their products.