K
knutinh
Gjest
Merk at dette er "random jitter". Båndbredde oppgis såvidt jeg ser ikke. Korrelert jitter antas å være mer hørbart, men er kanskje mest aktuel for spdif?
http://www.jstage.jst.go.jp/article/ast/26/1/50/_pdf
"
Abstract:
Detection threshold for distortions due to time jitter was measured in a 2 alternative
forced choice paradigm with switching sounds. Music signals with random jitter were simulated
digital domain. The size of jitter was arbitrary controlled so that the detection threshold could
estimated. Professional audio engineers, sound engineers, audio critics and semi-professional
musicians participated as listeners. The listeners were allowed to use their own listening environments
and their favorite sound materials. It was shown that the detection threshold for random jitter
several hundreds ns for well-trained listeners under their preferable listening conditions.
...
When the jitter size was 2 ms (r.m.s.), all listeners
scored more than 75% correct. About 25% of the listeners
detected jitter when its size was 500 ns. When it was
250 ns, however, no listener could discriminate the sounds.
The thresholds for random jitter added to program
materials seem to be several hundreds ns. Ashihara and
Kiryu [3] measured detection thresholds for random jitter
in a fixed listening condition. 14 listeners without special
training participated. Some listeners could detect jitter of
1,152 ns but no one detected jitter of 576 ns in their study.
Even though they used a fixed condition and nonprofessional
listeners, their result is comparable to the
present result. Tomizawa et al. [5] measured detection
threshold for artificial jitter under the headphone listening
condition. In their study, thresholds ranged from several
hundreds ns to several ms. They argued that the detectability
of jitter would depend on the contents of materials.
Benjamin and Gannon [1] reported that the thresholds
for jitter on program materials ranged from 30 ns to 300 ns.
The threshold values in their study were a little bit smaller
than those in the present study. It may be attributed to
several differences in the methods.
In the study of Benjamin and Gannon, they connected
the output of the CD player to a distribution amplifier with
two outputs. The first output was connected to a DAC via
an AB comparator box. The second output from the
distribution amplifier was connected to a jitter modulator
that could add jitter by using a function generator as the
jitter source. The output from the jitter modulator was
connected to the DAC via the AB comparator box. Two
signals to be compared were, therefore, from the same CD
player but had different pathways. This might result in a
slight change of sound quality. In the present study, two
versions of the material were reproduced completely in the
same manner without using special equipment.
Secondly, Benjamin and Gannon used sinusoidal jitter
instead of random jitter. They, furthermore, selected the
jitter frequency that might result in detectable distortions
based on observed spectra of the signals. Jitter frequency
they used ranged between 1,530 Hz and 1,850 Hz. Loudspeakers
were used in the most cases in the present study
while Benjamin and Gannon used headphones.
Another difference which is supposed to be most
important is that in Benjamin and Gannons study, the
listeners were allowed to decide their thresholds at their
own discretion. The listeners were asked to adjust the jitter
level until they decided that their thresholds were reached.
The reliability of their own decision was not verified. This
self-administered threshold estimation might allow underestimation
of the threshold values. In the present study,
thresholds were determined objectively based on the scores
in a 2 alternative forced choice paradigm where the
listeners could not determine their thresholds at thei
discretion.
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. According to Benjamin and Gannon,
sinusoidal jitter as small as 30 ns (r.m.s.) might be
detectable under a certain condition. Considering these
results, the maximum acceptable size of jitter would be the
order of ns.
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 [3]. This is way
below the detection threshold values. Nishimura and
Koizumi [6,7] 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.
So far, actual jitter in consumer products seems to be
too small to be detected at least for reproduction of music
signals. It is not clear, however, if detection thresholds
obtained in the present study would really represent the
limit of auditory resolution or it would be limited by
resolution of equipment. Distortions due to very small jitter
may be smaller than distortions due to non-linear characteristics
of loudspeakers. Ashihara and Kiryu [8] evaluated
linearity of loudspeaker and headphones. According to
their observation, headphones seem to be more preferable
to produce sufficient sound pressure at the ear drums with
smaller distortions than loudspeakers.
4. 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"
-k
http://www.jstage.jst.go.jp/article/ast/26/1/50/_pdf
"
Abstract:
Detection threshold for distortions due to time jitter was measured in a 2 alternative
forced choice paradigm with switching sounds. Music signals with random jitter were simulated
digital domain. The size of jitter was arbitrary controlled so that the detection threshold could
estimated. Professional audio engineers, sound engineers, audio critics and semi-professional
musicians participated as listeners. The listeners were allowed to use their own listening environments
and their favorite sound materials. It was shown that the detection threshold for random jitter
several hundreds ns for well-trained listeners under their preferable listening conditions.
...
When the jitter size was 2 ms (r.m.s.), all listeners
scored more than 75% correct. About 25% of the listeners
detected jitter when its size was 500 ns. When it was
250 ns, however, no listener could discriminate the sounds.
The thresholds for random jitter added to program
materials seem to be several hundreds ns. Ashihara and
Kiryu [3] measured detection thresholds for random jitter
in a fixed listening condition. 14 listeners without special
training participated. Some listeners could detect jitter of
1,152 ns but no one detected jitter of 576 ns in their study.
Even though they used a fixed condition and nonprofessional
listeners, their result is comparable to the
present result. Tomizawa et al. [5] measured detection
threshold for artificial jitter under the headphone listening
condition. In their study, thresholds ranged from several
hundreds ns to several ms. They argued that the detectability
of jitter would depend on the contents of materials.
Benjamin and Gannon [1] reported that the thresholds
for jitter on program materials ranged from 30 ns to 300 ns.
The threshold values in their study were a little bit smaller
than those in the present study. It may be attributed to
several differences in the methods.
In the study of Benjamin and Gannon, they connected
the output of the CD player to a distribution amplifier with
two outputs. The first output was connected to a DAC via
an AB comparator box. The second output from the
distribution amplifier was connected to a jitter modulator
that could add jitter by using a function generator as the
jitter source. The output from the jitter modulator was
connected to the DAC via the AB comparator box. Two
signals to be compared were, therefore, from the same CD
player but had different pathways. This might result in a
slight change of sound quality. In the present study, two
versions of the material were reproduced completely in the
same manner without using special equipment.
Secondly, Benjamin and Gannon used sinusoidal jitter
instead of random jitter. They, furthermore, selected the
jitter frequency that might result in detectable distortions
based on observed spectra of the signals. Jitter frequency
they used ranged between 1,530 Hz and 1,850 Hz. Loudspeakers
were used in the most cases in the present study
while Benjamin and Gannon used headphones.
Another difference which is supposed to be most
important is that in Benjamin and Gannons study, the
listeners were allowed to decide their thresholds at their
own discretion. The listeners were asked to adjust the jitter
level until they decided that their thresholds were reached.
The reliability of their own decision was not verified. This
self-administered threshold estimation might allow underestimation
of the threshold values. In the present study,
thresholds were determined objectively based on the scores
in a 2 alternative forced choice paradigm where the
listeners could not determine their thresholds at thei
discretion.
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. According to Benjamin and Gannon,
sinusoidal jitter as small as 30 ns (r.m.s.) might be
detectable under a certain condition. Considering these
results, the maximum acceptable size of jitter would be the
order of ns.
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 [3]. This is way
below the detection threshold values. Nishimura and
Koizumi [6,7] 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.
So far, actual jitter in consumer products seems to be
too small to be detected at least for reproduction of music
signals. It is not clear, however, if detection thresholds
obtained in the present study would really represent the
limit of auditory resolution or it would be limited by
resolution of equipment. Distortions due to very small jitter
may be smaller than distortions due to non-linear characteristics
of loudspeakers. Ashihara and Kiryu [8] evaluated
linearity of loudspeaker and headphones. According to
their observation, headphones seem to be more preferable
to produce sufficient sound pressure at the ear drums with
smaller distortions than loudspeakers.
4. 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"
-k
