"John Phillips" wrote in message
...
On 2007-05-23, Serge Auckland wrote:

"Steve Swift" wrote in message
...

What plausible causes exist for the audio being different when the
individual bits being read off the CD are not? They may arrive with
subtly
differing timings, but the sequence is identical. I'm sure the timing of
the bits varies every time a CD is played, due to varying rotational
speeds of the CD.

If you can do a double-blind test, and he can do this reliably, then you
have something. The only mechanism I can think of that could *possibly*
account for sonic differences is if the copy is so poorly burnt that the
CD
player has a hard time reading the disc and there's a lot of
interpolation
going on. It would then be useful to repeat the DBT using another CD
player
of competely different type to see if the same results are obtained.
Otherwise, two bit-identical CDs will necessarily sound the same.

A common audiophile postulate for audibility of different discs of
nominally identical material is "jitter".

This surprises me a little, having looked at some AES papers on the
audibility thresholds for jitter. Although the research does says that
audible jitter at 10 kHz and above is remarkably low.

Also it seems to me that the jitter hypothesis relies on inadequate
engineering of clock extraction circuits to allow enough jitter to get
through to the audio output. Quite possible I suppose, but eminently
curable (and should not happen in the first place).

--
John Phillips

Quite so! There's no excuse these days for jitter. However, this doesn't
seem to have got through to some designers of "audiophile" DACs. One DAC I
saw reviewed (I can't remember which one but it was expensive!) made the
comment that it was so sensitive, it would reveal the differences between
digital cables. What this meant was that it had such an appallingly
engineered receiver that there was no reclocking of data, and pattern jitter
on the cable went uncorrected. So much for "so sensitive", crap actually.

S.

--
http://audiopages.googlepages.com

In article , Don Pearce
wrote:
On Wed, 23 May 2007 17:27:25 +0100, Steve Swift
wrote:

I probably know more about how CD's work than 99.99% of the population
since my honours degree in Physics contained a generous section on
optics, my secondary subject, Electrical engineering brought me into
daily contact with electronics, my post-graduate work in the Physics
department at Birmingham University and the Rutherford Laboratory in
Oxfordshire included daily use of lasers. I've owned CD players since
1982 (when the biggest problem was finding a CD, let alone knowing how
they worked).

But then what do I know? I'm just a Physicist with an electronics hobby.

I simply don't believe you. Nobody who understands how CDs work would
have written what you did. Were you asleep in class?

Actually, now I read more closely what you have just written, none of
that would of itself give you any insight into how CDs work. Optics
doesn't do it, Electrics doesn't do it and lasers don't do it. Digital
signal processing and audio are the disciplines relevant to the case.

Well, an understanding of lasers and some parts of optics would help with
understanding how the physical data patterns are tracked and read. So they
are relevant, but far from being all that is required.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In article , John Phillips
wrote:

A common audiophile postulate for audibility of different discs of
nominally identical material is "jitter".

This surprises me a little, having looked at some AES papers on the
audibility thresholds for jitter. Although the research does says that
audible jitter at 10 kHz and above is remarkably low.

Also it seems to me that the jitter hypothesis relies on inadequate
engineering of clock extraction circuits to allow enough jitter to get
through to the audio output. Quite possible I suppose, but eminently
curable (and should not happen in the first place).

I may be wrong, but it is my impression that 'jitter' is falling out of
fashion as a 'reason' for the comments made about the 'sound' of players.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

In article , Serge Auckland
wrote:


One DAC I saw reviewed (I can't remember which one but it was
expensive!) made the comment that it was so sensitive, it would reveal
the differences between digital cables. What this meant was that it had
such an appallingly engineered receiver that there was no reclocking of
data, and pattern jitter on the cable went uncorrected. So much for "so
sensitive", crap actually.

It *was* 'sensitive' - the problem was that it shouldn't have been! :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

"Steve Swift" wrote in message


My brother-in-law claims to be able to hear the
difference

Testible with blind, level-matched, time-synched tests. If he obtains the
above opinion in a sighted evaluation, or one that is not properly
time-matched, then he is reporting a difference that is an artifact of his
crappy evaluation method.

between the original and the copy, but only
when the copy was written at greater than 4x speed.

Possible, if you have a CD player that is unduely sensitive to playing
CD-Rs.

What plausible causes exist for the audio being different
when the individual bits being read off the CD are not?

The data being read off the CD have two properties - the binary status of
the bits, and the timing of the bits. The CD player is supposed to address
all relevant issues related to both. So, if the CD player is defective, the
bits could be the same, the timing could be different, and an audible
difference might result.

They may arrive with subtly differing timings, but the
sequence is identical. I'm sure the timing of the bits
varies every time a CD is played, due to varying
rotational speeds of the CD.

The timing changes you suggest are routine and well-known.

The CD player has a lot of circuitry in it to make the timing right again.

"Arny Krueger" wrote in message
. ..
"Steve Swift" wrote in message




The CD player has a lot of circuitry in it to make the timing right again.
Also don't forget "Error Correction" kicking in.

Cheers TT

Don Pearce wrote:
On Wed, 23 May 2007 17:27:25 +0100, Steve Swift
wrote:

Test him, and see if he is right. Then, if you have something
concrete to report come back and there will be something to talk
about. Everything technical you have written above tells us no more
than that you don't know how CDs work.

I probably know more about how CD's work than 99.99% of the
population since my honours degree in Physics contained a generous
section on optics, my secondary subject, Electrical engineering
brought me into daily contact with electronics, my post-graduate
work in the Physics department at Birmingham University and the
Rutherford Laboratory in Oxfordshire included daily use of lasers.
I've owned CD players since 1982 (when the biggest problem was
finding a CD, let alone knowing how they worked).

But then what do I know? I'm just a Physicist with an electronics
hobby.

I simply don't believe you. Nobody who understands how CDs work would
have written what you did. Were you asleep in class?

Actually, now I read more closely what you have just written, none of
that would of itself give you any insight into how CDs work. Optics
doesn't do it, Electrics doesn't do it and lasers don't do it. Digital
signal processing and audio are the disciplines relevant to the case.

d

I think the op was looking for an excuse to wave his credentials in the air.
The opening statement "I probably know more......" did it for me.
Just the sort of bloke you'd love to meet down the pub.

--
Cheerz - Brownz
http://www.brownz.org/

On Thu, 24 May 2007 14:24:20 +0100, "Brownz @ Work"
wrote:

Don Pearce wrote:
On Wed, 23 May 2007 17:27:25 +0100, Steve Swift
wrote:

Test him, and see if he is right. Then, if you have something
concrete to report come back and there will be something to talk
about. Everything technical you have written above tells us no more
than that you don't know how CDs work.

I probably know more about how CD's work than 99.99% of the
population since my honours degree in Physics contained a generous
section on optics, my secondary subject, Electrical engineering
brought me into daily contact with electronics, my post-graduate
work in the Physics department at Birmingham University and the
Rutherford Laboratory in Oxfordshire included daily use of lasers.
I've owned CD players since 1982 (when the biggest problem was
finding a CD, let alone knowing how they worked).

But then what do I know? I'm just a Physicist with an electronics
hobby.

I simply don't believe you. Nobody who understands how CDs work would
have written what you did. Were you asleep in class?

Actually, now I read more closely what you have just written, none of
that would of itself give you any insight into how CDs work. Optics
doesn't do it, Electrics doesn't do it and lasers don't do it. Digital
signal processing and audio are the disciplines relevant to the case.

d

I think the op was looking for an excuse to wave his credentials in the air.
The opening statement "I probably know more......" did it for me.
Just the sort of bloke you'd love to meet down the pub.

Yup, I think you are right.

d

--
Pearce Consulting
http://www.pearce.uk.com

On Thu, 24 May 2007 08:56:32 +0100, Jim Lesurf
wrote:

In article , Don Pearce
wrote:
On Wed, 23 May 2007 17:27:25 +0100, Steve Swift
wrote:

I probably know more about how CD's work than 99.99% of the population
since my honours degree in Physics contained a generous section on
optics, my secondary subject, Electrical engineering brought me into
daily contact with electronics, my post-graduate work in the Physics
department at Birmingham University and the Rutherford Laboratory in
Oxfordshire included daily use of lasers. I've owned CD players since
1982 (when the biggest problem was finding a CD, let alone knowing how
they worked).

But then what do I know? I'm just a Physicist with an electronics hobby.

I simply don't believe you. Nobody who understands how CDs work would
have written what you did. Were you asleep in class?

Actually, now I read more closely what you have just written, none of
that would of itself give you any insight into how CDs work. Optics
doesn't do it, Electrics doesn't do it and lasers don't do it. Digital
signal processing and audio are the disciplines relevant to the case.

Well, an understanding of lasers and some parts of optics would help with
understanding how the physical data patterns are tracked and read. So they
are relevant, but far from being all that is required.

Slainte,

Jim

Not really. This is all about what happens to the data once it has
been read from the disc - the mechanism by which it is read has no
bearing.

d

--
Pearce Consulting
http://www.pearce.uk.com

On 2007-05-24, Jim Lesurf wrote:
In article , John Phillips
wrote:

A common audiophile postulate for audibility of different discs of
nominally identical material is "jitter".
...
I may be wrong, but it is my impression that 'jitter' is falling out of
fashion as a 'reason' for the comments made about the 'sound' of players.

Possibly, but not in all quarters. From two different online reviews
in the recent edition of Stereophile (just the first place I looked):

"It is hard to predict the subjective effect of such high
jitter, but a flat, rather uninvolving presentation would be my
suggestion. I do note that Wes Phillips found that the Oppo player
sounded somewhat soft and overripe in the midbass, which is one
consequence of high amounts of random jitter, in my experience."

(http://www.stereophile.com/cdplayers...po/index5.html)

and

"However, both systems indicated some slight spectral spreading of
the central peak in the graph, due to the presence of some random
low-frequency jitter. Paul Miller has conjectured that this produces
a somewhat larger depiction of objects within the soundstage than is
strictly accurate, coupled with a rather laid-back presentation."

(http://www.stereophile.com/cdplayers/507nag/index4.html)

--
John Phillips