I know this is probably holy war territory, but I'm hoping for some
interesting ideas.

Starting with an audio CD I can take a "bitwise" image, using something
like Nero. I can then write that image to a writeable CD. I can take a
bitwise image from the writeable CD and compare it to the bitwise image
taken from the original CD. They are identical (with the possible
exception of a time stamp inserted in the image).

My brother-in-law claims to be able to hear the difference between the
original and the copy, but only when the copy was written at greater
than 4x speed.

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.

--
Steve Swift
http://www.swiftys.org.uk/swifty.html
http://www.ringers.org.uk

On Wed, 23 May 2007 15:30:19 +0100, Steve Swift
wrote:

I know this is probably holy war territory, but I'm hoping for some
interesting ideas.

Starting with an audio CD I can take a "bitwise" image, using something
like Nero. I can then write that image to a writeable CD. I can take a
bitwise image from the writeable CD and compare it to the bitwise image
taken from the original CD. They are identical (with the possible
exception of a time stamp inserted in the image).

My brother-in-law claims to be able to hear the difference between the
original and the copy, but only when the copy was written at greater
than 4x speed.

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.

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.

d

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

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.

--
Steve Swift
http://www.swiftys.org.uk/swifty.html
http://www.ringers.org.uk

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

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

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

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

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 Wed, 23 May 2007 15:30:19 +0100, Steve Swift
wrote:

My brother-in-law claims to be able to hear the difference between the
original and the copy, but only when the copy was written at greater
than 4x speed.

And can he perform this test reliably?

"Steve Swift" wrote in message
...
I know this is probably holy war territory, but I'm hoping for some
interesting ideas.

Starting with an audio CD I can take a "bitwise" image, using something
like Nero. I can then write that image to a writeable CD. I can take a
bitwise image from the writeable CD and compare it to the bitwise image
taken from the original CD. They are identical (with the possible
exception of a time stamp inserted in the image).

My brother-in-law claims to be able to hear the difference between the
original and the copy, but only when the copy was written at greater than
4x speed.

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.

--
Steve Swift
http://www.swiftys.org.uk/swifty.html
http://www.ringers.org.uk

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.

S.

--
http://audiopages.googlepages.com