"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.