This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
This phenomenon is familiar to users who have attempted to extract digital
audio from a CD-R. Very often the result of copying an audio CD is an
exact copy of the original audio data, but with a few hundred zero bytes
inserted at the front (and a corresponding number lost off the end). Since
this represents the addition of perhaps 1/100th of a second of silence at
the start of the disc, it's not really noticeable.
The actual number of bytes inserted may very slightly from disc to disc,
but a given recorder usually inserts about the same number. It's usually
less than one sector (2352 bytes).
According to a message from a Yamaha engineer, the cause of the problem is
the lack of synchronization between the audio data and the subcode
channels, much like the "jitter" described in section (2-15). The same
data flow problems that make it hard to find the start of a block when
reading also make it hard to write the data and identifying information in
sync. According to the engineer, no changes to the firmware or drive
electronics can fix the problem.
Making copies of copies of audio CDs would result in a progressively larger
gap, but it's likely to be unnoticeable even after several generations.