I tried a little experiment - playing 1kHz test tones from two CD players
into a dual-trace oscilloscope. ( Actually a software 'scope from
http://www.virtins.com )

How do you rate that?...

The results,

MP3 player: 22ppm slow
Pioneer DV696AV: 12ppm slow
Marantz CD273: reference
Pioneer PD8700: 365ppm fast

I don't know which player has the most accurate clock but it is surprising
that my trusty old Pioneer should be so fast, gaining about 1.3 seconds
in an hour. That's possibly why my wife didn't like it. It must be on
the verge of audibility for someone with perfect pitch.

Umm... and what did the scope -reference- to;?....
--
Tony Sayer