Wobble groove drives?

I understand the theory of wobble groove drives, why they use a wobble groove.

What I’d like to ask is if anyone knows precisely how the drive reads the wobble?

The drive will have a standard beam, perpendicular (normal / straight down) to the disc’s surface, for reading the pits in the bottom of the groove. But then how does it ‘see’ the groove wall wobble? Does it have auxillary beams hitting the disc at an angle to read the wall or does it use it use some trick to read the wobble frequency with the same, or another, perpendicular beam?

I’ve looked all over the net and all I’m getting back is “This is what a wobble groove does”.

Thanks!
John

I know I’m digging this thread up from the dead, but I was wondering the exact same thing and haven’t found the answer anywhere.

Does anyone know how the wobble is read?

I seem to recall reading this several months ago.

http://adterrasperaspera.com/blog/2006/10/30/how-to-choose-cddvd-archival-media/

If that’s not specific enough, then what you’re really looking for is how tracking itself is performed, I think.

-brendan