How does the ATIP Wobble signal work (electronicly)

vbimport

#1

Hello,

I’ve been searching and reading information on how a cd-rw drive uses the pregroove wobble as a guide to write to a disc.

Most of what I found is patents, there is a little info on wikipedia, but I still do not know certain things.

The reason why I need some help is because I want to burn data to a disc, and capture this wobble signal and any data associated with it.

But I have no idea of how to do this, would a Analogue to Digital converter do the trick?

Ok first of all the optical read head reads the wobble and then seperates it into 2 parts, one is used as a syncronyzation clock, and the other part is fed into a Phase-Lock-circuit (pll), which then converts it into something else, which is then sent to somewhere else?!?

Ok can someone give me a good description of how exactly the wobble is decoded and sent from and to the optical read head.

And is it possible to record the wobble, use it as a fake wobble. I.e use the wobble that I recorded to my pc, instead of the wobble coming off the disc?

Thanks.


#2

The ATIP wobble is at a frequency of 22.05 kHz. If you were to sample it using an A-D capture card, or a signal analyser then you would need to record it at a higher frequency (say 100khz to allow for sampling accuracy of the analogue signal, the higher the more accurate). If you’re purchasing a card get one that can output the signal too so you can play it back and it should have a trigger signal too so you can trigger on something when recording and playing back in order to be at the same place every time.

If I was you, I would go find your wobble signal on the head using an oscilloscope. Then hook up the signal to your capture device. Record it, preferably for a short-ish period (to begin with) at a known trigger point; The trigger point could be a known pattern or a another signal that changes at the correct time.

Build a switching circuit that can allow you to switch the signal from its original source to your new recording (played through the output of your capture card).
This time at the point of the trigger, switch to your playback; then at the end of your recording switch back so the drive can continue as normal. See if the disc works (assuming the drive didn’t balk).

When looking for the wobble signal on your burner (assuming you don’t know which pin it is on already), playing a normal pressed CD should have no signal, a CDR or PSX disc should have a wobble signal - so you can be sure you find it testing with the different discs.