P-CAV vs. Z-CLV

[glc650]

While browsing another optical drive forum, I came across an interesting discussion about the two recording methods used today -- P-CAV (Yamaha 16x, 20x, & 24x) and Z-CLV (most 24x+ drives). The topic was burn quality and which produced the best burns. I always thought P-CAV would because there's no zones and thus no gaps, unless of course the buffer underrun system needs to kick in. However, a good point was presented:

just like these Z-CLV gaps "feel wrong", so does constant angular velocity feel "wrong" to me. that means the linear speed is not fixed. when burning, to the pits become "longer" when burning near the outside of the CD because there the linear velocity is higher? same problem with reading? how do they correct for this? changing the frequency of the laser pulses etc? i must admit that this makes me more uncomfortable than the Z-CLV gaps.

plain mathematics: if the angular velocity is fixed, then as the radius increases (near the outside of the disc) the linear velocity increases. v=w*r where v=linear velocity, w=angular velocity, r=radius.
so for example, if when writing a laser pulse lasts a certain fixed length of time, if the linear velocity is higher then this pulse would "strech longer" on the cd. is this compensated in P-CAV technology by shortening the length of the laser pulse?
if so, then this means that in P-CAV technology, where the angular velocity is fixed, then the laser pulses have to become shorter as the writing process continues (radius increases steadily). somehow the thought of this makes me uncomfortable.
conversely when reading, again i'm assuming the the "pits" etc. on the cd are of fixed length (am i right?) then as the reading continues and radius increases, since angular velocity is fixed this means that they pass under the pickup for shorter lengths of time. is this problematic?

Any thoughts? Can anyone expand on this?

TIA>

 

[glc650]

Thanks for the reply...

And regarding disks where total accuracy counts (audio) setting the speed to no more than 16X (or 12X, as I tend to do) makes again the whole issue irrelevant.

Yeah, I've heard that people do that. But how about 20x for those 40x drives that support 20x CLV?

 

[Shadey]

Like you said, most drives when writing to a CD-R is normally done using Constant Linear Veloity (CLV) method.

With CLV, the disc rotation speed will be adjusted as to keep a constant data transfer at all portions of the disc. This means the disc rotation speed varies.

The Constant Angular Velocity (CAV) uses a constant disc rotation speed for all portions of the disc, so that the data transfer rates will vary. This method can increase the data transfer rate with minimum load to the drives mechanism.

From what Yamaha says - if you do get gaps - ie from burn proof / safe burn CAV apparently make significantly smaller gaps than CLV.

The Yamahas use Partial CAV (P-CAV) for burns at x20 and faster, CAV used on the inner portions, and CLV used on the outer portions. But full CAV mode is used burning at x4-x12. Well this certainly applies to the 2200 series.

 

[glc650]

Thanks for the reply Shadey...

Since P-CAV burners switch to CLV near the center/outside of the disc, the theory that I quoted above isn't valid because the the drive isn't using CAV on the center/outside tracks, correct?

Also, both P-CAV and Z-CLV burners will use CLV exclusively when a certain speed and below is selected. For example, the Yamaha 24x burner will use CLV throughout the burn when 16x or below is the selected recording speed. As for Z-CLV burners, most 40x drives will use CLV throught when burning at 20x and below. I don't see how recording at CLV throughout would be any different quality wise than when P-CAV or Z-CLV (aside from the gaps between linked zones) is used.

 

[Shadey]

Originally posted by glc650
Since P-CAV burners switch to CLV near the center/outside of the disc, the theory that I quoted above isn't valid because the the drive isn't using CAV on the center/outside tracks, correct?

The mathematics theory *ahem* - it sounds reasonable enough .
But I think they can still gain higher speeds with full cav. The fact that the 2200 only uses full CAV upto and below x12 and uses CLV at 20 speeds on the outer regions of the disc, doesnt necessarily suggest that full cav cannot achieve it also (maybe they deliberately limited the released technology to release it as a better model later). But yet again it could be using CLV because it cant achieve it. We'd just have to wait and see if Yamaha uses full cav beyond x20. Best to read up on the 3200 series.
So personally i cant really comment on that theory as yet.

Also, both P-CAV and Z-CLV burners will use CLV exclusively when a certain speed and below is selected. For example, the Yamaha 24x burner will use CLV throughout the burn when 16x or below is the selected recording speed. As for Z-CLV burners, most 40x drives will use CLV throught when burning at 20x and below. I don't see how recording at CLV throughout would be any different quality wise than when P-CAV or Z-CLV (aside from the gaps between linked zones) is used.

Well I think gapless is better than having gaps, right?

With Z-CLV x24 drives - to burn at x24 you will always get gaps because the method splits the disc into 3 zones, and between the zones there is a speed change. Zone 1 (inner sections) x16, Zone 2 (middle section) x20, Zone 3 (outter section) x24. To achieve the speed changes it relies on burnproof (so there will be gaps). By halting burn, change speed, continue burn, betwwen zones.

With full CAV if you dont get a buffer underrun stopped by burn proof - you can achieve gapless burns.

Usually people suggest to burn at lower speeds for a better quality burn, right? So That means that the CAV will give better quality when burning on the inner sections of the disc than using CLV, because the disc spins slower during the inner sections using CAV than it is using CLV.

I suggest to read this to get a better idea of how it works .
_http://www.cdrinfo.com/articles/pcav-zclv/index.shtml