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?