PCAV vs. ZCLV Recording Technlogies - Printer Friendly version

Appeared on: Monday, February 18, 2002
PCAV vs. ZCLV Recording Technlogies

1. Introduction

Partial-CAV versus Zone-CLV - Page 1

- Introduction

CD recorder manufacturers seeking to achieve ultra high writing speeds have been constantly developing new techniques, enhancing older ones and applying any sort of tweaking to their drives. Sanyo was the first company that announced a Zone-Constant Linear Velocity (Z-CLV) recorder. The only other manufacturer who has developed a rivaling technology is Yamaha, with Partial Constant Angular Velocity (P-CAV).

As most readers of this review might be aware off, the original CD reading and recording standards called for the laser beam to follow a spiral movement of constant velocity under the track pits (the 1's and 0's). Hence, until recently, all recorders used to record these "pits" using the CLV (Constant Linear Velocity) method.

Things, however, have drastically changed recently. New recording technologies have been introduced: Z-CLV and P-CAV respectively.

CD recording fans are expected to ask: What are them? How can they be compared against each other? Which technology is faster/better? So, let's find out. We start our journey into some of the more esoteric aspects of recording. Follow us :-)

- Zone-CLV writing technology

Zone-CLV (Constant Linear Velocity) is the recording method being in use lately by many End-drive manufacturers in order to achieve a higher recording speed. All previous recorders used CLV (constant linear velocity) as the main recording method. The rotation speed, in the inside, of a disc at 16x recording speed reaches up to 8000rpm! The high rotation causes problems on the recorder's mechanism and produces loud noise. Sanyo pioneered the development of the Zone-CLV recording method trying to overcome the above two problems by making use of the latest available manufacturing technologies. When a recorder utilizes the current implementation of the Z-CLV recording method, the CD surface is divided into exactly 3 zones. In each one of these zones, starting from the inner to the outer parts of the CD, the recording speed varies.

As you can see in the left picture, the recording speed at zone-1 (inner part of the disc) is 16x, it then increases throughout zone-2 (at exactly time t1) at 20x and finally reaches an 24x-recording speed at zone-3 (after time t2).

A very interesting (and important) question then arises: how can the drive change instantaneously its motor speed? How can it adapt the laser-beam power and continue writing without actually destroying the disk? The question is indeed very simple: BURN-Proof!!!

This technology (or some other of its rivaling variants) can be used for executing the necessary synchronization between adjacent zones (Zone-1/Zone-2 and Zone-2/Zone-3 in this case). There is no imperceptible gap between the various Zones, at least this is what Sanyo states. (How about testing this claim? Read on and you will be certainly rewarded…)

- P-CAV writing technology

In contrast to the Z-CLV recording technology, the P-CAV method keeps the disc rotation constant in the inner portion of the disc and then it gradually lets it drop down as the laser beam reaches a certain predefined distance from the center of it.. In this scenario the actual linear writing speed smoothly accelerates outwards, until it reaches a top limit. After this point, the writing speed is kept constant (CLV) until the end of the recording phase, as it was done in the past.

This new recording methodology has been developed by Yamaha and has been implemented in all its latest drive models. It is known that at the outer part of a disc there can be recorded 2.5 as many bits as in the inner part of it. Simple arithmetic states that during CLV recording the speed is consequently reduced 2.5 times in the outer part. Conversely, in Full-CAV mode (under a constant motor rotating speed) recording speed should be 2.5 times faster in the outer part.

In the current Yamaha implementation of the P-CAV method, the rotation speed is kept moderate (5500 rpm) in the inner portion of the disc. Compare this with the Z-CLV method where the disc spins at over 9000rpm in the inner part. This helps towards achieving an improved recording quality in the inner portion of the disc. This is due to the fact that a moderate disc rotation reduces the vibration that usually is the sole responsible for corrupting quality during this recording phase.

Moreover, as the rotation speed is kept low, the life of both the laser diode and the drive's pickup mechanism is expected to be extended. If Yamaha had allowed full-CAV, the recording speed would have easily reached 30x! So expect more speedy drives in the immediate future from this manufacturer.

- P-CAV vs. Z-CLV

The Z-CLV recording method of Sanyo utilizes the existing CLV method combined with linking technology developed (and in this case exclusively used) for buffer underrun protection. The writing of a disc is divided into several zones, and the writing speed is kept constant within each zone. When it shifts up to the next speed level, writing is suspended and then restarted using the buffer underrun protection.

You can easily see that small gaps are silently being introduced during this recording method. Hence some objections are raised by other laser manufacturers.

Specifically, Yamaha claims that the P-CAV technology is ideal for Audio CDs and pre-mastering a disc for mass duplication, since no links are produced. Other manufacturers say that Z-CLV doesn't affect writing quality since the link is kept very small, almost down to zero. Of course a disc without any links , in theory will have better quality than with links, however small these are.

But can this proved in real life?

- Tested drives

Yamaha 2200E firmware 1.0C
Sanyo CRD-BP1500P firmware vHg.35
Acer CRW2010 firmware vH.KF
LiteOn LTR-24102B firmware v5S.04
PleXWriter PX-W2410A firmware v1.00
Ricoh MP7200 firmware v1.30
Ricoh MP9200 firmware v1.00

- Tested Media

Ricoh 74min 24x Serial Number: C301R1XXXXXXXXXXX
ATIP start of lead in: -02:32:09 (sector: -11409)
ATIP start of lead out: 74:12:00 (sector: 333900)
Manufacturer code: 97 27 66 - Ricoh Company Limited (Type: 6)
Disc subtype: Medium Type C, low Beta category (C-)
Target writing power: 4

- Testing lab

Digital Drives

2. World Of Error Correction

Partial-CAV versus Zone-CLV - Page 2

World Of Error Correction

- What is CIRC?

CIRC (Cross Interleaved Reed-Solomon Code) is the error detection and correction technique used on a CD (and on DVD for that matter). It is a variant of the more general BNC codes. These codes are actually Bytes added during premastering or recording to the normal data bytes for achieving error free reading of a disc. The CIRC bytes are present in all CD modes (audio and data alike). The whole error correction method that makes use of these added CIRC bytes is commonly referred to as the CIRC based algorithm. While the laser head reads the bits out of the disk surface introducing one erroneous bit out of 10^6, the basic level of error correction provided for the Audio CD by CIRC results to only one unrecoverable bit out of every 10^9 bits read! CD-ROM provides additional protection for data (ECC/EDC), the so-called layer 3 (L3) error correction, reducing this error rate to just one bit out of 10^12 bits!

Let's see how this is important. One data bit corresponds to 3.0625 so-called "channel bits". These are the ones that are actually recorded onto a disc surface. A whole disk is 333,000 sectors long. Each sector contains 2,048 data bytes. By performing the necessary simple arithmetic calculations, we can easily see that every data disk would be unreadable without the implementation of both the above error correcting codes.

- How CIRC works?

CIRC uses two distinct techniques in order to achieve this remarkable ability to detect and correct erroneous bytes. The first is redundancy. This means that extra data is added, which offers an extra chance for reading it. For instance, if all data were recorded twice, you would have twice as good a chance of recovering the correct data. The CIRC has a redundancy of about 25%; that is, it adds about 25% additional data. This extra data is cleverly used to record information about the original data, from which it is possible the missing information to be deduced.
(For simplicity, in our explanation throughout this presentation, we silently ignore the 8 to 14, EFM, modulation. In a rigorous discussion of any CD related subject, this should be seriously taken into account.)

The other technique used during the implementation of CIRC is interleaving. This means that the data is distributed over a relatively large physical area of the disk. If the data were recorded sequentially, a small defect could easily wipe out an entire word (byte). With CIRC, the bits are interleaved before recording, and de-interleaved during playback. One data block (frame) of 24 data bytes is distributed over 109 adjacent blocks. To destroy one byte, you would have to destroy these other bytes. With scratches, dust, fingerprints, and even holes in the disc, there is usually enough data left to reconstruct any data bytes that have been damaged or caused the disk to become unreadable.

What happens is that the bits of individual words are mixed up and distributed over many words. Now, to completely obliterate a single byte, you have to wipe out a large area. Using this scheme, local defects destroy only small parts of many words, and there is (hopefully) always enough left of each sample to reconstruct it. To completely wipe out a data block would require a hole in the disc of about 2 mm in diameter.

Moreover, the Reed-Solomon codes used for both levels of error correction are specifically designed for cutting-off "burst" errors, not just those systematic ones that usually come in the form of random errors, the so called Gaussian or white noise.

- What are C1/C2 errors?

The CIRC error correction used in CD players uses two stages of error correction called C1 and C2, with de-interleaving of the data between the stages. The error correction chip in the reading unit can correct two bad symbols per block in the first stage (C1) and up to four bad symbols per block in the second stage (C2). The C1 level of CIRC is meant to correct small, random errors. The C2 level corrects larger errors and burst errors.

- How high/low those values must be?

The lowest as possible! C1 errors cannot be ever zero (0), due to the various media asymmetries, physical defects, fingerprints, dust, etc. C2 errors also must be zero (0), or else you will have reading problems in most CD-ROMs.

The "Red Book" specification (IEC 908) calls for a maximum of 220 C1 errors per second averaged over ten seconds. Discs with higher C1 values are more likely to produce uncorrectable errors. Nowadays, the best discs have an average measurable value of C1 below 10. A low C1 value shows that the system as a whole is performing well, and the pit geometry is good. A peak of 100 bad data blocks per second is acceptable for a CD-ROM, but an average C1 value of 50 per second over the entire disc is a good cutoff point to ensure data integrity.

- Are C1/C2 errors a good indicator about the written media condition?

Yes. We would say that by more than a 80% chance, a disc with low measured C1/C2 error values will have great compatibility among various CD/DVD-ROMS/CD-RW drives.

- What can cause C1 error?

C1 errors can be caused due to physical problems (disk/drive asymmetries, dust, fingerprints) and the writing technology/strategy of each specific recorder. Each manufacturer has it's own writing strategy for achieving the maximum writing speed along with an acceptable writing quality (low error rate). Each drive has "prepackaged" in its firmware a set or orders on how to perform a specific writing strategy with each specific media. For this reason all recordable media are categorized. Each drive reads these codes and adjusts its recording strategy accordingly. Many times the writing quality can be improved with a newer firmware update. C1 errors can also be produced when you don't proper store your burned media.

- What is Writing Strategy?

Proper phase-change recording (that is re-writing), as well as amorphous recording, demands a sophisticated write-strategy, that accounts for the physical properties of the disc (e.g. thermal conductivity). The essential part of every pulse-width-recording method is the use of a multi-pulse write-strategy. All this means that not all 0's and 1's are of equal length when recorded on a disk's surface! The writing strategy takes (or should take) into account all three parameters: drive, disk and data, and perform an optimized laser power adjustment according to predetermined empirical evidence.

- How i can prevent C1/C2 errors?

You must keep your media closed in a jewel case in order to prevent dust and physical damage. Also there is the possibility that your disc can be scratched during insertion/ejection from a drive. This might cause C1 or, even worse, C2 errors.

And, of course, always choose best quality media! (Don't forget, cheaper is not always worse, nor the reverse of this statements holds in all cases.)

- What are the possible causes for a C2 error?

C2 errors are caused either from large media defects, a not properly defined writing strategy, or a soon-to-die laser diode. Overburning is another cause of C2 errors. As you know overburning is not officially supported from any CD standard. Therefore both media and drives are not manufactured to support overburning and this fact alone can cause C2 errors. Where? In the overburned part of a disk of course. The media quality at this point is not as well prepared to perform well as in the rest of the disc, and the drive probably will not be able to burn it properly either. Scratches can also occur when you are NOT carefully placing a burned CD in the tray or throw it from some height, especially over a rough surface.

3. Ricoh 74min 24x Test Results

Partial-CAV verus Zone-CLV - Page 3

Ricoh 74min 24x Test Results

We used the latest 20x and 24x recorders from various manufacturers in order to see how they perform with specific media brands under their maximum speeds. All CDs burned with Nero 5.5.3.5 and were Audio CDs with 74:51:27 lengh size.

- Test Results

In order to simplify the results we have gathered them in the following table:

20x writing speed

Model

C1

Average Burning Time (secs)

Max

Average

Acer CRW2010

47

8,2

314

LiteOn LTR-24102B

38

2,8

280

Plextor PX-W2410A

20

1,9

267

Ricoh MP7200 (JustSpeed On)

39

0,7

277

Ricoh MP7200 (JustSpeed Off)

18

0,5

272

Ricoh MP9200 (JustSpeed on)

18

1,2

290

Ricoh MP9200 (JustSpeed off)

19

2,6

272

Yamaha 2200E (OWC on)

29

0,6

420

Yamaha 2200E (OWC off)

30

1,48

282

As you can see, when recording approaches 20x speed (either P-CAV or Z-CLV), each drive from a different manufacturer gives much different results. In order to have a much more clear opinion about the drive's performance you must study the graphs of the drives (C1 versus Time) that follows in the next pages.

In this test, Ricoh 7200 was the best performer, especially when recording was done with JustSpeed turned off. The drive gave the lower C1 average error value. This should not surprise us, as the tested media comes from Ricoh :-). The drive did performed slightly worse when JustSpeed was turned on, due to a max peak value of 39, which of course also raised the average C1 error rate. So does the Ricoh Mp7200 seem to perform better when JustSpeed is turned off? Yes and No. When the Ricoh drive is tested using the Ricoh 24x media, it seems that the answer is yes, but with media from other manufacturers, it may as well be no. More tests must be carried out in order to be able to reach a definite conclusion.

The Yamaha 2200E seems to also perform very well in our tests. With OWC (Optimum Writing Control) enabled, it gave us slightly higher C1 values than the Ricoh MP7200. With OWC turned off, things are, unfortunately, much worse. It seems the drive is in an urgent need for firmware upgrade in this area :) You will have to spent some more time during burning with this drive, if quality matters for you.

Ricoh MP9200 seems not to be able to perform as well as we expected. The drive gave much higher C1 errors than its MP7200 cousin. Again, JustSpeed should be left on for getting the maximum possible quality.

The Plextor's PX-W2410A PoweRec II system also gave us the unexpected results. Of course, the drive had the lower recording time among the rest of the competition, but (unfortunately) the average C1 errors are also higher.

The LiteOn's 24102B Smart-BURN also doesn't seem to be a front runner when it comes to recorded error rates. The drive had much higher C1 errors than both the Ricoh MP7200 drive and the Yamaha 2200E.

Our last tested drive, the Acer 2010, is not only the slower drive among all, but also gave us the highest C1 error rates in our tests. When the drive changes speed from 16x to 20x, it produces many C1 errors. At the lower 12x and 16x writing speed it seems that it is performing very well.

24x writing speed

Model

C1

Average Burning Time (secs)

Max

Average

LiteOn LTR-24102B

43

2,9

246

Plextor PX-W2410A

31

2,0

240

Sanyo CRD-BP1500P

25

2,7

241

At the 24x Zone-CLV writing method, Plextor's PowerRec II system seems to make the difference from the competition. The Plextor drive not only gave back the lower recording time but also the lower C1 error rate. The Sanyo CRD-BP1500P comes second with a one second higher writing time and a somewhat higher C1 error rate. Last, the LiteOn LTR-24102B offers the higher burning time and C1 error values as well.

4. Ricoh 74min 24x Test Results - Acer CRW2010A

Partial-CAV versus Zone-CLV - Page 4

Ricoh 74min 24x Test Results - Acer CRW2010A

- Test Results

In order to simplify the results we have gathered them in the following table:

As the C1 versus Time graph shows, the Acer CRW2010 shows an unpleasant behavior. After a 37minutes recording, at exactly the point where the speed shifts from 16x CLV to 20X CLV, the drive produces much more errors. From an average of 10 C1 errors, they also shift up to an average of 20-25 per second. Especially towards the end of the disk, the errors are further increased.

5. Ricoh 74min 24x Test Results - LiteOn LTR-24102B

Partial-CAV versus Zone-CLV - Page 5

Ricoh 74min 24x Test Results - LiteOn LTR-24102B

- Test Results

In order to simplify the results we have gathered them in the following table:

As the C1/Time graph shows, the LiteOn LTR-24102B produces a typical C1 error-rate image. The drive starts with a low C1 error rate in the inner part of the disk and as time passes, errors are increased as well. This behavior further deteriorates when the head approaches the exterior part of the disk.

At the 24x writing speed, the LiteOn exhibits a similar image as in the case of 20x recording. This drive produces slightly higher C1 errors during the speed change points located the first at 6 minutes of 1x playback (16x to 20x speed change) and at 14minutes (20x to 24x shift). In the end, C1 errors are going again high.

6. Ricoh 74min 24x Test Results - Plextor PX-W2410A

Partial-CAV versus Zone-CLV - Page 6

Ricoh 74min 24x Test Results - Plextor PX-W2410A

- Test Results

In order to simplify the results we have gathered them in the following table:

At the 20x writing speed, the Plextor drive shows a very "nice" behavior. The drive's C1 overall progress grows constantly and at the end of the disc the errors are somewhat more increased.

24x writing speed

Model

C1

Average Burning Time (secs)

Max

Average

LiteOn LTR-24102B

43

2,9

246

Plextor PX-W2410A

31

2,0

240

Sanyo CRD-BP1500P

25

2,7

241

When writing at 24x speed, the PleXWriter produces a high amount of C1 errors at the first speed change point (5mins in this case) from 16x to 20x, and also a high value at the second speed change point (14minutes) from 20x to 24x. However at the rest of the disc the C1 error rate stays at a relatively low level. It just increases again at the end of the disc.

7. Ricoh 74min 24x Test Results - Ricoh MP7200A

Partial-CAV versus Zone-CLV - Page 7

Ricoh 74min 24x Test Results - Ricoh MP7200A

- Test Results

In order to simplify the results we have gathered them in the following table:

The Ricoh MP7200A drive when recording at 20x with JustSpeed enabled, produced a 0.7 C1 average error rate. The drive produced high error rates at 5mins, which, however, is not the speed change point from 16x to 20x! During the rest of the disc C1 errors seem very small, as most of them are close to 0.

To our surprise, this drive when JustSpeed was disabled produced a better overall image! How can this be possible? It seems that the writing strategy this drive follows in this case is, as expected, more conservative. How about the Ricoh engineers offering a further firmware tweaking?

8. Ricoh 74min 24x Test Results - Ricoh MP9200A

Partial-CAV versus Zone-CLV - Page 8

Ricoh 74min 24x Test Results - Ricoh MP9200A

- Test Results

In order to simplify the results we have gathered them in the following table:

The newer Ricoh MP9200A drive at 20x writing speed with JustSpeed enabled, produced an 1.2 C1 average error rate, which is certainly higher than the MP7200. Remember that the drive's firmware is only 1.00, when MP7200 is shipped with firmware version 1.30! MP7200 seems to be better calibrated, a natural consequence as the model has been in the market from May and records at a slight lower average speed as well, where the optomechanical system is less stressed. This drive's overall image is very good, but in the end, as in all cases tested thus far, the error rate is somewhat high.

The Ricoh MP9200, with JustSpeed disabled, produced higher C1 errors than when JustSpeed was enabled. This is what exactly Ricoh itself claims and it seems to be correct according to our evidence.

9. Ricoh 74min 24x Test Results - Sanyo CRD-BP1500P

Partial-CAV versus Zone-CLV - Page 9

Ricoh 74min 24x Test Results - Sanyo CRD-BP1500P

- Test Results

In order to simplify the results we have gathered them in the following table:

24x writing speed

Model

C1

Average Burning Time (secs)

Max

Average

LiteOn LTR-24102B

43

2,9

246

Plextor PX-W2410A

31

2,0

240

Sanyo CRD-BP1500P

25

2,7

241

Sanyo's 24x proposal seems to perform quite on the average, especially when compared to its Plextor PX-W2410A "rival". This drive's particular weak point is the high C1 error rate just after the position on the disc corresponding to 51 minutes recording time at 1x speed.

10. Ricoh 74min 24x Test Results - Yamaha CRW2200E

Partial-CAV versus Zone-CLV - Page 10

Ricoh 74min 24x Test Results - Yamaha CRW2200E

- Test Results

In order to simplify the results we have gathered them in the following table:

The Yamaha CRW2200E drive exhibited a very good tested recording quality during throughout the entire CD. There seems to be a problem at the position corresponding to 15 minutes 1x recording, since the drive produced a very high error rate at this exactly point! The same effect was also noticed when OWC (Optimum Writing Control) was disabled...

With OWC disabled, Yamaha produced a worse CD recording quality than with OWC turned on. The drive maybe 48% faster in this mode, but also produces a 60% "lower quality" disc. So it is recommended that OWC should be always turned on.

11. Conclusion

Partial-CAV versus Zone-CLV - Page 11

Conclusion

After all these tests, you may still wondering. Which is better? P-CAV or Z-CLV? The answer is not easy. Yamaha 2200E may be producing very good quality CDs, but the Ricoh MP7200A drive has done even better. The Yamaha 2200E model seems to have a problem recording at the "15minutes" area where it produces high error rates, when Ricoh MP7200 seems performing very good throughout the entire disc. Of course, Ricoh manufactures the media which we used for all our tests and maybe this is the cause of this drive being "assigned" itself the first place....

When writing at 24x speed, Plextor's PoweRec II seems to be performing very well and offered not only the lower recording time but also the lower C1 error rate. Please take into account that the error rates at 24x recording speed cannot be compared with those exhibited at 20x. This seems normal since, no recording system can escape from nature's laws.

The subject of our review here is very hot and for sure more tests with many other media and drive combinations will follow in the near future. So, stay tuned! The jurney just started...

20x writing speed
Model	C1		Average Burning Time (secs)
Model	Max	Average	Average Burning Time (secs)
Acer CRW2010	47	8,2	314
LiteOn LTR-24102B	38	2,8	280
Plextor PX-W2410A	20	1,9	267
Ricoh MP7200 (JustSpeed On)	39	0,7	277
Ricoh MP7200 (JustSpeed Off)	18	0,5	272
Ricoh MP9200 (JustSpeed on)	18	1,2	290
Ricoh MP9200 (JustSpeed off)	19	2,6	272
Yamaha 2200E (OWC on)	29	0,6	420
Yamaha 2200E (OWC off)	30	1,48	282

24x writing speed
Model	C1		Average Burning Time (secs)
Model	Max	Average	Average Burning Time (secs)
LiteOn LTR-24102B	43	2,9	246
Plextor PX-W2410A	31	2,0	240
Sanyo CRD-BP1500P	25	2,7	241