Hi NATDBERG,
The reality is, playing a CD sometimes requires short (relatively speaking) speed variations. Some of these are user induced, others due to disc imperfections. No matter what the cause, to deal with these situations you want small servo correction signals or you run the risk of having the servo system "clip" in the same way an audio amplifier can. When this happens the feedback loop is broken and the servo operates at full gain. This "sticks" the output at one rail. This will self correct, but only after the recovery time. During this period the servo applies full, maximum force to the disc in an attempt to correct the error. This often doesn't end well for the electronics and it certainly doesn't help the motors and coils (tracking & focus). This is why some CD servo control circuits apply a mute to the servos - depending on which one when out of bounds. The effect will be felt in the buffer and perhaps downstream from that as well.
Mark has illuminated the core issue for you,
I guess you are thinking along the lines that a light rotating mass will for some reason "hunt" or otherwise be unstable. This would only be a problem in a badly designed CD servo section. Designs like that would have many more "issues" (undocumented features) and you probably wouldn't be looking at them to begin with.
-Chris
Since that issue doesn't pertain to CD transports, I ignored it. Keep on track here
The reality is, playing a CD sometimes requires short (relatively speaking) speed variations. Some of these are user induced, others due to disc imperfections. No matter what the cause, to deal with these situations you want small servo correction signals or you run the risk of having the servo system "clip" in the same way an audio amplifier can. When this happens the feedback loop is broken and the servo operates at full gain. This "sticks" the output at one rail. This will self correct, but only after the recovery time. During this period the servo applies full, maximum force to the disc in an attempt to correct the error. This often doesn't end well for the electronics and it certainly doesn't help the motors and coils (tracking & focus). This is why some CD servo control circuits apply a mute to the servos - depending on which one when out of bounds. The effect will be felt in the buffer and perhaps downstream from that as well.
Mark has illuminated the core issue for you,
Only people without a clear understanding on how the process of reading a CD actually works could get this wrong. It is an argument so basic that there isn't any reason to think along the lines of constant rotational speed.
I guess you are thinking along the lines that a light rotating mass will for some reason "hunt" or otherwise be unstable. This would only be a problem in a badly designed CD servo section. Designs like that would have many more "issues" (undocumented features) and you probably wouldn't be looking at them to begin with.
-Chris
Define "high".
As I say, the CDM0/1 uses a brass flywheel - the angular momentum of that plus the spindle's higher mass construction in the first place must be some hundreds of times larger than say that of a boombox mech.
Low friction is good for constant speed. Don't we want that either?
Depends how a mech controls the speed - surely it actively slows the motor down to reach slower speeds rather than relying on friction and so again is no more than a matter of energy imparted for that control. I don't know the details of the usual servo methods - do they rely soley on friction to decrease speed?
It seems to me you're talking in terms of philosphy and not practical reality. Constant speed may not be what is being aimed for but the speed won't be constant if the servo is amply able to control the angular movement of the drive for a given angular inertia.
Not at all - it's just being repeated whilst kind of not taking in what I'm saying - or at least what I think I'm saying. I'm obviously not communicating the point well enough..
I'm not thinking that and I have said several times that I'm not thinking that. I would only be adding mass to a design in order to clamp the CD in some way to make non-perfect CDs closer to flat - all that lifting in and out of cases can and does cause imperfections which then the laser has to go about refocusing for. Or to aid reading of a CD in a bad environment like the VRDS can do (presume because of the VRDS) - although in this case for home use it won't be an issue worth dealing with.
But the argument I'm hearing is that adding mass is bad BECAUSE we are not looking for constant speed and that a higher mass will cause this.
I'm saying that given a stronger servo mechanism and higher torque motor the ablility to control speed will not be affected.
Hi NATDBERG,
Since that issue doesn't pertain to CD transports, I ignored it. Keep on track here
The reality is, playing a CD sometimes requires short (relatively speaking) speed variations. Some of these are user induced, others due to disc imperfections. No matter what the cause, to deal with these situations you want small servo correction signals or you run the risk of having the servo system "clip" in the same way an audio amplifier can. When this happens the feedback loop is broken and the servo operates at full gain. This "sticks" the output at one rail. This will self correct, but only after the recovery time. During this period the servo applies full, maximum force to the disc in an attempt to correct the error. This often doesn't end well for the electronics and it certainly doesn't help the motors and coils (tracking & focus). This is why some CD servo control circuits apply a mute to the servos - depending on which one when out of bounds. The effect will be felt in the buffer and perhaps downstream from that as well.
-Chris
Thank you !
Now that is a REAL practical and in-depth problem that higher mass can bring along and from the above it looks like you're saying it's really too much effort to build a beefier servo mechanism and is more than simply adding a higher torque motor. That's a good reason to deliberately cut the mass.
Then again... VRDS doesn't seem to have these problems so it is again a matter of magnitude, theory v practical reality.
I guess the fact that my Teac CD701 works perfectly with its platter, its custom motor and has scrub and fine speed control kind of flies in the face of any idea that high mass "doesn't work" . It does work perfectly well thanks! It may go against an idealist philosophy and an idealist CD engineer may not like it because it goes against their own personal design requirements for a good mech but it absolutely does work perfectly well.
But as has been said, it might not be actually doing anything to make it sound any better and is over-engineering for not much benefit other than a bit of marketting.. who knows?
Hi NATDBERG,
What a great mechanism that was! Expensive to replace as well.
-Chris
No. You define high, since you are the one arguing the subject. Please clearly define your set of circumstances.
It also used a brass counterweight on the swing arm. It also used to get broken flex PCB and the lens suspension would sag, trashing the entire mechanism.
What a great mechanism that was! Expensive to replace as well.
Nope. We want constant linear velocity. Friction hasn't anything to do with what type of mechanism, but windage losses sure do!
Then, perhaps you might want to find out before engaging industry experts in your arguments. Please read what has been posted so far as many of your answers can be found there.
Really ! ? We have been "telling it like it is". You can't even argue philosophy because you don't understand how these things actually function. Please, get a grip on reality. Read and learn. Most of the stuff you drag up simply doesn't happen in real life. It could if the design was botched badly enough, but not with good products in the marketplace.
Please educate us on which situation would result in the servo being so lightly damped with too high a gain. These are well known factors in servo design since long before a CD first spun a disc. Honestly, you are insulting our intelligence with the comments you have been making. Get an education and then get some experience. After that you can talk about it. You have been exposed to the answers to these questions, but no uptake has been taking place.
-Chris
Hi NATDBERG,
I have personally serviced those machines as an authorized Tascam service center. I think I can speak from a position of real experience here. Heck, they did pay me for working on them. We took overflow from the Canadian distributor (Teac Canada).
Look, I'm past discussing this with you. As I said before, answers to your questions have been posted. If you want to learn about the finer details, pay for a course. We are not here to train you or argue the facts that we and the entire industry know well.
-Chris
I have personally serviced those machines as an authorized Tascam service center. I think I can speak from a position of real experience here. Heck, they did pay me for working on them. We took overflow from the Canadian distributor (Teac Canada).
Look, I'm past discussing this with you. As I said before, answers to your questions have been posted. If you want to learn about the finer details, pay for a course. We are not here to train you or argue the facts that we and the entire industry know well.
-Chris
Even Lampizator is not a fan of VRDS. The words "plastic crap" are used more than once. Here the flywheel is an injection moulded disc that is probably less flat than a CD. Placing the motor on top is also a challenge as now the disc and clamping device are now hanging on to the underside of the flywheel/motor. No high force clamping possible.
VRDS-T1
Of cause your Teac 701 works. It was designed to do so. And, in some extreme situations like in a club or in a mobile studio it may work better than a standard design. But at what cost. higher mass results in a larger motor, larger bearings, more friction, higher power electronics (servo,PSU) and more ground noise. And, still no increase of the clamping force.
VRDS-T1
Of cause your Teac 701 works. It was designed to do so. And, in some extreme situations like in a club or in a mobile studio it may work better than a standard design. But at what cost. higher mass results in a larger motor, larger bearings, more friction, higher power electronics (servo,PSU) and more ground noise. And, still no increase of the clamping force.
Hello, This is a very informative thread - please go on and focus on the technical details! For me it is clear that the mass of a CD platter does not matter _if_ the motor is strong enough. But it is also clear that in practice this will not always be the case... Anyway it does not matter if the Cd has constant velocity speed or not. Any serious CD player will have a FIFO memory which can store at least a second of data. The DAC reads the data out with a crystal clock from this FIFO. Jitter in CD velocity does therefore not matter and additional mass is not needed. This is also highly desireable if the CD has errors and the player reads the erroneous track a second or third time. If it does not have FIFO memory it can not do this without dropouts.. I know that many here think that the cheap computer players are worthless... but has anyone done some serious tests if this is true? In the comming years this may be the only remaining option and i am very intereseted if it is a good alternative or not. Maybe there are huge quality differences between CD-Rom players? Regards, Udo
Hi Udo,
I have checked the eye pattern before on CDROMS that can read at 52X, but was reading at the proper speed for audio playback. As expected, the eye pattern left a lot to be desired. It is clearly an inferior product which is reflected in the low average cost for these devices.
Many of your other comments are ill informed, but I'll leave it at that.
-Chris
I have checked the eye pattern before on CDROMS that can read at 52X, but was reading at the proper speed for audio playback. As expected, the eye pattern left a lot to be desired. It is clearly an inferior product which is reflected in the low average cost for these devices.
Many of your other comments are ill informed, but I'll leave it at that.
-Chris
There is no "high-end" CDROM drive.
CDROM quality in general is equal with DVD (which is worse than CDP). Memory is a positive thing because data can be read several time and corrected before it is decoded. But the high speed is a very negative thing...
I believe that properly aligned, both CDP or CDROM drive could perform perfectly. But for how long, that's the question. The speed is I believe the major contributor to the failing of the mechanism. No DVD or fast CDROM can live long (but I still have an old 5X CDROM that is still functioning).
Forget about the eye-pattern. Here you can see the results of testing discs using Phillips CD-DA(CD-CATS), Plextor CD-ROM (Datarius) and Plextor CD-DVD (Clover) drives and the computer drives have consistently lower error rates.
http://falconrak.net/wp-content/uploads/518297ed1e86eeac531c3557a4816389.pdf
http://falconrak.net/wp-content/uploads/518297ed1e86eeac531c3557a4816389.pdf
It bothered me that they don't report the consistency of the measurement. Two examples...
One, when they found LG CD writer perform better than Pioneer CD writer, does the LG represent the average writers out there? Or, will LG consistently be better if recording is done twice, thrice, 4x, etc.? (It seems to me that they just wanted a positive result for the CD being tested).
Two, when they found that the DVDROM analyzer performed much better than the CDROM for CD exposed to UV, was it normal such that it didn't require consistency test? Because if the measuring tools are "faulty", so are the results.
Mark, I disagree if the condition where NO PROBLEMS were found with both CDP and DVDROM is used to judge them. Like I said before, when properly aligned (the grating) and new, both can perform perfectly. The difference in error before correction is insignificant and no uncorrected errors found.
But the test showed what happened when the CD lost its reflectivity due to UV (aka aging). The CDROM analyzer suddenly measured horrible performance.
But against bad recording (i.e. using Pioneer writer instead of LG), CD drive seems to report increased errors, especially with data stored at outer diameter. And just like my observation with CD, the song written on the outer track tend to have lower sound quality (my perception and no ABX of course).
And the fact that CDROM and DVDROM perform differently, tells me that it could be just product huge variance. Because I believe that in production, ensuring consistency and accuracy is very costly, such that if you measure jitter (for example) from random players in the market and correlate them with price, you will not get good correlation. Manufacturers just don't have time (money) to ensure that the products are perfect out of QC dept.
Afterall, this was a CD test, NOT a player test. With players, we want consistency after being abused (all-day music, random play, etc). And we want good ability in playing defective CD, as tha test show implicitly that even a new unrecorded disks have limitations.
Then there is the importance of the chipset. Soundwise, my favorite chipset for CDROM based player was from Oak Technology (OTI). This chipset is rarely found in CDROM drives, even tho the company has high contribution in CDROM technology. OTI then owned by Zoran, which happens to be a good chipset provider for DVD (Zoran Vaddis 6 and 7).
Would you get the same results if you used a different make/batch of discs? It just shows the results of this combination of discs and writers. Were they looking for the best writer for this brand of discs?
The measuring tools are not faulty. A disc is read and the errors are counted and reported. There is no calibration possible. The PlextorDVD is just able to read discs at a lower error rate than the other drives.
My interpretation is that even when the Philips/CD-DA does reasonably well, it is still outperformed by the other drives.
A (DVD)drive that can read (marginal) discs at lower error rates. We are seeing evolution at work here.
It would also be interesting to see how the player/drives handle defects like scratches and fingerprints.
i had changed laser in my old 98 sega saturn , now it reads fine but it looks like servo is not doing fine it works and after some 30 seconds - minute it skips. like it cant change speed slowly so it just skip and then continues playing. what to do without scope? i should probably recap it soon . i think it is very good quality made so i would like to fix it. what you people think i should check?
, now it reads fine but it looks like servo is not doing fine it works and after some 30 seconds - minute it skips. like it cant change speed slowly so it just skip and then continues playing. what to do without scope? i should probably recap it soon . i think it is very good quality made so i would like to fix it. what you people think i should check?What is the reason to use data from a good writer and dispose off data from bad writer? This is obviously not a worst case scenario test. I'm more interested to know what happen if the disc is CD-DA of 2 years old of age (and the player/analyzer too)
Repeatability test.
The DVDROM yes, the CDROM not really.
Yes. But the drive might not sufficiently be abused. With music, I play music almost every hour, not to mention skipping tracks. This, along with high rotational speed might ruin the grating alignment.
I have no problem with new DVD drives. When they start to skip tracks, I feel they don't sound as good anymore.
Graphs on page 8 and other data clearly show the error correction per player. Clover reads at lower error rates. You can re test a disc and the results will not change per player.
Are the drives failing because of grating alignment? It would be one of the last things I would be expecting to cause playback problems.
Are the drives failing because of grating alignment? It would be one of the last things I would be expecting to cause playback problems.
I know from observation that DVD and DVDROM do not last long. Currently I have around 20 DVD players. DVDROM? Don't ask.
My best (expensive) DVD players are failing and I start to give up.
CD/VCD mechs have "spring", DVD and DVDROM don't have. DVD mechs require FLAT and non vibrating surface because of this.