Hi Chris
Talk about C2 errors. Have you ever played with those computer CD-ROM/DVD-ROM drives? There are lots of software tools to check out C1/C2 numbers. Based on my finding, most CDs have lots of C1 errors yet C2 errors are often close to 0, definitely does not look right to me. Based on your statements, I assume that most CD ROM drives would simply shutdown C2 error reports? Yet still I can see C2 errors shown up from the same drive once a while. This really puzzles me.
-finney
Talk about C2 errors. Have you ever played with those computer CD-ROM/DVD-ROM drives? There are lots of software tools to check out C1/C2 numbers. Based on my finding, most CDs have lots of C1 errors yet C2 errors are often close to 0, definitely does not look right to me. Based on your statements, I assume that most CD ROM drives would simply shutdown C2 error reports? Yet still I can see C2 errors shown up from the same drive once a while. This really puzzles me.
-finney
Hiya finney,
CDROM drives will normally reread when they get CRC errors. Something a CD transport is not designed to do. They have substituted rereading for quality and it happens to work. They also happen to wear out quickly if used for normal audio playing. What is truly sad is that the cheaper CD drive we have now in CD players are comparable in quality to a CDROM drive. That was not always the case.
Remember, from a manufacturing standpoint, throw away audio has a ton of benefits. Problem is that we have differed the costs to society at a later date. Cute eh? I strongly disagree with this tactic, because we all will end up paying for this in some way (or many ways).
C2 errors reported in software I would not trust really. Gimme the real flag any day. However, rereading the data may actually reduce the read C2 errors to a minimal amount. Really true on a new drive, not a worn one. Oh, I have not wasted my time with CDROM type drives. Otherwise I would optimize them.
Hi tade,
Hi Karl,
-Chris
CDROM drives will normally reread when they get CRC errors. Something a CD transport is not designed to do. They have substituted rereading for quality and it happens to work. They also happen to wear out quickly if used for normal audio playing. What is truly sad is that the cheaper CD drive we have now in CD players are comparable in quality to a CDROM drive. That was not always the case.
Remember, from a manufacturing standpoint, throw away audio has a ton of benefits. Problem is that we have differed the costs to society at a later date. Cute eh? I strongly disagree with this tactic, because we all will end up paying for this in some way (or many ways).
C2 errors reported in software I would not trust really. Gimme the real flag any day. However, rereading the data may actually reduce the read C2 errors to a minimal amount. Really true on a new drive, not a worn one. Oh, I have not wasted my time with CDROM type drives. Otherwise I would optimize them.
Hi tade,
Sorry, no. Do you notice how open the optics are?? They used to be sealed from dust and airborne contaminants. Is there a heat issue they are trying to solve the cheap way, or is that drive simply really, really cheap. I don't have to guess.
Hi Karl,
Possible. Troubleshoot by substitution. That is the best way. I once made a CD player with an RF test point available to an external 'scope for this exact reason.
Well, that would be more dependent on the chip set and it's implementation. I normally concern myself with stability, how clear it is and the RF envelope level. Then I drop down my horizontal sweep speed and look at the envelope compared to the focus and tracking servo outputs. Trigger on the servo. This allows me to see effects on the RF envelope due to mechanical issues or servo mis adjustment. It helps to look at a population to get a feel for what is normal.
-Chris
Hi Chris
Actually in the test software, you can disable the reread op in CD-ROM drives. This is why it puzzles me so much. Data CDs have different error correction code anyway. Here I am just talking about audio CDs. The near zero C2 rate is simply unbeliveable.
On the other side, since I am burning mostly DVD Audio discs these days. DVD is using the PI and PO encoding. In theory, their strength is not much better than CDs yet in reality they seem to work better than CDs. Data correctness-wise, I actually find out DVD Audio is much more reliable than CD.
-finney
Actually in the test software, you can disable the reread op in CD-ROM drives. This is why it puzzles me so much. Data CDs have different error correction code anyway. Here I am just talking about audio CDs. The near zero C2 rate is simply unbeliveable.
On the other side, since I am burning mostly DVD Audio discs these days. DVD is using the PI and PO encoding. In theory, their strength is not much better than CDs yet in reality they seem to work better than CDs. Data correctness-wise, I actually find out DVD Audio is much more reliable than CD.
-finney
anatech said:
Hello
Why cdrom drives happen to wear out quickly if used for normal audio playing ?
I was think to use my LG GCR-8520B cr rom as a cd drive mechanism.
I did test the jitter looking at it on my fft. I did use burned cd with a 16bit/44.1kHz JTEST signal wave file. Made of a 11025Hz square wave with 229.6875Hz LSB
How come that my LG cd rom as very very low jitter compared to my Denon DCM-420 cd player and my Toshiba SD-2800 DVD player ?
Thank
Gaetan
Here's the jitter of my LG cd rom GCR-8520B
An externally hosted image should be here but it was not working when we last tested it.
Here's the jitter of my Denon DCM-420 cd player
An externally hosted image should be here but it was not working when we last tested it.
Here's the jitter of my Toshiba SD-2800 DVD player
An externally hosted image should be here but it was not working when we last tested it.
Hi gaetan8888,
Depends on the controlling software. CD players read one time only unless they can't track. I have no idea what CDROM drives do.
Things I am talking about have been directly observed by myself over a long period of time. But think about this. How can a more cheaply made item outperform a purpose built item?? It can't, but they may be some tricks it uses. Remember that a real CD transport has but a tiny little ram buffer to use and a CDROM reads quickly and feeds a big buffer.
Your test appears to be like my FFT tests when it is not synced properly, your first one is. There must be an issue with what you are doing here. I'm not going to troubleshoot that, I'd have to do the test with you to see where the problem is.
-Chris
Depends on the controlling software. CD players read one time only unless they can't track. I have no idea what CDROM drives do.
Things I am talking about have been directly observed by myself over a long period of time. But think about this. How can a more cheaply made item outperform a purpose built item?? It can't, but they may be some tricks it uses. Remember that a real CD transport has but a tiny little ram buffer to use and a CDROM reads quickly and feeds a big buffer.
Your test appears to be like my FFT tests when it is not synced properly, your first one is. There must be an issue with what you are doing here. I'm not going to troubleshoot that, I'd have to do the test with you to see where the problem is.
Because at one time they were built much cheaper than real CD player transports. Unfortunately I'm seeing some real trash out there now. Keep in mind that all CD transports wear with time. Disc motor bearings especially. Your computer CDROM is used to load data and programs, so it doesn't make sense to wear it out before you really need it. If you really want to use your CDROM for music, go ahead. Just keep a spare around to swap out. They are cheap enough.
-Chris
Hi Gaetan,
If your sound card is not synced to the signal, or if resampling has occurred, you will get that pattern. This looks more like a test method problem than a transport issue.
There will be zero, or extremely little jitter after the signal runs through a CD machine. The data is clocked in to the ram via a PLL clock, and clocked out using the system clock. From a system standpoint there will be no jitter. It was eliminated by that first step. That is what teh ram is for in the DSP area.
In other words, you can not test for transport jitter without access to the eye pattern. There are rather expensive jitter meters made for this purpose from Leader to Agilent.
In other words, you can not do what you are trying to do and get any realistic answers.
-Chris
If your sound card is not synced to the signal, or if resampling has occurred, you will get that pattern. This looks more like a test method problem than a transport issue.
There will be zero, or extremely little jitter after the signal runs through a CD machine. The data is clocked in to the ram via a PLL clock, and clocked out using the system clock. From a system standpoint there will be no jitter. It was eliminated by that first step. That is what teh ram is for in the DSP area.
In other words, you can not test for transport jitter without access to the eye pattern. There are rather expensive jitter meters made for this purpose from Leader to Agilent.
In other words, you can not do what you are trying to do and get any realistic answers.
-Chris
anatech said:
Hello Chris
Maby replacing my 16 bit soundcard by a pc-scope like the small Velleman kit to see the jitter ?
Is there a web page who explain a simple way to test cd transport jitter by the eye pattern ?
But if I just want to compare few cd player jitter output, if I use my burned cd with the 16bit/44.1kHz JTEST signal wave file, and send the output signal from the cd players to test to my HP-333 and measure the residual signal, by centering the HP-333 on 11025Hz, the more they would be jitter and the more distortion level I would have ?
Thank
Gaetan
Hi Gaetan,
You can measure jitter off the CD by looking at the eye pattern. The amount of horizontal shift is caused by jitter if you are triggering properly, otherwise noise can cause the same effect. The EFM signal might be better for this thinking about it. Jitter is expressed in time units and has a peak and average value. Looking at the deviation can give you an idea what the mechanism is. That is a job for Matlab and a DSO.
Hi fastcat95,
NEC has always made high quality goods. The question is more wear as this is an old CDROM transport.
-Chris
You can measure jitter off the CD by looking at the eye pattern. The amount of horizontal shift is caused by jitter if you are triggering properly, otherwise noise can cause the same effect. The EFM signal might be better for this thinking about it. Jitter is expressed in time units and has a peak and average value. Looking at the deviation can give you an idea what the mechanism is. That is a job for Matlab and a DSO.
Hi fastcat95,
NEC has always made high quality goods. The question is more wear as this is an old CDROM transport.
-Chris
anatech said:
Hello Chris
I presume that jitter influence the eye patern because the laser take it's clock from the same quartz than all the cd player circuit, so that is why the jitter in the cd player circuit can be seen also in the eye patern ?
Btw, I just found an image about jitter influence on the eye patern.
Thank for your help
Bye
Gaetan
An externally hosted image should be here but it was not working when we last tested it.
Hi Gaetan,
Your eye pattern diagram looks like a telecom (T1, T3 or optical) type. I have attached a CD eye pattern. The characteristics you are looking for are the same.
The spindle motor is controlled by the difference between the PLL and the system clock. So, you are right in that the clock in the CD is the reference. Understand that the clock in the CD is more than accurate enough for this purpose. The speed induced jitter from the CD data is magnitudes higher than the CD clock. So replacing the clock in the CD will have zero effect on the jitter from the CD data stream. It's effects are felt elsewhere in the system.
-Chris
Your eye pattern diagram looks like a telecom (T1, T3 or optical) type. I have attached a CD eye pattern. The characteristics you are looking for are the same.
The spindle motor is controlled by the difference between the PLL and the system clock. So, you are right in that the clock in the CD is the reference. Understand that the clock in the CD is more than accurate enough for this purpose. The speed induced jitter from the CD data is magnitudes higher than the CD clock. So replacing the clock in the CD will have zero effect on the jitter from the CD data stream. It's effects are felt elsewhere in the system.
-Chris
Attachments
anatech said:
Hello
There is a lot of web page about jitter reduction for cd players... they suggest a lot of things; better power supply, reclocking (syncronous or asyncronous), shielding the dac chip, coax cable everywhere, putty over the crystal, etc...
But which web pages you would know to be more reliable ?
Thank
Bye
Gaetan
Hi Gaetan,
I don't think you can blindly go through and "improve things". First you need to ensure the CD player is properly adjusted and that the mechanical parts are okay. This means clamper, disc motor, all sliding surfaces and that the laser pickup is operating properly. Once you have done all this, the sound quality may have improved - for real. That's because you may have solved real problems.
Power supply. If it's an older unit, some capacitors may be tired or outright bad. The rectifiers are fine, but snubbing components will reduce hash. Solder joints on hot components may need to be redone.
Reclocking (syncronous or asyncronous). That is a tiny improvement, if it makes a difference at all. Approach with extreme caution.
Shielding the dac chip. Probably not and it may cause early failure. You may notice that some DAC chips run hot. Do not block the air flow! Gluing on a heat sink designed for IC's using thermal epoxy might help. It can't hurt if you them want to ground this. In this case then, doing it this way, you may extend the life of the chip and possibly reduce some low level noise due to the reduced temperature. What works and what doesn't depends on many things. Grounding the heat sink will not hurt anything, so try it.
Coax cable everywhere. That may cause signal attenuation. I wouldn't do this. Wire routing while listening to a silence track may bring some improvement. We call that "lead dress" and it can be moved to the wrong spot by poking fingers.
Putty over the crystal. No putty, please! A small amount of silicon adhesive may help. Make sure it stays pliable. You are attempting to damp vibrations here - so think about the goal and use as little stuff as you can to do the job. More is not better.
Please, a good technician is the one who should be doing this work. Someone who understands how a CD player works and what is a reasonable goal for improvements. There are a number of other things that will probably improve the sound quality. It depends greatly on the state of things and design as to the level of (and if) improvement.
-Chris
I don't think you can blindly go through and "improve things". First you need to ensure the CD player is properly adjusted and that the mechanical parts are okay. This means clamper, disc motor, all sliding surfaces and that the laser pickup is operating properly. Once you have done all this, the sound quality may have improved - for real. That's because you may have solved real problems.
Power supply. If it's an older unit, some capacitors may be tired or outright bad. The rectifiers are fine, but snubbing components will reduce hash. Solder joints on hot components may need to be redone.
Reclocking (syncronous or asyncronous). That is a tiny improvement, if it makes a difference at all. Approach with extreme caution.
Shielding the dac chip. Probably not and it may cause early failure. You may notice that some DAC chips run hot. Do not block the air flow! Gluing on a heat sink designed for IC's using thermal epoxy might help. It can't hurt if you them want to ground this. In this case then, doing it this way, you may extend the life of the chip and possibly reduce some low level noise due to the reduced temperature. What works and what doesn't depends on many things. Grounding the heat sink will not hurt anything, so try it.
Coax cable everywhere. That may cause signal attenuation. I wouldn't do this. Wire routing while listening to a silence track may bring some improvement. We call that "lead dress" and it can be moved to the wrong spot by poking fingers.
Putty over the crystal. No putty, please! A small amount of silicon adhesive may help. Make sure it stays pliable. You are attempting to damp vibrations here - so think about the goal and use as little stuff as you can to do the job. More is not better.
None. Ever notice that everything done results in a veil being lifted from in front of the music. Is this the dance of a thousand veils?? I you expect to hear a difference - you will.
Please, a good technician is the one who should be doing this work. Someone who understands how a CD player works and what is a reasonable goal for improvements. There are a number of other things that will probably improve the sound quality. It depends greatly on the state of things and design as to the level of (and if) improvement.
-Chris
Hi Gaetan,
Reclocking can make a difference if the system is good enough and there was a problem with jitter.
Think very carefully where the weak spots are in your own player. The advice I gave you is meant to address those first. Then try to find the biggest problem and try to fix it.
Do not judge your own work. The best thing to do is get the work done in small steps. Your wife or children will tell you if they hear a difference. It may take a couple days and it will not always be positive.
"Honey, what did you do to the <victim device>?" This means you have found something that changes the performance. It's a good thing. If they do not comment, you simply did whatever to make yourself feel better.
-Chris
So are Ford cars. This has nothing to do with quality, it's a fad. Big $$ for a simple job.
Reclocking can make a difference if the system is good enough and there was a problem with jitter.
Think very carefully where the weak spots are in your own player. The advice I gave you is meant to address those first. Then try to find the biggest problem and try to fix it.
Do not judge your own work. The best thing to do is get the work done in small steps. Your wife or children will tell you if they hear a difference. It may take a couple days and it will not always be positive.
"Honey, what did you do to the <victim device>?" This means you have found something that changes the performance. It's a good thing. If they do not comment, you simply did whatever to make yourself feel better.
-Chris