anatech said:Hi Andy,
Okay, I dare you!
-Chris
Already done !!!!!
http://www.diyaudio.com/forums/showthread.php?s=&threadid=110023
Andy
anatech said:Hi Andy,
Okay, I dare you!
Hi Kurt,
That isn't necessary. The normal triggering works great. Doing anything else would only make the measurements more of a pain. If you need to go that far, the eye pattern is not stable enough anyway (so all is lost).
Normal triggering has always worked well for me on every single CD player I've run across so far. Now, thinking about it a bit... A trigger from an internal clock may give a "messier" looking pattern (high jitter). The clock is not directly locked to the data rate of the CD. To get around this problem, the data is clocked into ram using a PLL and clocked out using the system clock. The difference between the PLL and system clock generates the disc motor correction signal for speed. So if you use anything but the actual eye pattern you will not be synced properly. Therefore there will be lots of time scale errors.
Hi maxlorenz,
Who? Me?
-Chris
Hi
If you can find the signal: Triggering on the disc rotation pulse gives a lot of useful info......
best
Guido
No, just unwanted effects like temperature drift.
Rubidium was used precisely because it was stable at one frequency. It's nothing like a crystal that can sometimes be "pulled" a little in frequency. HP still gets a lot for these as frequency standards.
BTW, this kind of accuracy for CD playback use is a complete waste. Overkill past worth considering. You might be able to use WWV at 5, 10 or 15 MHz as a comparative standard if you want. That would be good to lock a crystal oscillator to (5,10 or 15 MHz).
-Chris
Hello everyone,
I agree with anatech that a clock won't fix the signal if there is errors from the reading itself. But I found this :
http://benjamin.silvestre.club.fr/cd723/compteur/compteur.html
This french diyer counts the errors flags on a simple Philips cd723 and guess what... there is no sample error flag on a real CD even with this low price mechanic... So if you put a good clock to synchronize the data release by the FIFO buffer I guess you can say the signal is perfect! Even if you get 1 or 2 errors (which is not the case with a good surface CD), does it make a world of difference considering you get 44100 datas per second? Especially considering that the missing value is interpolated and not left blank.
The only problem is with the old CDR and only on the last track but it's not a real problem since we all respect copyright property here (don't we?).
Any comment?
I agree with anatech that a clock won't fix the signal if there is errors from the reading itself. But I found this :
http://benjamin.silvestre.club.fr/cd723/compteur/compteur.html
This french diyer counts the errors flags on a simple Philips cd723 and guess what... there is no sample error flag on a real CD even with this low price mechanic... So if you put a good clock to synchronize the data release by the FIFO buffer I guess you can say the signal is perfect! Even if you get 1 or 2 errors (which is not the case with a good surface CD), does it make a world of difference considering you get 44100 datas per second? Especially considering that the missing value is interpolated and not left blank.
The only problem is with the old CDR and only on the last track but it's not a real problem since we all respect copyright property here (don't we?).
Any comment?
Hi Hyldal,
Well, the Sony KSM213C seems to be a cheaper version than the KSM210 was. I haven't played with that one much.
The VAM1202 is extremely inconsistent in quality. Why waste your time with a product that has such high QC problems to begin with, and then a strong track record of no spares? Beats me.
Hi darian,
At the recent Burning amp show, a fellow DIYer was under the impression that he was able to make bit perfect copies. Sadly, I know this not to be true in most cases.
Case in point. When ripping a CD, it takes much more time if you want higher quality. Also, CD players used to allow us access to the error correction flags. The C1 flag means the data is bad and needs correction. Due to the way the data is repeated in many frames, this is possible to do. The C2 flag is the bad one. This one means that the sample could not be reconstructed - period. That means that this sample is beyond correction. Bad. Beyond hope. Finished. Unusable. I hope I've made my point here. The C2 flag normally does operate on a good CD some.
When the C2 flag does go up, the data is flagged as bad. At this point the DSP can do one of several things.
1) Pass the data to the DAC. Cheap units did / do this.
2) Mute the signal (send logical zero). This is a little better.
3) Repeat the last value. This is better still.
4) Interpolate the value. This is the best solution and is a guess.
Audibility is another kettle of fish. You probably will not hear one bad sample. A bunch of bad samples may create digital noises.
Just accept that CD playback is not perfect. Also accept that software and hardware will do everything possible to hide that truth from you. So, why aren't the C1 and C2 flags normally accessible any more? It's not because these cheap transports are better than the well built ones of yesterday. That is something you can be sure of.
-Chris
Well, the Sony KSM213C seems to be a cheaper version than the KSM210 was. I haven't played with that one much.
The VAM1202 is extremely inconsistent in quality. Why waste your time with a product that has such high QC problems to begin with, and then a strong track record of no spares? Beats me.
Hi darian,
At the recent Burning amp show, a fellow DIYer was under the impression that he was able to make bit perfect copies. Sadly, I know this not to be true in most cases.
Case in point. When ripping a CD, it takes much more time if you want higher quality. Also, CD players used to allow us access to the error correction flags. The C1 flag means the data is bad and needs correction. Due to the way the data is repeated in many frames, this is possible to do. The C2 flag is the bad one. This one means that the sample could not be reconstructed - period. That means that this sample is beyond correction. Bad. Beyond hope. Finished. Unusable. I hope I've made my point here. The C2 flag normally does operate on a good CD some.
When the C2 flag does go up, the data is flagged as bad. At this point the DSP can do one of several things.
1) Pass the data to the DAC. Cheap units did / do this.
2) Mute the signal (send logical zero). This is a little better.
3) Repeat the last value. This is better still.
4) Interpolate the value. This is the best solution and is a guess.
Audibility is another kettle of fish. You probably will not hear one bad sample. A bunch of bad samples may create digital noises.
Just accept that CD playback is not perfect. Also accept that software and hardware will do everything possible to hide that truth from you. So, why aren't the C1 and C2 flags normally accessible any more? It's not because these cheap transports are better than the well built ones of yesterday. That is something you can be sure of.
-Chris
Hello everyone,
To Anatech,
I remember about some article where they said the CD copy was almost bit perfect when done at SLOW SPEED (X1 or X2). We can imagine easily there is less reading errors at slow speed. The remaining error is the new jitter introduced by the burning process.
what do you think about it?
To Anatech,
I remember about some article where they said the CD copy was almost bit perfect when done at SLOW SPEED (X1 or X2). We can imagine easily there is less reading errors at slow speed. The remaining error is the new jitter introduced by the burning process.
what do you think about it?
Hello,
Anatech & Darian, you say that burning a C.D. at high speed is inferior to slow speed, because there is more scope for errors etc.I agree it makes sense but I recently tried burning C.D.,s at different speeds and looking at the recovered R.F. (eye pattern).There was a very noticable worsening of the envelope at the slower speeds, particularly the lower half where it was very noisy & "crushed".The highest speed my drive supports is X20 and the "visual" quality at this speed is pretty much as an original C.D. All speeds play back perfectly however.
Anatech, you seem to have a lot of practical experience on pickups and I wonder if you have ever come across this, I said above that the slower burned discs play perfectly and they do.However you cannot always stop them.Pressing stop and the disc may continue to spin for perhaps 20secs before letting you eject it.Other times on pressing stop the servo will lose lock and the disc will "take off". This NEVER happens on original discs or Hi-Speed burns. Optical block is CDM12.4/05 in Micromega Stage 2.
Thanks
Anatech & Darian, you say that burning a C.D. at high speed is inferior to slow speed, because there is more scope for errors etc.I agree it makes sense but I recently tried burning C.D.,s at different speeds and looking at the recovered R.F. (eye pattern).There was a very noticable worsening of the envelope at the slower speeds, particularly the lower half where it was very noisy & "crushed".The highest speed my drive supports is X20 and the "visual" quality at this speed is pretty much as an original C.D. All speeds play back perfectly however.
Anatech, you seem to have a lot of practical experience on pickups and I wonder if you have ever come across this, I said above that the slower burned discs play perfectly and they do.However you cannot always stop them.Pressing stop and the disc may continue to spin for perhaps 20secs before letting you eject it.Other times on pressing stop the servo will lose lock and the disc will "take off". This NEVER happens on original discs or Hi-Speed burns. Optical block is CDM12.4/05 in Micromega Stage 2.
Thanks
Hello again,
To AndrwT,
There is a new jitter induced by the burning process because the "cups" are burned according to the jitter of the computer (or other device) clock combined to the mechanic jitter of the CD burner. It's replaced by the jitter of the player after the FIFO but it is worth mentionning.
To AndrwT,
There is a new jitter induced by the burning process because the "cups" are burned according to the jitter of the computer (or other device) clock combined to the mechanic jitter of the CD burner. It's replaced by the jitter of the player after the FIFO but it is worth mentionning.
Hi Andrew,
Any digital system can suffer from jitter. This is well known in the T&M field. Another name for this is "timing errors". Jitter is very important in high speed communication lines, hard drives and just about everything else where data is present.
Hi Mooly,
All "burnable" CDs or DVDs have the tracks preformed. You are still at the mercy of the recording system servo errors. Speed, focus and tracking are all imperfect. The other factor is that the reflectivity is not the same as a manufactured disc. This shifts the slice level and may result in an RF signal that is too low or too high. Either one has serious issues. The play back machine servos deal with these things the best they can. We did go through a time where recorded CDs would run the laser to the complete rear of the track and rip the gears up.
To answer some of your last queries, different systems deal with defects in different ways. So you are seeing a combination of effects that result in what the CD player seems to be doing. I can't say unless it is sitting on my bench so I can examine the servo signals and RF pattern.
A different brand of recordable blanks may solve your issue. It sounds like the servos in the player are not happy with something. I'll bet the recording speed is not the issue in this case.
Hi Darian,
-Chris
Any digital system can suffer from jitter. This is well known in the T&M field. Another name for this is "timing errors". Jitter is very important in high speed communication lines, hard drives and just about everything else where data is present.
Hi Mooly,
All "burnable" CDs or DVDs have the tracks preformed. You are still at the mercy of the recording system servo errors. Speed, focus and tracking are all imperfect. The other factor is that the reflectivity is not the same as a manufactured disc. This shifts the slice level and may result in an RF signal that is too low or too high. Either one has serious issues. The play back machine servos deal with these things the best they can. We did go through a time where recorded CDs would run the laser to the complete rear of the track and rip the gears up.
To answer some of your last queries, different systems deal with defects in different ways. So you are seeing a combination of effects that result in what the CD player seems to be doing. I can't say unless it is sitting on my bench so I can examine the servo signals and RF pattern.
A different brand of recordable blanks may solve your issue. It sounds like the servos in the player are not happy with something. I'll bet the recording speed is not the issue in this case.
Hi Darian,
Sorry, this is not true. The error flag may be suppressed in that machine. We had really good transports earlier in time. The bit error rates were lower than the newer drives and things have only got worse over time. He can say what he wants, but the truth of the matter is that there are C2 errors when playing a CD normally. It's a fact of life. If you look at the data stream, there will probably be no error signals because "corrective action" has taken place. This means we are feeding the DACs a signal that has no CRC errors. That does not mean that the CD data was read without errors, it just means that the data we send to the dacs have no illegal values. That is a large difference from error free.
-Chris
Hello Anatech
On the cd723 measuremement the french DIYer had :
1 to 15 per second C1/C2 flags on a new CD,
30-150 on an old CD,
up to 2000 on an old CDR.
But the real point is that it resulted in :
0 sample error on the new and old CDs,
0 to 2 sample errors for the old CDR until the last track where he had more than 100 sample errors per second (gasp)
So you can see that the reading process may be flawed, the sample errors are rare, at least on a real CD. So I think this mechanic is not that bad. Perhaps an upscale one would have made errors on the old CDR too...
On the cd723 measuremement the french DIYer had :
1 to 15 per second C1/C2 flags on a new CD,
30-150 on an old CD,
up to 2000 on an old CDR.
But the real point is that it resulted in :
0 sample error on the new and old CDs,
0 to 2 sample errors for the old CDR until the last track where he had more than 100 sample errors per second (gasp)
So you can see that the reading process may be flawed, the sample errors are rare, at least on a real CD. So I think this mechanic is not that bad. Perhaps an upscale one would have made errors on the old CDR too...
Hi Darian,
These days I don't know if you would have access to the C1 and C2 flags. Monitoring the serial data would only show valid data as corrective measures have been executed. Note that this correction only presents in range values to the DAC in the event of a C2 error. This has exactly zero to do with the original data value. The only similarity is that an attempt has been made to guess at it's value from surrounding good data.
Now, for a really fun time, feed the EFM signal into an old chip set as well and watch the flags. It ain't gonna be perfect. The only change between a current chip set and an old one will be what happens to the C2 data. The presence of the C1 and C2 errors is largely unaffected. That is straight math and hopefully some good ram.
-Chris
Actually, those readings are very normal. Please pay attention to the C2 error rate. This is the uncorrectable error flag. The C1 error flag will be much higher, also normal. C2 errors occur when there are read errors on one frame, and also on previous and successive data frames so that the distributed data is also unavailable. This makes that frame and possibly data frames around it bad to the extent that they are also flagged at the C2 level. A number of these bad samples in series can be expected to result in audible noise. A single bad sample (but in range data) presented to the DAC would probably go completely unnoticed.
These days I don't know if you would have access to the C1 and C2 flags. Monitoring the serial data would only show valid data as corrective measures have been executed. Note that this correction only presents in range values to the DAC in the event of a C2 error. This has exactly zero to do with the original data value. The only similarity is that an attempt has been made to guess at it's value from surrounding good data.
Now, for a really fun time, feed the EFM signal into an old chip set as well and watch the flags. It ain't gonna be perfect. The only change between a current chip set and an old one will be what happens to the C2 data. The presence of the C1 and C2 errors is largely unaffected. That is straight math and hopefully some good ram.
-Chris
Hi Anatach,
Thanks for taking the time to reply. I have tried different media from Sony, Philips & T.D.K. and all seem pretty similar with regard to the poorer envelope/slow burn characteristic.An issue perhaps with my burner ? I think you have something with the slice level as I seem to remember the 3T-11T signals were not in the centre of the recovered waveform and that their relative amplitudes were not as per a standard C.D. Many thanks once again for your comments.
Karl
Thanks for taking the time to reply. I have tried different media from Sony, Philips & T.D.K. and all seem pretty similar with regard to the poorer envelope/slow burn characteristic.An issue perhaps with my burner ? I think you have something with the slice level as I seem to remember the 3T-11T signals were not in the centre of the recovered waveform and that their relative amplitudes were not as per a standard C.D. Many thanks once again for your comments.
Karl
Slightly off topic, and for some thread candy...
Here are two pics of a mechanism from a sony dvd player I dumpsterized. I think this was the pin based lens mechanism mentioned earlier in the thread. It seems very cleverly designed and I like the magnetic levetation of the lens. Do any of you happen to know the type of drive this is?
Jitter me timbers arrgh!
Here are two pics of a mechanism from a sony dvd player I dumpsterized. I think this was the pin based lens mechanism mentioned earlier in the thread. It seems very cleverly designed and I like the magnetic levetation of the lens. Do any of you happen to know the type of drive this is?
Jitter me timbers arrgh!