Peter Daniel said:
They're actually not used while reading the disc. They're only used after the output of the photodiodes has been converted from an analog RF signal to pulses, decoded and finally demodulated.
The reason error correction is used is to correct errors I would imagine.
Can't say I recall any companies claiming superior error correction algorithms. Perhaps they're claiming to be able to correct for larger bursts of errors than their competition. There's really only one error detection/correction system and that's the one that's part of the CD spec. The Cross-Interleave Reed-Solomon code (CIRC).
So without knowing the specific claims made by manufacturers regarding error detection/correction, there's not much else I can say.
se
Peter,
CDs can have different flaws:
metallisation can have pinholes
polycarbonate can have inclusions and striae, both changing the refraction index locally and also bringing birefringence into the game.
There can be all sort of surface imprefections, acting as µprisms.
Such flaws are almost undetectable with the bare eye. Particularly those influencing refraction index depent on the polarizon plane of the incoming polarized laser light.
Have a talk with Mr Thevissen, he will tell you how big the device-generated and CD-generated flaw rate is; the CD-PRO2 drive is sold to CD manufacturers to measure CD-generated error rates.
CDs can have different flaws:
metallisation can have pinholes
polycarbonate can have inclusions and striae, both changing the refraction index locally and also bringing birefringence into the game.
There can be all sort of surface imprefections, acting as µprisms.
Such flaws are almost undetectable with the bare eye. Particularly those influencing refraction index depent on the polarizon plane of the incoming polarized laser light.
Have a talk with Mr Thevissen, he will tell you how big the device-generated and CD-generated flaw rate is; the CD-PRO2 drive is sold to CD manufacturers to measure CD-generated error rates.
Steve Eddy said:
I think there is more to CD playback errors than just that. My reasoning was that maybe LED somehow helps to reduce the errors occuring while reading encoded data on a CD.
A friend of mine got in touch with mad scientist who is purchasing big lots of CDs and measure them for quality. Not too many from the same batch is really good, but the ones he chooses sound noticably better than the others.
Peter Daniel said:
Than just what? My list wasn't all-inclusive. Hence the "etc." at the end.
Up to this point, I can't think of any reason why it would either reduce or even increase them.
Well you can measure your own discs in terms of errors. Just monitor the C1 and C2 error flag pins on the decoder chip in your CDP.
se
a) talk to Mr Thevissen is a good idea. He will tell You the block error rete of CD PRO is about ten times better than usual CD transports.
b) as long as you don´t measure you can´t say with LED there are less errors. You only recongince a different and maybe better sound. Ok, maybe thsi is some placebos, psycho etc effect. Maybe your CD PRO resd more errors with LED, and error correction has to smooth them / shape them away. So the sound is less exact, more error, farer from original information. But maybe you feel it sound better this way.
c) Try: make a wav file on your computer stereo channel 1 signal, channel 2 signal * (-1) , 180° phase lag. burn its on CD. play CD on CD PRO . tie both outputs toghether via resistors against ground or so. measure what comes out - with and -without LED. Any difference?
Try different signals as .wav file, like pink noise etc.
Bit error rates
Has any of you made any experiments checking the error rate
while playing CDs? I remember a local HiFi-shop doing this a
long time ago, connecting a frequency counter to the signal
indicating non-correctable errors. I don't remember any figures,
but it was a surprisingly high frequency. This was about 15 years
ago, so it has most likely improved for the higher-end segment
of players. However, mechanical build is generally not as rigid
as it used to be, and even some quite expensive players are
very crappy in this respect. In my limited experience there is
a clear correlation between mechanical buld and sonics. Not that
a player can get along with a crappy DAC, but I don't think any
company today would take the cost of rigid mechanics unless
they already have a quite good DAC. On the other hand, a good
DAC cannot save you from bit errors due to bad mechanical build.
I think most read errors are not repeatable errors due to
imperfections in the CD itself, although such imperfections may
increase the likelihood of read error. Some people report that
CDR copies of CDs sound better than the originals. I thnk this
is technically reasonable. CDRs are usually much thicker and
sturdier than pressed CDs and they usually have a better
reflective layer. I didn'tnotice any clear difference last time I
tested this, but I bought a better CD player recently, so maybe
I should try it again? Also, the brand and type of CDR makes
difference here (if there is any difference at all, that is
).
Opinions? Experiences?
Has any of you made any experiments checking the error rate
while playing CDs? I remember a local HiFi-shop doing this a
long time ago, connecting a frequency counter to the signal
indicating non-correctable errors. I don't remember any figures,
but it was a surprisingly high frequency. This was about 15 years
ago, so it has most likely improved for the higher-end segment
of players. However, mechanical build is generally not as rigid
as it used to be, and even some quite expensive players are
very crappy in this respect. In my limited experience there is
a clear correlation between mechanical buld and sonics. Not that
a player can get along with a crappy DAC, but I don't think any
company today would take the cost of rigid mechanics unless
they already have a quite good DAC. On the other hand, a good
DAC cannot save you from bit errors due to bad mechanical build.
I think most read errors are not repeatable errors due to
imperfections in the CD itself, although such imperfections may
increase the likelihood of read error. Some people report that
CDR copies of CDs sound better than the originals. I thnk this
is technically reasonable. CDRs are usually much thicker and
sturdier than pressed CDs and they usually have a better
reflective layer. I didn'tnotice any clear difference last time I
tested this, but I bought a better CD player recently, so maybe
I should try it again? Also, the brand and type of CDR makes
difference here (if there is any difference at all, that is
).Opinions? Experiences?
Re: Bit error rates
Interesting.
Back in the mid-late 80s, a group of us on CompuServe's CEFORUM (back in its heyday) were wanting to get some answers in that regard as well.
I built a simple four digit counter and it was sent along to a number of participants there.
We found it was rather rare that a disc had ANY uncorrectable errors. Most discs had no uncorrectable errors and of those that did, there were only a handful of them.
I wonder if that dealer you mention was monitoring the wrong pin? If they monitered the C1 fail pin, then yes, they'd see quite a few errors. But if you want to determine the number of uncorrectable errors, you need to monitor the C2 fail pin. It's only errros which fail C2 that get interpolated (or if there are too many, the machine just mutes itself).
se
Christer said:
Interesting.
Back in the mid-late 80s, a group of us on CompuServe's CEFORUM (back in its heyday) were wanting to get some answers in that regard as well.
I built a simple four digit counter and it was sent along to a number of participants there.
We found it was rather rare that a disc had ANY uncorrectable errors. Most discs had no uncorrectable errors and of those that did, there were only a handful of them.
I wonder if that dealer you mention was monitoring the wrong pin? If they monitered the C1 fail pin, then yes, they'd see quite a few errors. But if you want to determine the number of uncorrectable errors, you need to monitor the C2 fail pin. It's only errros which fail C2 that get interpolated (or if there are too many, the machine just mutes itself).
se
Steve,
It might be as you suggest, that they monitored the wrong pin.
I just know what they told me. If I remember correctly, it was
a Marantz player, which they considered very good by then,
ie. in the mid-late 80s somewhere.
BTW, I know that the odd and even samples are separated into
different blocks, so it is possible to reproduce the signal with
half the actual sample frequency if only one block is misread.
Would this pass as a correctable error or not?
It might be as you suggest, that they monitored the wrong pin.
I just know what they told me. If I remember correctly, it was
a Marantz player, which they considered very good by then,
ie. in the mid-late 80s somewhere.
BTW, I know that the odd and even samples are separated into
different blocks, so it is possible to reproduce the signal with
half the actual sample frequency if only one block is misread.
Would this pass as a correctable error or not?
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