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Topic: Copy of cd sounds worse than original (Read 11925 times) previous topic - next topic
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Copy of cd sounds worse than original

Reply #25 –
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It's just data folks, if the source, burner and destination media are all free of defects and it's a digital-to-digital copy then you're hearing the placebo effect at work, just like with $50 a foot speaker wire.


I believe paulr.
We've heard hundreds of times people complaining that their CDRs can't be played in some audio players while they work in others.

Why not an intermediate state, where the CD can be played but the error concealment is so much that the sound is audibly different?

I haven't notice these problems with my players, but I don't think this is black and white: or your CDR plays perfectly or your player can't read it. There are people who suffers skips and clicks, and I guess there are also people whose players cannot read perfectly all the time but not enough to be clearly audible... maybe myself.

but maybe I'm wrong, I'm no expert...

Copy of cd sounds worse than original

Reply #26 –
"I've also observed that a 4X-speed SCSI-based CDR copy sounds inferior to a double-speed copy and yet again inferior to a 1X speed copy."

Sometimes when I play a copy of a game, the textures are different colors, slightly red-shifted due to the speed the cdr was burned at

Doesn't no matter what the info is being read from doesn't it eventually reach a buffer somewhere?  Wouldn't that get rid of any type of problem while reading?  He saying we can't have a good clock generator to keep a 44.1khz single?  That seems kinda bs, a cd drive having to work harder puts more of a load on the ps which affects the clock generator?  How bout in a computer, you have a cpu that can jump from 0w to 90w many times a second yet its clock generator never fails.  I may not get exactly what he's talking about but BLEH.  I'm going to go spend $500 on main cables for my computer, because alot of noise is added between teh wall and my computer..  and its affecting txt docuemnts, spelling errors keep popping up.

Copy of cd sounds worse than original

Reply #27 –
Quote
Sometimes when I play a copy of a game, the textures are different colors, slightly red-shifted due to the speed the cdr was burned at

Doesn't no matter what the info is being read from doesn't it eventually reach a buffer somewhere? Wouldn't that get rid of any type of problem while reading?

There's a difference here, cd-audio error recovery isn't as strong as cd-rom error recovery, and the cd player won't tell you if there are read errors, as opposed to a cd-rom reader.

Quote
He saying we can't have a good clock generator to keep a 44.1khz single?  That seems kinda bs, a cd drive having to work harder puts more of a load on the ps which affects the clock generator?  How bout in a computer, you have a cpu that can jump from 0w to 90w many times a second yet its clock generator never fails.


That's true, but you never know what's out there. I have an old portable Sony cd player that outputs *lots* of jitter, probably due to poor driving mechanism and/or power stability. It's very easy to see in a spectral view when playing a tone. (I haven't listened to it critically from years, even when I found the problem, so I don't know how it sounds).

Quote
I may not get exactly what he's talking about but BLEH.  I'm going to go spend $500 on main cables for my computer, because alot of noise is added between teh wall and my computer..  and its affecting txt docuemnts, spelling errors keep popping up.


I agree that some things are ridiculous, but others can't be rigorously discarded so easily, specially if there is some of what seems to be solid evidence, that seems to support it.

Copy of cd sounds worse than original

Reply #28 –
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If the two copies paulr did were bit-for-bit identical, and the results were truly 10 correct identifications out of 10 trials, and the only difference at the test was the cd played, and the listener really didn't have any clue of what was being played (equivalent to a double-blind test),

Technically it was a single blind test, not a double, since the tester knew which disks he was loading.
The reason that double blind is considered better is that with single blind the tester may either conciously
or subcounciously convey a bias to the subject either by the selection not being random, or inflection
of the voice.. "which do you like better,  A  or  B ?"

I would be interested in how he compared the disks..  Just compare the
length or a byte by byte compare?  MD5 checksum might be the easiest "good enough"method.


Quote
- The difference is not on the data read, but on timing problems (jitter) due to the higher work at the servo having an influence on the power supply of the clock and its stability, in case of the cdr playback. This is what paulr thinks that could happen.

I think the second explanation can be plausible, but would be sign of a poorly designed player.


Exactly... barring the constraints of a portable any decent player will at least have separate voltage
regulation for analog and digital circuits etc.  On the Marantz special editions in particular they always
started out with a pretty good player and one of the upgrades was in power supply and isolation.  So
I would expect that his player would be one of the LEAST susceptable to this effect. 

In my experience, even inside a chip a lot of effort goes into keeping a change in current draw in
one circuit from affecting the power supply voltage to another circuit.

Copy of cd sounds worse than original

Reply #29 –
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Doesn't no matter what the info is being read from doesn't it eventually reach a buffer somewhere?  Wouldn't that get rid of any type of problem while reading? 

The last link provided by dB refers to an old, but interesting paper : http://www.nanophon.com/audio/jitter92.pdf

We can see that proving that jitter is not audible is very difficult. In the worst case (120 db 20 kHz sine playback - 0 db sideband audible), a jitter of 20 ps may be audible !

The paper concludes "Several consumer DAC units have been examined - only one of which behaves in an appropriate manner when fed by a digital signal with jitter"
This was in 1992. I've read parts of it, but couldn't find all their DAC tests.

Copy of cd sounds worse than original

Reply #30 –
Too bad you don't have the CDs anymore. We'd have liked you to record the analog outpout of your CD player and make some MPC or MP3 files. I would have done the same with my Yamaha CDX860 player, that never showed any sensitivity to burned or pressed CDR, if you had sent me the CDs.

If you find another bad sounding copy and have the time to analogly and digitally copy short samples of it, we'd be very interested.

Copy of cd sounds worse than original

Reply #31 –
"In most cases, the final CDR sounds better than the source, as auditioned direct off the hard disk!"

Where is he playing the CDR?  On the computer?  Or does he mean burning it to cdr and playing in a nice cd player sounds better than though a computers jittery soundcard?



Anyways, looking at that picture on this link of an ideal bitstream vs jittery one....    theres 192khz soundcards and crap...  what if you resample to 176khz (whateve 4x44.1 is) no wave shaping or anything, wouldn't that push jitter away and not change the sound at all?

Copy of cd sounds worse than original

Reply #32 –
Quote
the only way you might have a copy where there is obvious degradation in sound quality is:

- defective DAE
- extreme jitter during the write process
- low quality burner that doesn't write data well
- cheap (very cheap ) CDR media
- if your friend did any kind of signal processing in, say, nero, just before he burned the CD

that sounds about right to me, but i'd add a couple of things.

- if we accept that extreme jitter during the write process can affect the sound, it seems reasonable that less extreme jitter will effect it in a less extreme way. that fits with my experience. some cd-r makes sounded very different to the original, others were only subtley different.

- isses that i've heard of effecting sound quality include wobbly CD spirals, variations in depth of the read surface and the characteristics of the dye.

- in my experience some cd players are very sensitive to these issues, many are not.

If you don't believe me get your info from Plextor.
www.plextor.be/english/pdf/PlextorVariRec.pdf

"VariRec can change the value of the laser power. The resulting effects are: change of sound quality of recorded disc (On many CD players there may a slight change, some kind of effect when VariREC is used on the different settings)..."

Copy of cd sounds worse than original

Reply #34 –
You should check the CRC numbers of the original CD vs. the burned copy using a program such as EAC. If the CRCs are the same, it would be safe to assume that the sound of the two CDs would be exactly the same, at least in that drive. Then, if you feel that you can hear a difference on a stand-alone CD deck between the two copies that your computer deems 100% identical, only two conclusions can be reached:

1.) The stand alone CD deck that you are using does not like burned CDs and introduces jitter and/or other errors into the sound that degrade sound quality.

2.) Placebo is at work.

The only way I would believe that a difference really could be heard is if the original & burned CDs had identical CRC numbers, but could be successfully ABXed in a double blind test using the stand alone CD deck. Until such a test is done, the original and the copy are exactly the same IMO.

Edit: I'm sick and not thinking straight..........

Copy of cd sounds worse than original

Reply #35 –
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You should check the CRC numbers of the original CD vs. the burned copy using a program such as EAC.

That's what he did (for a WAV compare is at least as good)

Copy of cd sounds worse than original

Reply #36 –
To check for read errors, there is no point in comparing CRCs. Different drive behave differently, and CRC OK in a computer doesn't mean CRC OK at all in the CD Player.

It is necessary, for ruling out data errors, to record the SPDIF output of the CD Player, with a soundcard capable of slaving its clock to the digital input and record bit by bit, and to compare the recordings of the two CDs between them.

The data comparison of PaulR just proves that the CD was properly copied (no lossy extraction/normalisation/etc)

Copy of cd sounds worse than original

Reply #37 –
I just remembered this morning that there is another simple possible explanation for the differences perceived it the test. I remembered this because paulr's test suggest that the differences were obvious, and this is quite strange. I remembered that this same thing happened to me with one particular old cd, a year ago or so, and in that occasion it made me wonder what could be going on.

I discovered that the analog output of my cd player when playing the original and when playing the copy were quite different, having the copy significant louder content at middle and high frequencies.

Then, I remembered that cd-audio specs allows for an optional pre-emphasis of the recorded signal, so that at playback the signal has to be de-emphasized to keep a flat response (something similar to RIAA eq) . This option is signaled by a special bit at the cd-audio data, bit that is lost when you extract the data in form of a wav. If the emphasis bit is lost, the extracted data will have an added emphasis that won't be corrected when played at the cd player. The pre-emphasis effect is not subtle, and this is what caused the obvious audible differences between the original cd (that was properly de-emphasized) and the copy (that was not de-emphasized due to the emphasis bit being lost).

This emphasis is described here : http://webclub.kcom.ne.jp/ma/takabin/eng/emphasis.html and more or less concides with what I measured.

This emphasis bit can be transmitted within a spdif stream, so even when the spdif audio data is identical, if it has the emphasis bit active it should be played in a different way than if it is not active. However, again, when recording a spdif stream into a standard audio file, the emphasis bit is lost.

I think pre-emphasized cds are not very common, and I don't know if this pre-emphasis is still used today's releases. But there is a possibility that the cd that paulr used at his tests were one of those.