pre-emphasis and archiving and cdda2wav

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Kjoerup
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Postby Kjoerup » Sun Oct 03, 2004 10:32 pm

Not to get too far off topic, but I have wondered about something relating to (I guess it is) the PQ subcode. I have 4 "copy controlled" Kevin Ayers CDs, which use CDS 300. I was able to extract all of the audio info intact (no clicks!) using Missing Media Media Burner, but the time info was incorrect. When I'd place the individual files into Bias Peak, the program would return an error, saying it couldn't locate the end of the file. It was a minor error, as the sound file would still come up and would play fine. Further poking around with this led me to discover that the time of the track was off by just a few frames. That is, I discovered, one of the tricks used by Cactus Data Shield for "copy protection".

Now, copying and saving the ripped file as another aiff or wave or whatever always resulted in an incorrect time duration. Trying to convert to lossy mp3 in LAME yielded the same incorrect result. But when I converted the aiff file to FLAC and/or Apple Lossless the problem was gone! The time was now correctly reported. Converting those lossless files back to aiff also preserved the correct times. Problem solved at last! Strange, isn't it?

My theory, then, is this: even though the PQ subcode info is not carried over when exporting an individual track, it appears that the ripper initially obtains the time info from the PQ subcode and treats it as gospel, whether it is actually correct or not. I can only conclude that protection schemes like Cactus Data Shield are taking advantage of this flaw in CD rippers. (Certainly Toast and cdda2wav have this flaw. Perhaps EAC is more "intelligent" in this regard? I've never used it, so I don't know. I've asked at Hydrogen Audio, searched all over the net, and have never found an answer to any of this. BTW, what I'm describing isn't simply a by-product of one CD-ROM drive either; I've ripped these discs in an external Plextor, an external Yamaha, and an internal DVD-ROM drive -- same thing happens. Obviously, CDS "protection" fools with the time subcode in order to confuse ROM drives.)

What I can't really answer is why converting, say, an aiff to a wave file still preserves the incorrect time info, but going from aiff to FLAC or Apple Lossless results in a correct time. My guess is that these lossless codecs -- or at least the programs running them -- are designed to be more "intelligent", ignoring the given time duration, and will instead count the actual frames in the sound file.

Something to keep in mind if you ever encounter a problem like this. You may be able to play sound files with incorrect times on a computer without noticing any ill effects, but these incorrect times will cause havoc if you attempt to burn them to CD or convert the files to another format.

It took me five nights of increasingly mounting frustration and bewilderment to figure all of this out! So I thought I'd pass on my hard won discoveries to whoever may find it of any use.

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krabapple
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Postby krabapple » Mon Oct 04, 2004 11:32 am

Kjoerup ,

The virtual CD is a great idea. I haven't encountered any pre-emphasized discs during this weekend's ripping, but maybe I'll pull out one of the CDs already done and redo as an experiment. If I do I'll report back here. I expect that indeed the hard part will be getting cdda2wav to recognize the 'CD' -- or actually, telling it where the 'CD' is! I'm not sure how to specify the desktop, versus the CDR drive, as a source.

The CDR method is one I've already used, actually; it works fine.

So far, only two or three, out of 900 or so discs in my collection, have been pre-emphasized. They were all classical music discs of of European early 80's vintage. (Though to be honest I didn't even think to check the pre-e status of most of my rock/jazz discs until recently. I may have to look at a few of the oldest ones again).
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krabapple
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Postby krabapple » Thu Mar 30, 2006 2:19 pm

remember pre-emphasis?

Guess which popular ripping software applies de-emphasis to pre-emphasized CDs when ripping tracks to wav?

itunes!

http://www.hydrogenaudio.org/forums/ind ... 38312&st=0

now, I don't know that this would work on a CD where the PE flag *isn't* recognized by something like EAC. Perhaps someone can try doing it with the Japanese Abbey Road and see.
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J_Partyka
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Postby J_Partyka » Fri Mar 31, 2006 6:43 am

krabapple wrote:now, I don't know that this would work on a CD where the PE flag *isn't* recognized by something like EAC. Perhaps someone can try doing it with the Japanese Abbey Road and see.


Yes, it works very well with the Japanese Abbey Road.

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lukpac
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Postby lukpac » Fri Mar 31, 2006 8:30 am

Do you have an original Jeff, or a CD-R?
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J_Partyka
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Postby J_Partyka » Fri Mar 31, 2006 9:02 am

lukpac wrote:Do you have an original Jeff, or a CD-R?


It's an original.

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lukpac
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Postby lukpac » Fri Mar 31, 2006 9:04 am

Ahh, cool. For some reason the PE on my CD-R shows up fine in EAC, IIRC.

At some point it might be nice to have an original, but it's just not worth $100 to me...
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Patrick M
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Postby Patrick M » Fri Mar 31, 2006 9:05 am

If anyone wanted to burn me a copy, that would be nice. (hint, hint)
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J_Partyka
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Postby J_Partyka » Fri Mar 31, 2006 9:06 am

lukpac wrote:At some point it might be nice to have an original, but it's just not worth $100 to me...


I actually stumbled upon mine in a store recently. It was priced well below $100 because the booklet had suffered some damage. The disc was fine, though, and it looked genuine ... so I went for it.

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lukpac
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Postby lukpac » Fri Mar 31, 2006 9:22 am

Patrick M wrote:If anyone wanted to burn me a copy, that would be nice. (hint, hint)


Nahh.

Honestly, I still fail to see what the big deal is. There are some small differences here and there, and if I was really paying attention *maybe* I could detect them in an A/B/X, but for the most part it really isn't much different from the stock CD.

All IMHO, of course.
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krabapple
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Postby krabapple » Fri Mar 31, 2006 11:43 am

J_Partyka wrote:
krabapple wrote:now, I don't know that this would work on a CD where the PE flag *isn't* recognized by something like EAC. Perhaps someone can try doing it with the Japanese Abbey Road and see.


Yes, it works very well with the Japanese Abbey Road.


OK,if not I was going to suggest that someone can rip and disc manually set the PE flag, then burn it to CDR , then re-rip and run it through itunes.\(I was under the impression the the Beatles CD 'fooled' EAC by not displaying PE, but I haven't been following that closely.) I think I had something like three discs out of ~850 that showed PE in EAC, when I did my collection archiving. Is there a list anywhere of discs that *don't* show their PE status correctly in EAC?
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Postby Ess Ay Cee Dee » Fri Mar 31, 2006 4:37 pm

I downloaded a FLAC'ed version of the Toshiba Abbey Road at Oink a few months ago. The uploader graciously included a CUE sheet with PE flags and it sounds fine to my ears; the high end sounds natural, so I assume that my burned copy is identical to an original.

If any of you are desperate for a copy, send me a PM.

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MK
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Postby MK » Sat Apr 08, 2006 11:08 am

I have an original, but when I tried importing the files as .wav files through iTunes, it didn't de-emphasize them. It's the most recent iTunes and on Windows XP...do I need a Mac? (and if I do, do I need to import them as .wav files, or can I import them as aif files?)
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J_Partyka
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Postby J_Partyka » Sat Apr 08, 2006 12:21 pm

MK wrote:I have an original, but when I tried importing the files as .wav files through iTunes, it didn't de-emphasize them. It's the most recent iTunes and on Windows XP...do I need a Mac? (and if I do, do I need to import them as .wav files, or can I import them as aif files?)


Hmm, that's odd. I extracted Abbey Road successfully on a Mac, but I also have a Dell laptop running XP and I extracted the pre-emphasized Columbia The Wall CD successfully on that.

In both cases, I extracted to WAV files. Perhaps I can do a little testing (with Abbey Road on the PC, and with AIF files in general) to help answer your questions.

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Postby Crummy Old Label Avatar » Sat Apr 08, 2006 6:28 pm

So is this due to QuickTime, iTunes itself (doubtful; why would iTunes have extra code just for this when it uses QT as its engine), or Core Audio?

I wonder if iTunes/QuickTime always did this? If this is something new, I'm wondering if it has to do with Core Audio? Core Audio is relatively new, native to OS 10.4. If you are on 10.4 and have Max installed, look at your Core Audio export options; you'll see that Core Audio is an extraordinarily flexible and advanced engine.

I'd test this (Mac user), but I don't own a CD with pre-emphasis (not one that I'm aware of, anyway).
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