A Copied CD sounds no different to the original

Posted by: DynaudioBoy on 15 May 2003

Hi

This is my first post. I am a Computer Science graduate and kinda want to say something about CD copies that may cause a reaction.

BTW I have recieved a NAC72/NAP140 and am enjoying it very much! and now awaiting on a hicap after some advice.

I am going to prove to everyone that a CD copy does sound exactly the same as the Original, and I have'nt even listened to both in a controlled blindfold test.

Sounds like magic, well it is it's the magic of digital.

First you will need to know how a CD works so click Here

Obivously there is only one way to store information on a CD whether it be audio or the computer software you are currently using to read this post, using pits. Now with these pits all you can store is numbers, it how you translate those numbers which determines what information is stored on the CD, like Audio or Software.

Click here to see how to store numbers using binary notation using those pits to represent a 1 (on) and the absent of a pit to represent 0 (off)

DVDs are exactly the same as CDs except have smaller pits which means more numbers and more of the information on it, whether it be audio/video/software hence better sound and picture. Software is a term to describe tools that are stored on CD like the internet browser you are using right now to read this post.

Now here is my point, everything that is stored on a CD is stored in exactly the same way using binary notation as shown by the howstuffworks website. Now when you read a CD using a computer if the CD is not damaged you will read exactly the same information everytime, there is a good reason for this. Computers "crash" go wrong don't do what thier told etc, this suprisingly is because a side effect of using binary. With binary there is no in between on and off, it either is working or it isn't. So if the CD is damaged and one of those bits are set wrong then the software will not work! So when you copy a piece of software (which is illegal due to copyrights), you are copying those 1s and 0s via reading the pits. If one of those pits are incorretly copied say a 1 was now a 0, that software will not function at all due to the side effect of digital.

Recap
When copying CDs you are copying 1s and 0s by reading pits.

Not copying audio/video or software.

It only becomes one of these forms when you interpret the numbers on the CD to actually be read in the required mode if you like, mode being audio/video/software.

So when you copy a software CD you get an exact copy of the original otherwise the software would'nt work.

When you copy a audio CD you get an exact copy of the original because the computer does'nt know what it is copying, it is just reading those pits and reproducing them on the CD copy (CDR).

So how can a copy of an audio CD sound any different at all to the original if it has exactly the same information on it?

Just like in the shops all the CDs in that shop as long as they don't have physical damage will sound exactly the same.

Posted on: 15 May 2003 by Mick P

Alan

I use Kodak disc's, I burn them in my pc at x1 speed and the copies are identical to the original.

Regards

Mick

Posted on: 15 May 2003 by Thomas K

Hi Dynboy,

I didn't even read your message properly because I'm sure I've read the theories many times before. In the eighties these explanations served to tell us how "digital" was the perfect medium -- funny how it keeps getting more and more perfect. (BTW, I only listen to CDs and I pity the poor souls who argue against digital because "the sound waves aren't smooth".)

I've not seriously tried to determine whether there are differences or not -- the few times I compared CD with CD-R, any perceived differences were too small to be unmistakenly real. But when I read up on some discussions in several google groups, I found record company employees (matter-of-factly types) discussing huge problems they had with the inconsistent quality of bit-identical pressings. Now somehow I can't imagine these people discussing figments of their imagination (I'm sure they would prefer not to have these problems, so they're hardly in it for the ideology).

IIRC Bob Katz reckons that you can make numerous bit-identical copies using cheap drives blah blah, all of which will sound inferior to the source ("Bob didn't study engineering, so ner."). However, he's found when you take one of those copies and bring the data back onto a high-quality digital medium (whatever that may be), your sound quality is restored again. Now whaddaya make of that? Is he one of those high-end loonies? Is he a die-hard digital-is-perfect fan? Is the world maybe not as simple as we would like it to be?

Thomas

Posted on: 15 May 2003 by Trevor Warwick

You're mistaken in your assertion that there is no memory buffer in the Naim system. It's just not possible to read the data directly off the disc and convert it in real time, as in that case you'd be relying on the speed of the disc motor being 100% accurate.

The only argument for why copies might sound different to original pressings is that the copies are somehow a "bit harder" for the player to to read, for example causing more error correction, which you might claim is audible via power supply loading or some other feedback/interference path.

A lot of very high performance analogue electronics is really black magic - no-one really understands it, even if there are models that explain the gross behaviours. I think that's why CD players can sound different when in theory they should all sound the same.

Posted on: 15 May 2003 by Thomas K

Alan,

"CD-R copies played on my CDS2 sound as good as the original so obviously any jitter on the copied disk is within the tolerance that the CDS2 will compensate for."

In a blind test, I can tell American and European pressings of many CDs apart on my CDS2, but it was much easier (with the exact same discs) to keep them apart on my old CDX. This suggests that it's not the actual data that's different, but something in the read-out process -- that would, if I understand the matter correctly, include CD-R related jitter problems (= the better the player, the smaller the differences between CD pressings/CD-R).

It would have been interesting to see whether they were bit-identical (I doubt it, but it would surely have caused "outrage in the world of engineering").

Anyone know what free software I can use to determine whether two discs are bit-identical?

Thomas

Posted on: 15 May 2003 by Twelveeyedfish

What does your degree have to do with it. I have a degree in electronics. Complete waste of time. Knew the electronics before I went in. Spent three years doing stupid maths. Apparently a class A amplifier has 4 components!

Decided not to go into electronics after that incidentally!

To Trevor, you can get rotation speeds very accurate - think of turntables. But since CDs are a serial storage medium, it is indeed completely essential to have a buffer.

It does depend on the copy method as to the quality of the output though. Nero does not do real copies. Clone CD is of the bit for bit type originally mentioned.

Andrew

diamonds - she'll pretty much have to...

Posted on: 15 May 2003 by coredump

IMHO the ripping process is where one should be very careful. There are free tools out there which can resolve timing problems using sophisticated algorithms. try "Exact Audio Copy"
(http://www.exactaudiocopy.de) for Win32 platforms and "cdparanoia"
(http://www.xiph.org/paranoia) for Unices. Both tools are - depending on the quality of your CDRom - slightly slower than ususal, but it's worth it.

Thomas, have you tried ripping the whole image again after burning and then md5sum it?

Best regards,

Oliver

[This message was edited by coredump on THURSDAY 15 May 2003 at 17:55.]

Posted on: 15 May 2003 by DynaudioBoy

"What does your degree have to do with it"

Sorry in a defensive nature I thought I would mention I had a degree so more people would think (stereotypically) I knew what I was talking about

and read the post, as it was my first.

The truth is I'm certainly not a 'no all', I only got a pass at degree level

I'm just trying to find all the answers I can out there, and finding this fourm full of people with them! a bit like naim really.

"Nero does not do real copies. Clone CD is of the bit for bit type originally mentioned."

Can you explain why nero does'nt make a bit for bit transfer as that is the only information on the disk, for it to transfer in the first place.

Posted on: 15 May 2003 by Twelveeyedfish

Off the top of my head, I can't remember the exact process but I can't explain why it doesn't do bit for bit copies. Perhaps something to do with earlier writer standards. CD cloning tools are certainly more fussy over drives now than tools like nero. Requiring explicit support. CD burning engines are pretty generic these days. Take XPs inbuilt support for example.

Gonna go finish listening to this Lp now!

tata
Andrew

diamonds - she'll pretty much have to...

Posted on: 15 May 2003 by DynaudioBoy

right! this is'nt aimed at anyone these are the facts

When you copy a file in a computer it copies the file exactly everytime if it did'nt then the copied file would not work it has to be bit for bit perfect.

When you copy a file from a CD it is exactly the same as copying a file from the rest of the computer.

When you copy a piece of software or write backup data files to a CD it does'nt do an approximation of your latest excel spreadsheet figures, or get some of the letters wrong in your document you just wrote, it copies the information!

When you copy an audio CD it's not audio it a load of numbers just like in your excel spreadsheet, it's not analogue waves it is a bunch of numbers than can be translated in to audio by taking a sample rate and dynamic range (44100hz samples a second, 16bits per sample) and reading the dynamic range value which represent the movement of the speaker cone after amplification.

So when you copy a CD, the copy is exactly the SAME! if it was'nt then CD would be a useless format for backup, distributing software AND AUDIO.

There is no such thing as a poor audio copy it's in your imaginations.

In audio no one knows the answers so the people with mose experience win, all the specs on speakers and amplifiers are a VERY rough guide to quality not how enjoyable or realistic the sound will be that is reproduced in the end.

Where as in computers there are answers and I know them, CD burners are in computers I know exactly how they work and how they talk to the rest of the system.

incidently why do CD Recorders in the audio trade have an analogue recording mode if the data on the source and destination is digital? What is the point in converting the already digital sound in to analogue then back again?

Sorry to go off on one, but I wanted to

Surely we are all after the same thing...knowledge and want to be taken seriously, no one will take someone seriously if they insist on believing in something that is'nt correct.

Thank you I'm off out now for a pint

Posted on: 15 May 2003 by Robbie

No difference,

Never heard a difference between copy and original, except sometimes a "tick" on the copy.
So I would say a copy is 99,9999999 accurate.

Regards,
Rob.

Posted on: 15 May 2003 by oldie

Ye god's and little fishes, when I said in the other thread that I couldn't tell the differance between my copies that I use whilst working in my garden, and the original cd's[and was basicly told by some of my more learned
Naimee's that I was a "deaf old prat"who shouldn't be useing a top end Naim system ]
I didn't think it would start all this.Now it apears that I might be totaly vindicated So I'll take my copies and walkman down the garden and enjoy the music knowing that I may not be after all such a sonically impaired old fool

can I claim a win for those of us that just enjoy the music, as apposed to those that seem to be more interested in how it works etc,

Posted on: 15 May 2003 by Twelveeyedfish

Reason for an analogue recording mode - our old friend SCMS!

As for comparing computers and audio, you shouldn't. I've worked with both. A computer is happy to wait a millisecond or two until data is re read, if a checksum is wrong, it tries again etc... so the computer seems to do the same thing but doesn't really.

Audio CDs don't have multiple speed drives, they need to get the data and they need to get it first time. The buffers and DACs depend on the order the data is in to be correct. If it is wrong, the error correction circuitry says so and it takes the wrong string of bits and changes them to an extrapolated value.

This doesn't mean the data on the disc is wrong. It means that given a reading surface or selection of bits, there is a higher probability the data will be correct if the surface is easy to get data from accurately and so on. This is the reason scratched CDs work. If I recall, CD specs. originally said that you could drill a 1/4" hole in a CD and it would still play... I am curious as to weather modern players adhere to this... to display the logo they should but it is a bit excessive! I dare someone to try it!

Andrew

diamonds - she'll pretty much have to...

Posted on: 15 May 2003 by Martin M

"So when you copy a CD, the copy is exactly the SAME! if it was'nt then CD would be a useless format for backup, distributing software AND AUDIO.

There is no such thing as a poor audio copy it's in your imaginations."

Well, actually some copiers (and copying software) have sample rate convertors in the 'copying-chain'. These can be in the chain regardless of whether they are needed or not. If they are in the chain they can change the timing and value of the digits (that's there job) and so introduce jitter. In that case, they would sound different to the original. A straight clone should (or rather will) sound the same as the original providing the CD and the clone are not producing different uncorrectable errors on playback.

"Audio CDs don't have multiple speed drives, they need to get the data and they need to get it first time. The buffers and DACs depend on the order the data is in to be correct. If it is wrong, the error correction circuitry says so and it takes the wrong string of bits and changes them to an extrapolated value. "

This is wrong. The FEC and interpolations are always calculated and no matter the data values. Furthermore, there is a fixed propergation time through these (and the various other mechanism that knock some codespace into CD). The use of a small (but correctly specified) buffer memory at the end of the chain will remove the rest of the jitter. Of course, you can re-introduce the jitter reading the information out of memory but that's a different story.

Posted on: 15 May 2003 by john rubberneck

Just my 2 penneth

It’s my understanding that CD’s use a different file structure to data and herein lies the problem with copying them, whilst it is possible to copy data with bit for bit accuracy it is not so with cd, also a carrier is needed for the digital information rather like the one on tape, video,fm,telephone backbone etc in fact in the case of cd coming of the opu it looks not unlike a three fase helix (analog), and uses a complex reading code to decode the pcm, which I suppose to be fair for a code that dates back to the 1930’s I think, doesn’t do a bad job, as an example of other codes in particular mp3’s for a friend I copied a mp3 over the internet form someone, it came from the us ( I live in the uk ) it’s origin was a recording live of his boys band on a cd , then converted it to a wave file and burnt to a cd, so it’s path had been live recording, cd, mp3 , mp3 over tc pip, mp3, cd, I gave it to my colleague who put it on the cd player in his car, it lasted about 4 seconds before being thrown out the window in discuss , bloody ungrateful I thought, it sounded ok to me considering , the point about mp3’s was only to illustrate how versatile they are, I find it strange that so many people hate them so much when we have pcm ,we certainly wouldn’t have net music, what I do find incredible is that we are expected to take on another reconstruction of it ,as to the title of this post I total disagree.

Stuart

Posted on: 15 May 2003 by Twelveeyedfish

PS - since our posts overlapped I needed to add it...

I'm an electronic engineer! It's my job to know how it works. And my interest.

More a win for those who found Naim! I will join you in playing my copies!

Andrew

Actually - for the record, a copy of a cd made using one of the first generation of audio cd copiers is definitely (in blind tests) easy to tell apart from the original. Newer copies are not! I generally can't be bothered trying it with computer CD-Rs. Not worth it!

diamonds - she'll pretty much have to...

Posted on: 15 May 2003 by Martin M

Sorry Twelvety, I mis-read your post, no offence meant.

Your correct statement and my correct answer to a completely different point are below. BTW I think most CDs have very few uncorrectable errors and so the interpolators don't get excercised very much (indeed I think they switched off in the CDS-1)

BTW May I add a 'Aaaaaaaaah' in a Peter Griffin voice?

"Audio CDs don't have multiple speed drives, they need to get the data and they need to get it first time. The buffers and DACs depend on the order the data is in to be correct. If it is wrong, the error correction circuitry says so and it takes the wrong string of bits and changes them to an extrapolated value. "

This is wrong. The FEC and interpolations are always calculated and no matter the data values. Furthermore, there is a fixed propergation time through these (and the various other mechanism that knock some codespace into CD). The use of a small (but correctly specified) buffer memory at the end of the chain will remove the rest of the jitter. Of course, you can re-introduce the jitter reading the information out of memory but that's a different story.

[This message was edited by Martin M on THURSDAY 15 May 2003 at 22:10.]

Posted on: 15 May 2003 by oldie

Holy Mackerel!!!! I didn't realise that all this went on when I pressed that little button that say's play, I'll have to be more careful
in the future
all the best Andrew

p.s Ive also worked with degree students at the Uni. of Brighton, so I know how knowledgeable they all are

Posted on: 15 May 2003 by coredump

DynaudioBoy, I don't know what your profession is, but I hope it has nothing to do with computers :-)

Normal (data-) CDs have got a valid file system of some sort, which is mountable. As soon as that (hopefully) the operating system sorts reading and writing out for you with some techniques to make sure the data in your memory is the same as on the disk (CRC-checks for example). up to here your statement is perfectly valid.

The CD digital audio format, however, does not have a proper filesystem, and it does not need to. The tracks are written sequentially down the track (yes, a CD has got one track, like a record), you have a TOC at the beginning (containing time-based information) and that's it.

And because of that CDs are not mountable. BUT, however, you could read the TOC, jump to the beginning of the wanted track, accelerate the drive to the speed you want and try to catch the stream that is now coming over the bus. The trick here is to stay in sync with the signal, that means: if the CD drive sends something like
-1-0-1-0-0-1-0-1-1-1-1 and because of timing problems you read
-1--1-0-0--0-1-1-1-1 obviously some data is getting lost.

If you don't believe me, please try and google JVs opinion on this matter. And ask yourself why Naim never produced a CD-Player with a separate DAC.

Posted on: 15 May 2003 by Tango

I could have sworn that sometimes my CD-R's seem to sound better than the originals that they were copied from.

Posted on: 15 May 2003 by John K R

Twelveyefish is completely right when he says Nero does not do 1-1 copies and Clone does. When copying PC games with Nero they rarely work, with Clone they work every time. Similarly when friends try to copy enhanced CDs or CDs with copy protection using Nero (or some other software) they fail. I can honestly say I have never produced a coaster with Clone. In the world of game copying (where copy protection and sub channel data is common) Clone is used almost exclusively, because it does 1-1 copies.

Now all of this does not prove or disprove that there is any audible difference, but you don’t get an exact copy of the original without Clone (and perhaps now some others)
John.

Posted on: 15 May 2003 by Minky

Does this mean that because I :

1) Was suprised at how much better a bought copy of the new Lucinda Williams sounded compared to my pre-relase pirate (Original > computer HD > CD-R) which incidently skipped a bit.

2) Don't like the way copy protected disks sound on my PIC upgraded CDS2 (I guess it could be the recordings but 4 out of 4 is almost 100%).

I am completely insane ?

Posted on: 15 May 2003 by Greg Beatty

A guess about why CR-Rs can *sometimes* sound better than the original.

The CDR's that can sound better, and, incidentally, the kind a friend who tested several kinds with his CD 3.5 found to sound best, are the ones that have a green surface. TDK used to be this way, don't know if they still are.

The green surface can reduce read errors compared to the original (non-green) CD.

Oh, another reason is if the original CD is badly scratched - say a flea market special (I have several of these). The copy will be clean and can be read with less error correction.

- GregB

Insert Witty Signature Line Here

Posted on: 15 May 2003 by Minky

So the copy process can get a read error on the original disk, figure out what it was supposed to look like, and fill in the gaps such that the copy is closer to the master disk than the original ?

Posted on: 15 May 2003 by Greg Beatty

Hey Minky -

OK - I am no expert in this area so this is conjecture at best. Perhaps a contributor with more direct knowledge of how copying and music playback in a CD player works can comment.

The idea is that when a CD player has to error correct, the sound quality is degraded. Now, when a copy program encounters a scratch on the CD, what does it do? Can it re-read until it gets the bits and then make a clean copy?

And if the CD player error corrects a certain percentage of the time and this is reduced by inserting a green disk into the player, this would have the same effect.

AudioPrism make a thingie called the CD Backlight that glows green. You place it on top of a CD in your CD player. It cleans up the sound a bit and gives a little more omph in the bass. My wife hears the difference and usually uses it.

- GregB

Insert Witty Signature Line Here

Posted on: 15 May 2003 by Twelveeyedfish

Funny you should say that Mr Beatty - my first Audio CD-Rs are infact green dye based. I'm brought to ressurect images of spectra now to think why that may happen but frankly it's five in the morning... I woke up, listened to Tubular Bells and now was planning to sleep but couldn't resist a look here!

Another thing, if I recall correctly, don't Audio Note DACs use no filtering and no error correction circuitry at all. I can't remember off the top of my head what actual filters are in the DAC itself - I used Philips 1307s in my demonstration CD player (hand soldered!) and I'm sure that they mentioned internal filtering. I don't know what the Naims use - sound too good to care! Still, it means that there's clearly not much gain to be had from error correction at all, although not the same sound as Naim, the output still sounds kinda like the song!

I think the effects of early morning have made me digress a little. It contradicts what even I've said earlier that last bit does! I suppose this brings us to the SNR of the Transport!

Touche!

Andrew

PS - thanks for recognising where the signature came from! Series 2 - Peter Peter Caviar Eater!

diamonds - she'll pretty much have to...