Bit perfect copies

No such thing as bit perfect. To make my point Stereophile had an article about BMG's quality. As you may recall, BMG remarkets CDs to clubs. Stereophile did a comparision between the original CDs from RCA, Mercury and other companys and the BMG pressings. Result was the BMG CDs were digital perfect but didn't sound as good.

To cut this long story short. The bits layed down were identical as will be those you make at home in general. The problem is the timing. The jitter and phase of the bits as they clock into the D/A add distortion to the sound. CD burners are not as good as BMG's so you will be degraded even more.

How do you overcome this? You don't.

I don't think I follow what you're saying - clocking the bits (samples) into the D/A comes well after the reading of the disc, so how does the source (CD vs. CDR) affect the quality at the point of putting it into the DAC? Are you suggesting that a CDR gets read "wrong" despite being bit-perfect where the CD gets read "right"? I also don't understand the concept of "bit phase". Would all these issues go away if the whole CDR was read into RAM before playback began?

I'm very open to the concept that CDRs are somehow inferior to the original CD, though it hasn't been my experience and runs counter to my technical understanding (which undoubtedly could be enhanced). I don't think Stereophile saying CDRs "didn't sound as good" really establishes much as there is an inherent bias there - if it really is possible to make 50 cent copies of CDs that are indistinguishable from the original (using a cheap computer no less), that's not good for Stereophile's business. I'm not saying their viewpoint can't be right, just that it doesn't mean much coming from them.

To answer the original poster's question, I'd use a computer and some easily obtainable freeware or shareware to make the copies. Cheap, easy and effective. -Kirk

Kthomas I agree with you about cheap and effective. But not perfect. There is jitter introduced at all stages of the digital to analoge process. For the digital to digital I was not referring to the error encoding of the original being changed. I'm actually talking about clock in the CDR that governs the placement of the copied bit on the cdr media. When it is not dead on perfect (parts per billion or less) The the decoded signal on playback has phase errors in the analog signal. Ideally even if you had an imperfect clock that would repeat its errors reliably and it was used to burn the CDR and play it back you would have no error in phase in the analog output. But you don't.

Also one other issue. No player reads every bit perfectly from the original play. That's why we have error encoding built in to the process. So you have to read every bit perfectly (typically 700K of them) and then place them back on the CDR without a signal one out of place. If the CDR has a flaw in its manufacture or the laser varies in intensity or location.//error.

I enquired with Linn about problems I had been having while playing CDR's on my Genki. Certain CDR's (roughly 25% of my 'burned' CD's) suffered from occasional background shuffling sounds as well as occasional but very prononced ticks and crackles. Sometimes the CD would hick-up (stop playing mometarily) - at which point the recording would resume playing smoothly again. In the worst cases certain tracks wouldn't play at all. These problems never occured with CD originals - except in one instance when a 'real' CD suffered from the same shuffling background noise. This problem was immediately rectified after I blew into the CD player drawer - presumably dislodging a piece of dust from the laser lens.

My question to Linn:

Hello, I own a LINN system (Wakonda/Kudos, Keilidh, LK140, Genki) - my question is regarding the Genki. It has difficulty reading certain CD's ('burned' copies)- that my old sony can read without trouble. At times I must try skipping ahead in order for the cd to play at all. I tried cleaning the laser - it seemed to help a little. *Most* cd's play without incident. I would appreciate any advice regarding this condition.
Sincere thanks, - Me -.

Linn's response was as follows:

"The Genki CD player may or may not play CDR's and CDRW's because of the following reasons:

1. Many 'domestic' CDR machines have copyright protection coding (SCMS) onthe digital input , so when you copy commmercial CDs the only way to do it is using the Analogue output of the CD player to the Analogue input of the CDR recorder. This will result in degradation because of passing the signal through the D-A and A-D converters in the two machines.

2. There are several stand-alone CDR recorders which will accept digital inputs, but which also accept 48kz digital sources as well as 44.1kz. They do this by interposing a 'Sample Rate Converter' in the signal path, and while this is a good way of getting 48kz audio on to CD ( which have to be 44.1kz ) normally these machines leave the Sample Rate Converter in-circuit while accepting 44.1kz digital audio. This means that the copy will not be a bit-for-bit 'clone' as one might expect and as a result there may be some degradation in quality.

3. If the copy is made using a CD-copying package on a PC, many of these are very poorly implemented, which again means that the copy will not be a bit-for-bit clone, the most frequent problem being that the 'dither' information in the LSB is lost or corrupted. This leads to a loss of
detail and ambience.

4. If none of the above is the case, it may simply be that the physical qualities of the disc ( transmissiveness / refraction of the Polycarbonate of the disc itself, concentricity of the disc, reflectiveness of the metallised layer) are inferior to those of the original pressing. This can sometimes affect sound quality, if only because the CD player will be working harder to decode it.

Please feel free to contact me at Linn Customer Services if I can offer any further advice or assistance."

Best regards,
Richard Johnson

Richard - that's an interesting response. Thanks for sharing it with us. While the audio CDR components appear on the surface to be a really convenient way to make copies, I find it's at least as easy and considerably more flexible to make copies on my PC and that's what I would recommend to anyone wanting to make copies. I have never had a single problem with playback of a CDR that I've made this way. Occassionally, I have a problem in the copying process, but that's immediately flagged and I start over. Once made, though, playback has always been flawless - none of the noises you describe. I play them back in either a Sony ES changer or a Sony DVD-S7700 DVD player, digital outputs in both cases.

One of the advantages to this approach too is that you can verify a bit-perfect copy. Once you've done that, the first three of Linn's responses are off the table and you'd be left with the fourth as a possible answer if you continue to have the problem(s).

I use a fairly recent Dell setup for copying and Memorex CDR blanks. -Kirk