Home Digital Drive

Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it.

RE: Response #2 -- the discs

"Test discs -- What assurances do you have that any one of them is correct, or consistent with others? (And, What is correct?!) In a test conducted last year among a group of six discs with polarity test impulses, guess what? Yep."

It would be helpful if the miscreant test disks could be identified by manufacturer, model number and if possible pressing numbers.

The redbook standard describes how the pits on the CD map into digital 0's and 1's and how these are organized into the directory and the audio track. There is no way a competently designed CD drive could get this mixed up and still operate at all. Same for CD burner. The audio samples are 16 bit numbers. They have no polarity until the DAC interprets them, at which point the Red Book standard applies, which specifies that the 16 bits are in "2's complement arithmetic". This is a mathematically defined format.

If one uses any competently written audio editor one can produce a WAV file that consists of the same 16 bit 2's complement samples. If this is burned it will then produce a disk that contains the same samples, as can be demonstrated by reading back the samples and verifying that the bits are unchanged. This process does not involve any interpretation of polarity, it is just a matter of processing the bits. If the drive used is operating incorrectly the verify process will fail.

That does not mean that there aren't defective test disks out there. But if there are, then they can easily be caught and the defect verified. Incidentally, if one is so inclined one can sit down with a microscope, pencil and paper and a copy of the red book specification and personally verify whether a test disk has the correct polarity. (Tedious, to be sure, but possible.)

"Many, probably most, CDs come with a willy-nilly mix of polarity cut-to-cut. This can be, and has been, proven."

I have yet to have seen the evidence. Most CDs are made with one set of equipment at one venue and there is no possibility that individual tracks would have different polarities unless the engineers deliberately tampered with polarity on a track by track basis. This strikes me as extremely unlikely, given that I've never heard of a mix or master engineer talking about doing this. There may be one or two labels or engineers that do this secretly, but that this is happening generally seems like a conspiracy theory.

More likely, the polarity of the recording itself is consistent track to track on one CD (or multiple CDs made with the same gear) but due to certain acoustical quirks in the recording process certain tracks sound better to certain listeners on certain systems when played back with reverse polarity. There are various technical reasons why this might happen having to do with the difference between polarity on transients and the impact of even harmonic distortion. I have seen no intelligent discussion by any of the advocates of polarity that addresses the difference between polarity on transients and polarity on asymmetrical steady tones, and indeed I suspect that most polarity pundits lack sufficient technical knolwedge to appreciate the issues. I may well be wrong on this point and if so, I trust that a knowledgeable polarity pundit will set me straight, hopefully by providing references to published material.

Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

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