really interesting McWilliams; Thanks
So take Decca which still makes recordings; lets say the engineer made a deliberate parity reversal. Then you should not want to reverse it, if you wanted to hear how it was supposed to be listened to.
Or if there was a basis (or even a risk) of parity reversal affecting music quality, I'd think that some of these big classical companies, recording studios, producers would have already switched their equipment. Lets say they did, but as KStuart brings up can't just say that all Archiv recordings after 1992 are reversed or vice-versa
Or the engineers and musicians/producers/recording studios that approve the masters either are convinced that their is no audible difference, and like their master. Then shifting the parity would be like putting the loudness on or boosting the eq, a subjective choice on the listeners end. Why not. JRiver can do that. But then wouldn't it be no longer bit perfect playback, sensu stricto?
My point was that it's unclear how anyone is successfully testing to see if a recording has it's "polarity reversed" at step one. Because it's very hard (or impossible depending on your view) to tell if the polarity of a recording is reversed or not, people look at a number of factors to assess the "polarity" of the recording. The most popular way is to look at whether a drum hit creates a positive or a negative pressure wave. If the drums were deliberately recorded with their polarity opposite the rest of the music and you only look at the drum hits to determine polarity, you could come to the conclusion that the polarity of the recording as a whole was reversed when in fact only the drum hits were recorded with reversed polarity.
If you then flip the polarity switch on that recording, what's the effect? The drums become positive and the rest of the recording becomes negative, but their relative polarity remains the same (they're still 180 degrees apart). That means that it shouldn't sound any different unless you believe that absolute polarity of the whole mix makes a difference. If you believe that absolute polarity makes a difference, then you've goofed it up and flipped the whole thing because you were only looking at the trunk of the elephant and concluded it was a snake.
I can't hear the difference when the absolute polarity of the entire mix is flipped, and I'm not aware of any studies suggesting it's audible. But if it is audible, then you'd need to have a good methodology for determining whether polarity is correct or flipped on a
recording by recording basis.
And kstuart is 100% right, polarity of a studio's output will vary for a lot of reasons (some resulting from equipment, some resulting form personnel). It's a little like wiring a power socket; the right prong is supposed to be hot, and the left prong is supposed to be neutral. Only about 60% of the installed power sockets I've tested were wired that way. But IME most equipment* doesn't really care which is which as long as it has one of each. Recordings can have "correct" or "inverted" absolute polarity, in part because for the most part we can't tell which is which (we can, for the most part, only hear differences in relative polarity within the mix).
*Some equipment cares, and cares a lot, and a reversed polarity socket can pose a serious safety hazard, I just mean that most equipment will turn on and function normally, not that it's a good idea.