[clarkjohnsen]

Philip wrote: Let me know how to do that (find the "right" polarity in a useful way).

Let me, a newbie, jump into the ring. My attention was drawn to this discussion by a friend who knows of my abiding interest in the topic. Let me first introduce myself as author of a book called The Wood Effect: Unaccounted Contributor to Error and Confusion in Acoustics and Audio. And I certainly do see a lot of confusion here! Perhaps to start, a definition of terms would help. The abstract to The Wood Effect puts it this way:

"Masked by random combination with other distortions in the music reproduction chain, an unsuspected major contributor has lain hidden: Aural sensitivity to ‘phase inversion’ — the Wood Effect.

"Musical instruments normally create compression wavefronts. Electronics, however, often invert that natural, positive polarity to unnatural, negative rarefaction, thus diminishing physical and aesthetic impact. The term Absolute Polarity uniquely describes the correct arrival to the ear of wavefronts from loudspeakers, with respect to actual musical instruments.

"Wrong polarity, when isolated, is obvious to all. Its present neglect results from habitual disregard for phase response, especially in loudspeakers."

Yes, loudspeakers – those nasty incoherencers with high-order crossovers -- mask polarity with hundreds of degrees of phase distortion. No wonder people question the idea of a mere 180 degrees being audible. But audible it is, on a minimum-phase system.

That assumes, however, that the recorded material is not itself phase-gemischt. In pop music one cannot trust the source to be phase coherent, but take any minimally-miced recording -- or even better a true monaural recording -- and the phenomenon will leap out at you... anyway on a minimum-phase loudspeaker.

Considerable confusion arises from not distinguishing between "absolute polarity" and simple "polarity". In most instances the latter term is correct. Equipment (electronics, mics, speakers) possesses only "polarity" -- and that means either "inverting" or "non-inverting". Whichever way a signal is inscribed onto a disc or committed to tape (and note well, there are no effective standards for any of this), it still retains all other audio properties. Whatever the reproducer's native polarity (and it could go either way), the recording may still be heard entirely properly, if correction, if needed, be made.

The question arises, how may this problem be accounted for in mastering? Answer: Not easily! Material has been created in environments where no consideration for polarity has prevailed, apart from assuring that mics have been aligned, if we're lucky. But inversions can creep in at consoles, peripheral gear, recorders etc. etc. If the mastering engineer is to do anything at all useful, he must determine the polarity of each cut and align them to one way or the other. Keep in mind, there is no "right" way at this point, and a study shows that recordings (CDs, LPs, tapes) are split 50/50 -- sometimes on each disc!

One of the most nonsensical statements I read here goes, "Telarc always made sure that their bass drums would produce an outward-going woofer [excursion] for most impact." And just how were they able to assure this?

That question is unanswerable, if you've been following my argument. Likewise, nothing the mastering engineer (or any engineer in the chain) can do will produce the desired polarity result at listeners' ears. Only the listener, sitting in acoustic space like the musical instruments themselves, can make "absolute polarity".

Absolute polarity, once learned, like bicycle riding can never be unlearned. But generally speaking, one must listen for it and "throw the switch" accordingly. Granted this may become tedious, but what else can one do when our mastering engineers continue to create product with both polarities, sometimes even alternating from cut to cut. (And what's up with that?)

So far as I know, only one device on the market attempts to determine polarity in acoustic space, the SMART System 2000 Sound Check from Smart Cinema Sound Products. I have used it and agree with its readings. Often, however, as you understand, a recording is so gemischt that no such determination is possible.

Hope that helps. The Wood Effect was published back in 1988 and contains over eighty references to polarity in the audio and acoustic literature, besides (if I may say) a wealth of corroborative information. Its author (yes, myself) had hoped that a book would settle the matter once and for all, but controversy and misunderstanding still flourish unabated.

clark