Friday, July 7, 2017

Holt on Polarity

Stereophile has resurrected an oldie from J Gordon Holt on Polarity originally published in 1980.  He is saying that you only hear it when you have asymmetrical non-linearity.

This generates a lot of flack from commenters.

I think Holt is correct in a limited sense.  When people claim to hear differences because of absolute polarity, it's almost certainly one of these (and they are not exclusive):

1) their imagination, because of sighted and uncontrolled testing
2) non-linearity in reproduction

The third possibility--actually reliably hearing polarity differences--occurs only in limited cases:

1) asymmetrical test signals designed to make it more obvious
2) Solo trombone or the like
3) Headphones plus either of the above

That is essentially what the premier study on polarity by Lipschutz in the 1980's determined, using pulse coherent Quad ESL-63 speakers and headphones.

Holt wasn't using test tones or very specially selected music, so his results are quite reasonable, and shows his fundamental honesty, and the relative inaudibility of polarity.

I had my own brush with this recently, first I correctly heard something which turned out to be polarity, and then I thought I heard it again and didn't.

Even if relatively inaudible, a good recording or system should try to get it correct, to the degree it is easy to do so.  If this means reversing speaker cables on each track of a recording...I'd say forget it.

Zero phase shift would be nice too, if not so impossible.  Tradeoffs between lumpy frequency balance or phase shift generally favor prioritizing the frequency balance, and that's why we have things like crossovers and multi-way speaker systems in the first place.

Meanwhile the idea that recording industry inverts polarity as a way of ripping off the public...sounds pretty preposterous.  If ever wrong, one would first suspect error rather than design.  There are far more obvious ways to alter recordings for popularizing and/or degrading the material, such as in frequency balance and dynamic range.  Polarity adjustment might be made simply on the basis of which sounds better, which could simply be random chance because of the difficult of correctly hearing it.  Given that such judgements are possible, and even occasionally used, one would expect error to creep in, even if technical connections and systems were always perfect (and, that's a stretch too).

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