Absolute Phase???

I'm not so sure if this question belongs in this area of the forum, so please forgive me if I have posted in the wrong place.

I recently read about absolute phase in Robert Harley's The Complete Guide to High-End Audio. The book gives a basic and brief description of the concept of absolute phase, but I was hoping that someone more knowledgable than myself could explain it in greater depth or direct me to a resource that could.

Thank you.

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Originally Posted by Shwamdoo

I'm not so sure if this question belongs in this area of the forum, so please forgive me if I have posted in the wrong place.

I recently read about absolute phase in Robert Harley's The Complete Guide to High-End Audio. The book gives a basic and brief description of the concept of absolute phase, but I was hoping that someone more knowledgable than myself could explain it in greater depth or direct me to a resource that could.

Thank you.

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Absolute phase is an ideal that is very difficult to achieve. I have not read Robert Harley's guide but I am a fan of his writing and reviewing. There are several things that can affect absolute phase and that can be the recorded material itself. Individual components can invert phase and of course components use to have a switch to invert phase. In speaker design sometimes the tweeter can be wired out of phase with the woofer and of course absolute phase can not be achieved. If I remember correctly you wanted the speaker cone to move in the same direction as the microphone diaphragm did while the recording was made. When it was mostly an analog world I knew people who would switch either there leads to the phono cartridges or reverse the polarity of their speaker cables. Running the negative output to the positive speaker input and vice versa. They would then mark the records as to which way they should be played. Not much music listening was happening rather it was in phase or not. I hope this does not muddy things further.

OK...I understand what absolute phase is. But I don't understand why recordings would be done with reversed phase. Robert Harley said in his book that about one half of recorded music is done in reversed phase. Is this true with all forms of media, or just with vinyl?

Thanks again.

Quote:

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Originally Posted by Shwamdoo

I'm not so sure if this question belongs in this area of the forum, so please forgive me if I have posted in the wrong place.

I recently read about absolute phase in Robert Harley's The Complete Guide to High-End Audio. The book gives a basic and brief description of the concept of absolute phase, but I was hoping that someone more knowledgable than myself could explain it in greater depth or direct me to a resource that could.

Thank you.

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OK. Sound waves alternate between pressures and rarefaction. Suppose a pressure hits the microphone and part of a recording. When it comes out of your speakers, is it going to be a pressure or a rarefaction. If the former, the polarity is correct, if a rarefaction, it is not. So, if the polarity is correct, then the condensations and rarefactions in the sound waves occur as they did in reality. If not, then they are played back opposite to what they were in reality.

There are many things in between, in the recording chain and the playback chain that can invert polarity. The real question is whether one can hear the difference. The answer seems to be on the whole, no. There are been test signals which enable people to hear when the polarity is inverted but for the most part, anyway, not on music. The results of the old ABX tests still indicate the situation pretty well:

http://www.pcavtech.com/abx/abx_pola.htm

Some more recent information comes from the debate between Arny Krueger and John Atkinson as part of the Home Entertainment 2005. Far into the debate, they have an exchange over the audibility of polarity differences. You can download the debate from the link in Jacob Victor Serinus's somewhat biased report in Stereophile:

http://www.stereophile.com/news/050905debate/

Somewhere near the end of the debate, Arny Krueger maintains that in a low distortion system, polarity reversals seem to be even less audible.

There was something on the audibility of polarity reversals in an article on the Audioholics.com site but I can't locate it.

On my previous D to A I had a phase inverter switch. When I operated this switch on some recordings there was a noticable difference mostly on guitars and some other instruments (a harp if I recall).

Although there was a audible difference, it was impossible, for me at least, to identify which was correct. I tried it both ways for long sessions to see if there was any affect on fatigue for example. Never worked out which was correct and finally left the switch in the inverted posistion for years (my system had one inversion so in theory with the switch "inverted", it was now phase correct).

Maybe on a megabuck system you could work out the correct setting, my stuff isn't junk and I couldn't. I wouldn't worry about it.

but one of the reasons that correct absolute polarity is important (provided that the recording was done correctly with all mics and processors in correct polarity) is that music waveforms are asymmetrical. that is the top half of the wave as displayed on an oscilloscope is quite different from the bottom half.

therefore, the compression part would seem to carry the forward part of a transient and vice versa for the rarefaction.

i too have heard a cdp with phase reversal, remote at that, and trying it just to see, one way sounded right and the other sounded not quite as right. i had no expectation and i didnt run out and buy a device to do this, nor do i run to reverse my speaker polarity BUT it would be a nice remote feature to have, dontcha think?

this isnt snake oil nor smoke. its a real effect that can add to the realism of a recording being played back and its free if you want to do it physically.

more audible with some instruments than with others IME. Instruments with highly asymmetrical sound waves, such as brasses, are more susceptible to AP errors than are symmetrical instruments such as the strings IME.

Good luck however in ever determining the correct phase for most recordings as there are so many connections in a chain that can be inverted in relation to each other that I no longer care to try to set phase for the overall recording. It is probably impossible when more than one mike is used.

Some human voices will sound better out of polarity, especially if there are any class A amps in the circuit. They will simply have sharper negative peaks than positive, and class A will do better with the sharper peaks in the positive going domain. It's an old school broadcast radio trick. ;)