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[Justice C. Bigler]

A phase shift requires delaying the time signal .  There is no way to make a signal come out before it comes into a system in the real world, so phase shifts in audio must be accompanied by time delays until we figure out time travel.

So, once we get the time travel machine working, we can insert it as a plug-in on a channel strip and go back in time to lower the fader for the channel to eliminate the feedback before it happens in the first place right?

[David Simpson]

So, once we get the time travel machine working, we can insert it as a plug-in on a channel strip and go back in time to lower the fader for the channel to eliminate the feedback before it happens in the first place right?

Yes, but the phantom power on the time travel channel will need to supply the required "1.21 Gigawatts" necessary for time travel. 

~Dave

[Frank Koenig]

Let me put it this way. In order for the math to work you have to treat a polarity inversion (realizable), as well as a Hilbert transformer (which can only be approximated), as a frequency-invariant phase shift. Don't have much use for math? Fine. But realize that most of the toys we enjoy so much were designed by folks who use a lot of math to do so.

Furthermore, causality has nothing to do with it. We use non-causal approaches to problems all the time. They are implemented by a time-limited non-causal system plus a processing delay, making the whole kit causal. No time travel required.

The problem here is one of context. When you're in the trenches trying to explain what the button at the top of the channel strip does it's OK to say that it inverts the polarity without affecting the "phase". Probably a good thing, actually.

If, on the other hand, you're trying to design FIR filters to correct linear distortion in loudspeakers and you're up to your ass in transforms, you'd better get all the minus signs right. If anyone wants to see an example in the literature of polarity inversion treated as phase shift I just happened to run across one. "Phase Distortion and Phase Equalization in Audio Signal Processing -- A Tutorial Review" D. Preis, J of the AES, vol. 30, No. 11 1982 November, p776, just after eq. 16.

--Frank

[Ryan Tolzmann]

I think keith and nathen explained the theory behind it a lot better than I did.

I myself have never sat down with the time to experiment with it to get conclusive results.

its good to know the thoughts and reality of what is actually happening. Since I didnt go to school for audio, I learn through reading on my own and discussing with other engineers.  So I really appreciate the responses and this site in general.

[Ryan Tolzmann]

Oh definitely didnt see the 2nd and 3rd page since im on mobile... I have some reading to catch up on..

[Tim Padrick]

A bunch of people are standing in line for a show.  A phase shift would change how far apart they are.  A polarity reversal would stand them all on their heads.

[Kevin Maxwell]

I use auto mixing for the dialog parts for all of my theatrical shows nowadays. And I don’t want to go back to the old way.
 
I spoke to Dan Dugan at the AES expo in NYC 2 weeks ago and if I am remembering the conversion correctly the recently made versions do not have the music mode in them. And I got the feeling he is really pushing his units as speech only devices.

If you are having problems with gain before feedback for the singing parts then that is a matter of how the system is setup and tuned. I have some techniques for that if any one wants the information let me know. But if you search for my posts on the subject I have probably covered it all on here at some point.

If the problem is the way it sounds when 2 actors are really close to each other, sometimes the phase/polarity switch will change the way it sounds, sometimes for the better and sometimes for the worse. It is very inconsistent even within the same song due to their inconsistent relative positions to each other. Usually the only way to deal with that is to be on the ball and be constantly changing which mic is up more then the other. I have many times found that I get a better sound using just one of the actors mics for picking up both of them. But I have to be ready to bring them both back up when they move away from each other.   

[Chuck Simon]

"I think the use of the term "polarity", and its absolute separation from the concept of phase, has become a bit dogmatic on these forums."

There's my "BINGO" moment!

[kristianjohnsen]

"I think the use of the term "polarity", and its absolute separation from the concept of phase, has become a bit dogmatic on these forums."

There's my "BINGO" moment!

Agreed!

[Mac Kerr]

"I think the use of the term "polarity", and its absolute separation from the concept of phase, has become a bit dogmatic on these forums."

There's my "BINGO" moment!

Agreed!

What is it you think is dogmatic? They are absolutely different things. The electrical inversion of signal via the Ø button on a console has no impact on the phase of that signal. It is very similar to the 2 legs of a 240V single phase power system in the US. The 2 hot legs are out of polarity with regard to each other, but they are in phase with each other.

When you introduce a filter in the circuit, for instance an eq, you change the phase, but not the polarity. When you change the relative positions of 2 speakers passing the same audio, you change the phase relationship between them without changing the polarity. When you change the delay of 1 of the speakers relative to the other you do the same. When you change the polarity of 1 of them you change both the polarity relationship, and the phase relationship because of the 2D or 3D geometry of the summation of the signals in space, but considered separately the 2 signals will not be out of phase, only out of polarity.

The reason this difference is so often pointed out (maybe excessively) is to make it clear that there is a difference, and that phase is a more complex concept, and behaves differently than polarity.

Mac

[ProSoundWeb Community]