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Author Topic: Reversing the phase of mics for live gigs  (Read 3119 times)

Kim Watson

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Re: Reversing the phase of mics for live gigs
« Reply #10 on: January 26, 2008, 07:07:39 pm »

Hey Jeff

When talking about 2 mics on the same drum and reaching for the wrongly labeled "phase" button. the effect isn't a 180* change... its a polarity flip. (P to P or P to N like you say!) so even the delay time between the 2 mics will remain the same. all it will just change the polarity of the wave form making it interfere differently. and sound differently

Phase has a Time component and is corrected by delay. New digital consoles have the capability to align all the signals in time.

Now how is this going to effect everything in a small room. End of the day its a huge compromise..... as you know if you have 2 mics picking up the same source and one is further away you will get comb filtering. same with hearing sound from FOH speakers, and the bounce back from the back wall of the stage from the monitors, a polarity invert(on monitors) may do the trick to make FOH sound thicker.

It all depends on the situation. room size etc. Its all a case of spotting what is causing the issue and how much you can correct for it.

Delaying the PA to the back line may Reduce a 2nd layer of room reverb (since both signals arriving at the same time or close will decay at the same rate). Clearing up some of the mess and interference.

Whats really gonna cook your noodle is when you think all the backline etc you have mic'ed are all getting picked up by the vocal mics as well and fed back in to the system for another layer of comb filtering too!

We work in an industry where we converge towards perfection but can never quite make it. We just have to do the best for the situation possible!

Like everyone says Try it! What works in one venue or room may not work in another. This is why the Try it and see is pre programed!   Very Happy

lastly its all down to the ears....Listen and decide what sounds best! Good luck!
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Have a great day!

Kim Watson
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www.polarisaudio.co.uk
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Tim McCulloch

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Re: Reversing the phase of mics for live gigs
« Reply #11 on: January 26, 2008, 07:31:50 pm »

Jeff Hague wrote on Sat, 26 January 2008 17:22

Tony, so the mic itself produces positive voltage when the diaphragm moves toward the back of the mic? That would make sense but Ive never thought about it until now and never read anywhere that it is the case - thanks!
It may be subtle but there is definately a difference when top & bottom micing a snare. I rememebr the first time someone showed me their routine - 2 mics, neither reversed, drummer banging away while a tech moved the 2 mics until it sounded worse than an AM radio. Then he hit the "polarity" (phase!) button on the bottom mics channnel strip - damn! It was simply amazing!

When he was moving the mics, he was looking for the greatest "null" effect and was doing it by changing the *time* relationship between the mics.  When he found the greatest cancellation at the freq he wanted, he then inverted the polarity.  He could have moved the mics until he found the tone he wanted without an inversion, but it's easier to hear cancellations.

BTW, "try it and listen' *should be* the stock response here.  Not picking on you, but in general we get a lot of "what if" questions where the poster would be better served by gaining listening experience.  Ultimately, that's what matters... what we hear.  It becomes the basis upon which we make system optimization and mixing decisions.

Have fun, good luck, and keep experimenting.

Tim Mc
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