audio polarity/ phase reverse problem?

[Nate Clapp]

I know build 16 was supposed to fix "audio polarity problem" but here I am on build 17 and I still seem to have it. I have old audio board, and actually most of the stuff my camera has done has been MOS or dual system sound, and when they used in camera stuff they figured out they had to phase reverse one channel and they were good, but I am now aware that my stuff is out of phase. What does it mean? record two identical tracks of audio (doesn't matter which 2 of the 4 inputs on camera) and play them back in FCP or proxies and audio is way low. turn off one channel- instant audio fix, levels are where they are supposed to be. I checked all inputs of camera- as i said all behave the same way- I have tested the two audio cables I have that go to mini xlr and they aren't reversed (I could check again I guess...)
I reloaded build 17 just in case that was it. No joy. Is there a fix i can do? Wait until new audio board comes in? anything else? try someone else's audio cables is next on my list.

 

[Nate Clapp]

AH HA! more extensive testing= camera good, cables bad. My two xlr>minixlr cables bought from red (at different times) are phase reversed after all! Whew! Sort of. now Ive got to fix...

 

[David Rasberry]

Standard pinout for audio XLR's is pin 1 shield, pin 2 hot, pin 3 cold. The pins numbers are molded on the connectors, though they may be hard to see. The most common wiring error is pin 1-pin 2 reversed as these are on opposite sides on male and female connectors. Pin 3 is the one in the middle. Phase reversal is Pin 2-Pin 3 reversed at one end of a cable

 

[Nate Clapp]

Thanks for that. I am printing that right now. Checking continuity was difficult due to the resistors in the old audio board friendly cables. had to open them up and check past resistors. in fact resistor soldering looks a bit daunting- connected in all sorts of ways across pins. I haven't sat down and studied it yet, but looks like a pain in the ass to fix. Good thing next few days are MOS (again)

 

[ibirds4]

You can reverse the phase on one of the channels anywhere in the audio chain to fix the problem on location. Most ENG mixers have a channel input that allows you to reverse phase as well as some wireless receivers. You can also buy a phase reversal barrel for about 30 dollars.

For more info on phase cancellation see the constructive and destructive interference article on wikipedia

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