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Carly Smith
broadcast audio out of phase?
on Apr 22, 2010 at 1:11:37 pm

Hi all -

We are editing shows for broadcast television and our most recent episode was sent back marked as "audio out of phase"

The station would not explain what this means or how to fix it - could someone please elaborate?

Suggestions on how to fix would also be helpful - please note that we are broadcasting shows built from archived live video that we may or may not have shot, so rerecording the audio is not an option.

TIA,

CS


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Mark Spano
Re: broadcast audio out of phase?
on Apr 22, 2010 at 3:40:02 pm

A normal stereo mix has some elements in the left and right channel that are common and elements that are different, creating the separation that makes stereo sound different from mono. Phase relationships between the channels can be slightly off, but not too far, otherwise it sounds weird and if you collapse the stereo mix into mono, elements will cancel out and disappear. This is probably what they are referring to - out of phase audio means that something in the left channel is 180˚ out of phase with the right channel and therefore will cancel out and be silent when summed together. Most likely you won't be able to change this if your audio came to you this way, but it may have something to do with the way you layed it to tape. If you are laying back analog, you'll need to check the wiring to make sure phase isn't being flipped somewhere down the chain. Do you have any scopes? A modern video scope like the Tektronix WFM7000 has a built-in audio metering section with a phase meter display. That would help as well. A quick and dirty way to check phase coherency is by exporting a section of your mix and bringing it into iTunes and installing the ancient TechRTA visualizer plugin for iTunes. This thing is old and buggy and you have to do a lot of clicking to get the phase scope up, but it can come in handy.



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Richard Crowley
Re: broadcast audio out of phase?
on Apr 22, 2010 at 3:47:40 pm

Is your sound track mono or stereo? Are you sending audio on both channels? What happens when you combine (sum, mix) the two channels together? If the audio is out of phase between the two channels they will cancel each other and leave near silence.

Unless there is some really compelling reason to send stereo, I would mix and produce mono and put exactly the same (mono) track on both output channels. You can't go wrong with that whatever kind of screwy (or not) workflow they are using at the station.


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Bob Zelin
Re: broadcast audio out of phase?
on Apr 24, 2010 at 3:23:20 am

Hi Carly,
because you are not explaining anything about your system, there can be countless reasons why you are making out of phase recordings. I am going to make a guess here, since you provide no information about your system. This is the most common reason of out of phase recordings - again, this is just a guess, as there are countless reasons that this could be happening.

I bet you have an analog audio mixer, and you are recording your source material into your record device (edit system, etc) via this analog audio mixer. And I bet it's a Mackie, Behringer or some type of analog mixer that uses 1/4" TRS phone plugs as the connectors. I bet if you check these connectors, that one of them is pulled half way out (not plugged all the way in). When this happens on one channel (and the other channel is all the way in), you get OUT OF PHASE recordings.

If this is not the case, no one can help you unless you describe your system.

Bob Zelin




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Carly Smith
Re: broadcast audio out of phase?
on Apr 27, 2010 at 6:50:09 pm

Thanks to everyone for the suggestions. Bob hit it the closest - yes, we primarily use Mackie boards, but we are using all XLR in/out, not 1/4" TRS.

We also get inputs from the locations we record in, so that could be (and has been) just about anything. RCA, 1/4", Mini, and XLR.

I did find a solution in post: Adobe Audition 3 has a phase meter built in, so I ran all the audio through the meter, and it did identify which sections were out of phase.
Select the area, press Invert, Save and when you run it through again - back in phase.

So now the real question is: why did Adobe bundle the inferior Soundbooth instead of AA3?



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Bob Zelin
Re: broadcast audio out of phase?
on Apr 27, 2010 at 11:16:44 pm

one of your XLR cables is wired incorrectly (reversing the red and black wires on pin2 and pin 3 will create an out of phase condition). You should NEVER be using the XLR inputs for anything but MIC signals on the Mackie. You will get peak distortion. All line level signals should be from 1/4" TRS only.

Bob Zelin




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