TV station says I'm 'out of phase'.... at DVinfo.net

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Old October 31st, 2006, 11:03 PM   #1
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TV station says I'm 'out of phase'....

Alright here's the scoop. I do the shooting at a small local tv station. After I finish the shooting, The tapes get transferred downstairs where they get edited up and encoded into mpg2 where they get dumped onto a portable HDD and sent to the local transmitter station.

At any rate, here's the problem. I've gotten reports that 'some' viewers can't hear my programming. The president of our station visited the folks who do our transmitting and they're saying that the audio I'm recording is 'out of phase'. What should I be taking a look at to fix the problem?...or is it even a problem?

Here's my connection specifics:
Sony VX2100 w/ mic input set to 'mic' and NOT 'line'
Audio Technica ATX UHF connected with an XLR to 1/4" stereo mini-plug
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Old October 31st, 2006, 11:39 PM   #2
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Yep, something's screwed up all right.

I'm guessing that you're experiencing mono incompatibility, meaning, the viewers with stereo sets have no problem hearing your stuff, but those with mono are getting mostly silence.

Here's how it works - take a signal and split it, now you have two. Take one of those signals and reverse the wires. Now mix the two signals, you get a whole lot of nothing. Everything that was "plus" on the reversed signal is now "minus". Add it to the original signal and get zero.

To deal with this you need to figure out where in your workflow this is coming in. It could be right at the start, that xlr to miniplug. If so, you could see about rewiring the adaptor... cause it sounds like you don't edit your footage at all. If you did, you could just drop one channel of the audio in the edit.

Or, you could set your VX2100 to record to one channel only.

Or, you could tell whoever transfers your tapes to drop channel 2.

Possibly, this tv station has an engineer who does some bench work? Explain the problem, and he or she might fix up your adaptor in five minutes.

Used to be that broadcasters would always monitor for mono compatibility BEFORE the program hit the air...
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Old November 1st, 2006, 12:55 AM   #3
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The connection I'm using is a Hosa XLR to 1/8" (not the 1/4" I mentioned earlier...oops) and from what I've heard, they're pretty reliable. I might try using the receiver's 1/4" mini-out and see if that gives me anything different.

In the meantime, I have a whole slew of talent coming into the station to be recorded this week and won't have time to fix the problem on my end. Until I have time to look at things on my side, can I do something like splitting the signal so all I get is the left channel and mixing it down so I get the same channel coming out of both the right and left speakers instead of using a true stereo signal? This would mean a few extra steps for my post guys, but would keep me from having to rebook talent for a different day.

One last thing...is there a PC program I can pick up that would show me if something was out of phase to avoid this problem in the future?
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Old November 1st, 2006, 05:27 AM   #4
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Quote:
Originally Posted by Jeremy Rank
The connection I'm using is a Hosa XLR to 1/8" (not the 1/4" I mentioned earlier...oops) and from what I've heard, they're pretty reliable. I might try using the receiver's 1/4" mini-out and see if that gives me anything different.

In the meantime, I have a whole slew of talent coming into the station to be recorded this week and won't have time to fix the problem on my end. Until I have time to look at things on my side, can I do something like splitting the signal so all I get is the left channel and mixing it down so I get the same channel coming out of both the right and left speakers instead of using a true stereo signal? This would mean a few extra steps for my post guys, but would keep me from having to rebook talent for a different day.

One last thing...is there a PC program I can pick up that would show me if something was out of phase to avoid this problem in the future?
I'm thinking that the XLR to miniplug adapter might be the problem, not that it is defective but rather you simply have the wrong adapter for the task at hand. The mic receiver is putting out a mono, balanced, signal. A simple XLR to TRS adapter is intended to adapt a balanced XLR to a BALANCED MONO TRS, NOT an unbalanced stereo input such as is your camera's input jack when set to line input mode. They're wired XLR pin 2 (signal +) to mini TRS tip, XLR pin 3 (signal -) to TRS ring, and XLR pin 1 (signal ground) to TRS sleeve. Now a normal stereo connection has TRS tip going to the left and TRS ring going to the right. Using an adapter wired like this thus means you're sending signal + to the left channel and signal - to the right channel, you're recording the same mono signal on the left and right but 180 degrees out of phase with each other. You need to makeup or buy an adapter that puts XLR pin 2 to both TRS tip and TRS ring (jumper inside the TRS plug), XLR pin 1 to TRS sleeve, and XLR pin 3 either unconnected or jumpered to pin 1 (try both and go with the one that gives the cleanest signal). Id your present adaper is a short length of cable with the two connectors rather than a solid piece, simply go into the minplug end and unsolder the wire from the ring connector and and either leave it unconnected or solder it to the sleeve connector, then solder a jumper wire between the tip and ring connectors, Leave the wire going to the tip as is, of course. (And by the way, the Rode XLR-to-mini adapter is wired exactly this way, the proper way.) An even better way is a Beachtek or Sign Video XLR to mini adapter.

The most direct way to fix the footage you have is to load it into your NLE, seperate the stereo track into two mono tracks if necessary, select one of the audio tracks and simply invert its phase. Almost all NLEs will do that from the menu. Of course, if your tracks have already been mixed down with other material so they contain a mix of properly in-phase, say, music and other dialog along with your out-of-phase dialog, you're toast 'cause fixing your problem dialog will put the rest of the track out in the process.

This is why monitor control panels like the Presonus Central Station or Mackie Big Knob have a "mono" button on them and a lot of NLEs allow you to do the same in softwate. You should never release a stereo track from editing without giving it a listen all the way through collapsed to mono just to make sure you don't have these sort of rude surprises.
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Old November 1st, 2006, 07:31 AM   #5
 
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Actually, this is a fairly common problem. That's why it's ALWAYS recommended that you d a mono playback to check phase errors. There are several methods to visually/analytically check your phase, even without doing the standard mono playback test. Most good audio processors, for example Izotope Ozone, have a phase meter to check phasing. There is also a piece of freeware called VUMeter, that will let you visually check the phase on a "scope". Older recordings made on vinyl disks actually put sounds below 100 Hz intentionally out of phase because it used to cause the needle to physically jump out of the groove on a record.
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Old November 1st, 2006, 08:56 AM   #6
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TV station says I'm 'out of phase'

Why not just turn one channel off?? if youre recording a mono pair of channels fed by a single microphone, you only need one of them any way...if the problem is having the same exact program on both channels out of phase to each other and thus causing phase cancelation, just turn one channel off or down to zero, record a single mono channel, which in the NLE will simple be the "center" channel, or mono....BTW, (yeah fix it in post) some NLE's will allow you to reverse phase of an audio track ......
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Old November 1st, 2006, 08:59 AM   #7
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TV station says I'm 'out of phase'

Why not just turn one channel off?? if youre recording a mono pair of channels fed by a single microphone, you only need one of them any way...if the problem is having the same exact program on both channels out of phase to each other and thus causing phase cancelation, just turn one channel off or down to zero, record a single mono channel, which in the NLE will simple be the "center" channel, or mono....BTW, (yeah fix it in post) some NLE's will allow you to reverse phase of an audio track ......you also might consider picking up a Beachtek or Sign XLR adaper, and take the "funky" out of your gear setup....asl leaste part of the way.....
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Old November 1st, 2006, 09:28 AM   #8
 
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if the audio is fading in and out, then it's not a mono signal. unless it's a mono signal that's shifting phase as it plays back, which is a more serious problem than reversed connection polarity. another quick check would be to convert the L/R channels to Mid/Side. The Mid channel is equivalent to a mono signal, while the Side channel is the stereo info. If the Side channel is temporally zero, it's a mono recording.
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Old November 8th, 2006, 12:32 AM   #9
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I'd suggest inverting one channel to get the effect of noise cancellation.
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Old November 8th, 2006, 02:13 AM   #10
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Figured out it's not me...

I did a rundown of all my equipment. The Audio Technica is a mono output and runs through the Hosa XLR to mini connector into the VX2100. Hosa says that their connections are set up to use only a mono signal and then duplicate it so that you won't get a phase cancellation. This should hold true since I've done nearly twenty retail dvd's without so much as touching the audio on the shows and haven't had any problems.

Our station has a couple editors, one is using a VTR to transfer the footage and the other is using a cheapo-depot JVC camcorder to transfer the footage. Oddly, everything coming from the JVC transfers are causing the problems, so I'm thinking that the other camcorder is goofing up the audio somehow...

I tried to show the editors how to break down the signal into only a mono and then pan it over....only takes a couple seconds, right? They soundly snubbed their nose up at the idea saying that they already have too much to do to spend the extra five seconds to fix the audio. ugh...
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Old November 8th, 2006, 08:32 PM   #11
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I would look at the cable THEY are using from the JVC, I would bet that they are taking your signal, and then just using a simple cable that is causing the phase problems when they do the transfer.

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Old November 13th, 2006, 12:42 AM   #12
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me too!

i have the same "out of phase" problem my first tv production (only 5 minutes) has been rejected for this reason i have read all the previous replies and taken on board the great advice offered as i'm only a novice when it come to sound. the camera i used was an xm2 (gl2) with ma-300 xlr connector and a good mic, voiceover using sony uwpc1 wireless mic, sound track mp3 music all mixed to -10db.editing with premier pro. i do not have a dv deck so i use a canon mv700i. now the thing i can't work out is that when exported to dvd it sounds great (tested on a very expensive state of the art home theatre system) i even exported the production to tape then re imported to premier and exported to dvd again. no problem. the tv station sent me a dvd of what they uploaded from what i sent them and it sounded really tinny in places.i then sent another tape and was informed that the problem was still there. if i was at fault here wouldn't i be getting the "tinny sound as well ?
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Old November 13th, 2006, 07:57 AM   #13
 
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it really depends on what kind of system you have and what kind of system they have.
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Old November 13th, 2006, 08:02 AM   #14
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Quote:
Originally Posted by Craig Halstead
i have the same "out of phase" problem my first tv production (only 5 minutes) has been rejected for this reason ... if i was at fault here wouldn't i be getting the "tinny sound as well ?
Not necessarily. When you listen to in stereo, as you would be on your home theatre system or editing monitors, and definitely when you listen on headphones, it may sound just fine or you might not notice the effects of the phasing issues. But when the channels are phase reversed, a signal that appears on both left and right channels will have its waveform going positive in one channel while it's going negative in the other. When you mix the two together to get a mono signal, the positives and negatives will cancel each other out. If the signal is of equal strength in both channels, it will disappear completely from the summed mono mix. If it's unequal, some portion will remain but changed considerably in level. Because sounds are a complex waveform all sorts of strange things can result when they're mixed. This mixing can and does occur at many places along the broadcast chain anywhere from the broadcast studio to the TV sets of the audience. You can even hear it when listening in stereo when the mixing occurs in the air between the speakers and the listener and that's why speaker phasing is an important part of home theatre setups. The general term for the effect is comb filtering because different frequncies may selectively cancel or be reinforced. If you're watching broadcast TV in stereo and notice the sound suddenly ceases to be well localized and instead seems very diffuse, coming from everywhere all at once, that's a phasing problem in action (it tends to happen more often in locally produced commercials than in national spots or the program itself).

This, BTW, is why monitor control panels like Mackie's Big Knob or Presonus Central Station have mono buttons on them - to make it convenient for you to mixdown L&R stereo to mono as a check for problems before releasing the mix from editing.

Hope this helps
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