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Audio missing from video depending how you view it

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Shawn Barry
Audio missing from video depending how you view it
on Mar 18, 2016 at 1:58:38 pm
Last Edited By Shawn Barry on Mar 18, 2016 at 2:49:13 pm

This is my first question to the Audio forum here, and this may not be an audio specific question, but I think it likely is. I'm having some REALLLLLLY strange results (I mean completely weird) with some recently rendered files.

Scenario: exporting video from Adobe Premiere and/or FCPX (same thing happens either way). Some video was recorded by an older Sony Handycam recording to digital tape. That audio gets mixed with music tracks often as well. So, I typically render out to 48000hz audio and either pro-res or h264 depending what has to be done with it. All the audio is exported to one track, along with the video.

Playback on desktop computer. All audio plays back fine.
Playback on TV (pay per view). Music is fine, camera audio is just a hiss (on same audio track)
Playback on iPhone - same as TV
This is where it gets really weird...
If I'm editing in Adobe Premiere CC, if I preview a clip with this configuration, the music plays back as well as the camera audio, but if I drop it into a sequence, the music is there, but the voice is missing.

I'm not exporting 2 audio tracks (unless I'm not but the application is without my option to change it, for some reason)

I'm not doing anything to the audio (no filters, no exotic settings)

When I render it all to one audio track, I would have assumed all the contained audio is rendered the same way, but that's obviously not the case. I'm a bit baffled. Has anyone experienced anything like this before?


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Richard Crowley
Re: Audio missing from video depending how you view it
on Mar 19, 2016 at 2:34:27 am
Last Edited By Richard Crowley on Mar 19, 2016 at 2:35:52 am

More likely than not, when the voice was recorded on your Sony handycam, it got recorded with the "right" channel in the OPPOSITE phase as the "left" channel. This is very commonly caused by using the wrong adapter between an XLR microphone and the 3.5mm stereo mic jack on the camera.

WHen you mix this down to monaural, the "left" track is CANCELLED by the opposite-phase "right" channel, and you get EXACTLY the symptoms you are describing.

To prevent this, use a properly wired adapter. For example: http://hosatech.com/product/xvm-100f/

To resolve your problem take the camera clips, separate the "left" and "right" audio tracks, and mute or delete the "right" track, leaving only the "left" track.

THe reason I am using "left" and "right" in quotes is because you really have only a single, monaural audio signal, but you have recorded OPPOSITE phases on the two stereo channels which are called "left" and "right".


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Shawn Barry
Re: Audio missing from video depending how you view it
on Mar 19, 2016 at 4:50:46 pm

Thanks for the run-down Richard. I'll go back through the footage again, and give that a shot.


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Peter Groom
Re: Audio missing from video depending how you view it
on Mar 19, 2016 at 6:02:44 pm

Richard will be right.
easiest solution is to take any audio that is disappearing, and drop off 1 side of the recording (fade down) and then pan the remaining centre and increase by 3 db. now it will be fine as you have removed the opportunity for phase cancellation.

Post Production Dubbing Mixer


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Shawn Barry
Re: Audio missing from video depending how you view it
on Mar 20, 2016 at 2:55:27 pm

Hmmm - after taking a dive in, I'm not sure what I'm looking for. I opened my audio tracks in Premiere's audio adjustment window and just see an audio track with L and R and both have equal data. If I adjust one or the other I hear the adjustments in my headphones, as I'd expect. So, I thought Premiere obviously doesn't have the audio chops to display the problem. I then opened the audio in Audition, and just see a more robust version of the same thing. An equal L and R audio. If I mute one, I just get audio in the other ear. So, basically I can't reveal the problem. Not being an audio engineer, I'm not sure what I'm looking for. Each time I open the audio, it looks like a normal audio track. If I mute a side, I get one-ear audio playback. That's obviously not what you're recommending, so I'm missing something.

Short of "teaching" me audio, is there any tip on what I should look for, or how I should be trying to view the problem in a way I can effect/correct it?


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Peter Groom
Re: Audio missing from video depending how you view it
on Mar 20, 2016 at 4:30:34 pm

yes you wont see any difference in the left audio and right. The problem is waaayy more subtle than that.
As I said, drop 1 side to off, pan the remaining side to center (hence only usinh 1 side of the stereo recording and your sorted.
Peter

Post Production Dubbing Mixer


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Shawn Barry
Re: Audio missing from video depending how you view it
on Mar 20, 2016 at 5:11:13 pm

Okay, understood. I thought I was looking for something other than normal in appearance.

Thanks for the help gentlemen.


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Richard Crowley
Re: Audio missing from video depending how you view it
on Mar 22, 2016 at 8:30:32 pm

You seem to be performing only the FIRST step of the process. You have two identical tracks, but one of them is OPPOSITE phase. As long as you listen to them in "stereo" it will be OK as your ears can handle it. But as soon as you MIX them down into monaural the "right" track will CANCEL the "left" track and give you exactly the symptoms you are describing.

First you GET RID of the "right" channel (by whatever method, depending on what software you are using). THEN you take the remaining "left" channel and put it into the center (for a stereo mix), or simply leave it as-is so that when you MIX everything down, you have eliminated that "right" channel that was cancelling your dialog.

Yes, when you listen in stereo, you are left with only dialog in your left ear. HOWEVER, if you mixed that down to monaural, everything will be in the CENTER. Or, if you need to maintain a stereo mix, then you simply take that audio track and PAN it into the center (or wherever you want it to appear.)


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