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Problem with audio output/playback on TV/select computer speakers

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Rosa Jurjevics
Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 8:55:12 pm

Hello --

My team and I have been having the following problem and haven't been able to either find a solution here (or elsewhere) or fix it myself. While my audio mix plays just fine on my computer (both in Final Cut and when exported to various file formats), when I play it on a TV or a computer with external speakers, one track drops down so low I can barely hear it. We have tried numerous workarounds (listed below) with no results. Any help would be greatly appreciated!

INFO:
FCP v7.0.3
Compressor:
DV/DVCPRO-NTSC (We have to edit in a 640x480 workspace -- not our choice)
Audio settings:
48kHz
16-bit
Channel-grouped
Audio outputs:
Stereo monitoring (2 outputs)
Stereo
0db downmix

The audio tracks in FCP that dropped out were from a Canon HG20, which uses the MTS codec. After being captured in FCP, they have the following settings:
Apple ProRes 422 1920 x 1080
Linear PCM
16-bit little endian signed integer
48 hz stereo (L R)

In FCP, the audio is two non-paired tracks. Each track has the same audio in it so it looks like it is dual mono...

We have tried:
-Switching the pan in both tracks to either L or R
-Switching the pan in both tracks to 0
-Switching the pan in one track to L and one track to R
-Switching the audio output settings to 5.1 monitoring (and downmixing all outputs to stereo in the mixer)
-Exporting the failed audio tracks to AIFF and re-importing the AIFF to the sequence
-Exporting the AIFF version of the audio tracks, converting it to MP3 (not good for FCP, I know), and putting the MP3 in the timeline
-Switching the sequence presets to match both the footage and the sequence frame size as best as possible (Apple ProRes 422 HQ NTSC 48khz)

We did SOMETHING that worked but my notes are a mess so we're trying to retrace our steps. I will post the specs of the working file when we find it!

Thanks!


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Michael Gissing
Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 9:02:09 pm

The likely problem is you have audio that is dual mono with the phase wrong for some reason. When mixed to mono the level drops due to phase cancellation.

By playing back on a TV it may be summing to mono so cancelling. Find the track that is doing that, pan both L &R to center and it should also cancel in FCP. If so then just delete one of the two tracks.


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Rosa Jurjevics
Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 9:09:03 pm

Thank you for your quick reply!

A question for you: When you say "pan both L&R to center," do you mean on both tracks? When we've done that, we don't hear anything at all... But if we haven't tried deleting one of the tracks.

Off to try your suggestion. Will report back.

Also -- what would have caused this, do you think? Would it have been in the recording of the sound? Something in FCP?


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Michael Gissing
Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 9:22:25 pm

If it is a phase issue then check cables from the mixer to camera. Phase errors are usually caused by pin swaps in cables.


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Rosa Jurjevics
Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 9:23:29 pm

This totally worked! Deleted one of the tracks and panned to 0. What happened to make it get so out of whack? I've never seen anything like this in all my years on FCP.


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Mark Suszko
Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 10:15:38 pm

What was happening was two identical tracks where the peaks and waves canceled each other out because they were out of phase. You can visualize this with a pot of water if you wiggle your right and left index fingers at opposite ends of the vessel the exact same way. The little waves come towards each other and the peaks of one fill the troughs of the other, leaving a flat spot in he water surface.

If you slipped one of those two mono tracks in final cut forward or back by a frame or two, you'd get the expected echo, but you'd also get the loudness back, because you changed the phase between the peaks and troughs.


You can also visualize this with two sets of jump-ropes being rotated so one is up and the other is down. We want them spinning together in synch.

This is the principle behind those noise-canceling headphones, for example: a mic inside the headphone hears the outside sound and feeds back the same exact sound but just 180 degrees out of phase. Exterior noise drops very low.

It is also the principle used in your shotgun microphone: those ports along the sides are precisely pattered to create phase canceling from the sides and phase reinforcement from just dead ahead.



We sometimes get calls from clients who can't hear a DVd on their TV or computer and it always boils down to the way they wired up their speakers, feeding them identical mono audio signals exactly out of phase, mirror images of each other. Yank one of the two speaker wires out and bam, audio is full on.


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Rosa Jurjevics
Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 10:53:57 pm

WOW. That makes sense and I never thought of that. I probably never would have thought of it either. Thanks so much for the explanation! I really appreciate it. One more bit of quirky audio knowledge to add to the mental data bank.


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Michael Gissing
Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 11:52:54 pm

Pleasure Rosa. It is a weird one if you haven't come across it before.


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Rosa Jurjevics
UPDATE! Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 9:06:19 pm

What worked on the TV here was an MP3 of the entire sound mix (originally an AIFF). It sounds GREAT. Everything else has been a total bust.


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Dave LaRonde
Re: UPDATE! Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 9:15:12 pm

Um, mp3 is a delivery, end-user type of audio compression. Are you at that point in this project? If not, avoid mp3 like the plague.

Dave LaRonde
Former Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Rosa Jurjevics
Re: UPDATE! Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 9:21:46 pm

Oh, yes, very true. I used the MP3 as a diagnostic experiment to try and isolate where the problem was (if it was in the sequence settings or in the actual audio file). Call it desperation. I remember trying to use an MP3 in FCP years ago and having it skip like a scratched 45... Since then, I've only used them when they are the ONLY audio file available.


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Dave LaRonde
Re: UPDATE! Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 9:26:54 pm

[Rosa Jurjevics] ". I used the MP3 as a diagnostic experiment to try and isolate where the problem was... I've only used them when they are the ONLY audio file available."

Actually, if you have FCP, you have QT Pro, and with QT Pro you can transcode any mp3 to an aiff 48kHz/16 bit file, no problem.

Or use Compressor. MP3's are never the only audio file available.

Dave LaRonde
Former Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Rosa Jurjevics
Re: UPDATE! Re: Problem with audio output/playback on TV/select computer speakers
on Nov 21, 2012 at 10:56:32 pm

Also true. I guess I've avoided doing that because, in the the past, I've had bad luck encoding MP3s to any other file type. The resulting audio contained major crackling and hissing... Not to mention lossy sound in general. I bet I've got the wrong settings or something else is up.


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