NEED HELP - post audio question

[bosindy]

I am editing a trailer for a documentary and I am mixing in some footage of a congressional hearing. After I placed the footage in the timeline, it sounded fine on the speakers I have hooked up to my computer. It sounded fine on my old ancient macbook pro. Didn't think much about it after that.

THE PROBLEM: I showed the trailer to someone on their new macbook pro and when the congressional testimony came on, it was hard to hear. The audio was now thin and tinny. I recently bought a new macbook pro and same thing. the audio sounds terrible on the new macbook pro. I looked at the pan and it was -1 so i tried to even that our to 0 and you could no longer hear the audio at all.

this is the video clip on youtube http://www.youtube.com/watch?v=6KQ3CPoFBvU. I downloaded it off a fair use site the government has set up. transcoded to H.264 in FCP7.

The film was accepted to IFP week in NY and I have to get the long trailer, which has quite a bit of this footage in it, to them Wednesday. I am concerned they will watch on a MacBook Pro and the music will overcome the audio.

Is there anything that can be done? a filter perhaps, a different transcoding or bit-rate?

[Jason Ramsey]

that clip on youtube sounded like it was only coming through my rear speakers, if that helps.

[bosindy]

Thanks Jason,

maybe that's the answer. I had been listening on 2 speakers, on my old macbook and externals and the new macbook pros have 4 speakers?

is there a way to mix it with a filter to get it to go to all the speakers?

[bosindy]

that does seem to be the problem, the clip's audio only plays in the back speakers. Why would it not distribute to all 4 evenly like the HVX audio does? I don't want to start playing with surround sound, is there a simple fix for this from anyone?

[Steve House]

Sounds like a phase inversion issue. When you placed the file into your timeline you put copies on the left and right channels. Somehow the phase of one channel, most likely the right channel, got inverted. When they are mixed on playback and the pan is in the centre they cancel each other out. Surround decoders use phase information to determine where the channels should go and when your video is played the phase inversion tell it the hearings clip is intended for the back channels. Re-edit your soundtrack, dropping the hearings clip in as a single mono track instead of a stereo track and pan it to the centre using your workstation's pan controls

[bosindy]

Thanks Steve, your post got me thinking and I think it has been solved. Here is what I did. The audio in the original clip has the issue so it wasn't the timeline causing it (if that is what you meant) what I did was in FCP went in to modify and unlinked stereo pair. The top channel was pan left, I deleted the bottom channel, and it worked in the front speakers. I then copied the top channel placing it dirrectly below it and panned that one right. It now works. Not sure why, but it does. maybe this is similar to your idea as well, either way, it was your post that helped so thanks.

ps. panning it center would cut the audio completely out.

[Alex H.]

The top channel was pan left, I deleted the bottom channel, and it worked in the front speakers. I then copied the top channel placing it dirrectly below it and panned that one right. It now works. Not sure why, but it does.

Why go to the trouble of duplicating the track? Deleting one of the tracks fixed the phase cancellation, but in FCP you need only to pan the remaining audio clip to the center. Duplicating it and panning it to the other side can technically fix the issue, and give you audio from both playback channels, but you're introducing a new potential phase issue if one of the audio clips happens to shift. When you hit a phase issue like that, just - as you did to start - deselect the stereo pair and delete one track... but then pan the remaining one to the center and your problem is solved.

[Noiz2]

I suspect that Alex hit it on the head with the Phase Issue. The way that Dolby ProLogic gets four tracks or more (surround) into two physical tracks is by putting tracks out of phase with each other in a very specific way. It's designed so that if you play it in stereo it will sound OK but if you play it through a ProLogic decoder you will get front AND surround. The (probably mono) original must have gotten out of phase just enough (probably because of the encoding) that ProLogic would see them as surround channels. So on your stereo set up all was fine but the new MBP "decoded" the track and sent your main audio to the surrounds. This is actually confirmed a bit by them getting very quiet when you panned both center. Surround channels are 180 degrees out of phase in a ProLogic stream so summing them would have canceled them out.

Alex is correct that the better way to have fixed it would be to just pan the one track center. But that also would have lowered your level so what you did is probably better at this point since your levels should be exactly where they were.

[bosindy]

thanks guys, I appreciate your input. Alex's idea worked as well and good to understand a little more about what was going on.


Best,
Jim

[tyreeford]

Sounds like you have a polarity reversal issue somewhere.

Oh, and check to see if you have any "sound enhancer" filters on.

iTunes has a "sound enhancer" plugin that wacked out a couple of tunes, making them sound like they were being played through a washing machine.

Regards,

Ty Ford