Stereo vs. Ch 1 + Ch 2

H

hanguolaohu

Active member
Hi,

I’ve been having major issues with the differences between “Stereo” and “Ch 1 + Ch 2” in FCP HD. I basically filmed with a shotgun on Ch 1 and the on-camera mic with Ch 2, so the audio levels and clarity on Ch 1 are much better and that is what I will use in the cut. All my footage was captured with “Ch 1 and Ch 2” under clip settings. When I look under the audio column in the browser, my clips are listed as “A1 + A2”. My question is:

1. When I watch a video clip with “A1 + A2” audio in the viewer, why do the levels in the audio meter (right of timeline) rise together as if it was recorded in stereo? But the waveform of the 2 channels in the timeline appear different.
2. Vice-versa, “stereo” files play in that audio meter at different levels for Ch 1 and Ch 2, which seems to me to be the reverse of what should happen.
3. When I use that “A1 + A2” clip in other projects, sometimes it changes to “stereo”. Why is that?
4. While capturing, does Final Cut Pro ever mix the Channels 1 & 2 into 2 channels of identical (mono) sound? I do NOT want that.

Am I the only one confused by this terminology? I’ve read the manual and Lisa Brenneis’ book about the differences. Should I just reverse my previously held view of what combined stereo and separate Ch 1 & 2 mean? This whole problem originated when I gave footage to my transcibers and they complained that the audio was not clear in many parts (yes, I know I used a shotgun). So while watching the footage I discovered that some parts had Ch 1 and 2 rising together, which led me to conclude that the audio was mixed together during capture. I’m hoping this did not happen as it will result in me having to recapture dozens of hours of footage.

Any help most appreciated,
Alexander
 
Open the audio mixer! In the tool menu. In general, separate channels are panned to center, so are indeed blended into mono output. Stereo channels by default are panned hard left and right. The stereo output of two channels panned center will look like two identical channels (a mono signal). That's why stereo files produce different left and right values, and summed mono files have identical left and right values.

You can disable one of the tracks on a clip-by-clip basis using the audio mixer with the mute button, or you can disable entire audio tracks in the timeline with the enable/disable buttons on the left.

Other projects may default to treating clips as stereo vs. 1+2 by default. But again, the audio mixer will make everything clear. When the playhead is inside a given clip, that clip's information will appear (and be controllable) in the audio mixer.

I don't think FCP ever blends channels on capture in the permanent way that you fear. As long as you actually captured the stuff to two different channels in the camera, you should be able to separate 'em in FCP. It's all about panning!
 
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Final Cut captures audio as either stereo "pairs", or separate A1 and A2, depending on your capture settings. The audio tracks are not "blended" together. Stereo pairs are simply two audio tracks that are "locked" together during editing (so any edit will be performed to both tracks) and the separate A1 and A2 tracks are not "locked" together (edits can be performed separately). Stereo pairs can be unlocked at any time and handled like independent audio tracks (A1,A2).
 
I'm giving my transcribers only the quicktime files to listen to. So is it safe to assume that in their headphones the left side will be Ch. 1 and the right side Ch. 2 of my camera footage? My concern was that I would have to redigitize my footage to get separate channels of sound, but according to what you guys have said the difference between "stereo" and "Ch 1 + Ch 2" is just a panning function within FCP. Correct?

Thanks,
Alexander
 
Um... maybe not! If you are exporting quicktime from FCP, and choosing stereo output rather than multiple mono (ch1 + ch2), then indeed FCP will mix them down according to the panning in the audio mixer. If you have them panned center, and output a stereo mix, you'll get a mono signal. So, make sure you either output as separate channels, or pan them the way you want before outputting as stereo.
 
it sounds like you've got both channels panned to the center. so ch 1 and ch 2 are both coming out of left and right in equal proportions. this is how a1 and a2 channels will open by default. (basically all this has been said before, with sligh semantic differences.)

from the setup you describe, you don't want 1 panned left and 2 panned right. this would give you (mostly) better sound in one ear/speaker, and the mostly bad sound in the other.

based on your setup, you probably want to lower the level of a2, since this is the inferior (on-cam) sound. you might even want to eliminate it altogether. if you need it for certain parts, bring it up when you need ambience, or the shotgun wasn't pointed in the right way or whatever.

this is less of a panning issue than a mixing issue. (yes, panning is part of mixing, but i'm talking about volume levels.)

if the shotgun (a1) has your main dialogue, you'll generally want to keep it panned pretty much middle.
 
I've encountered the same situation many times. What I usually do, as mentioned above, is unlink the tracks then delete the offending audio track (a2), copy the good track (a1) and paste it. Then realign the pasted track with the original track and make them a stereo pair. Making them a stereo pair pans one to the left and one to the right, instead of stereo pair you could just link them back together and pan them however you want.
 
A less permanet method is to use the pan control on the individual clip. on the bottom of each channel there is a dark blue line. Pulling that line up toward the middle will pan your audio so you could eliminate the sound from one channel by spreading the sound from the other channel over it. But reversing the process is just as easy.
 
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