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I've been mixing the multitrack Logic project files of a live performance. Overall audio quality is good, but there's a lot of bleed on the tracks. Bleed is expected in a situation like this, but it's worse than is usual due to the acoustics of the room. (I think this is mostly because of lots of high-acoustic reflections from a wall of windows behind the band. Other live recordings of the same band with much the same setup don't have these problems.)

A couple of the songs are good but the vocals need work. The performer in question was playing mandolin and singing, both captured by separate mics on stage. (He forgot his preamp that day so couldn't plug into the board.) Of course, the reverse will also be needed.

I'd like to fly in some vocal tracks from another live performance for the first few songs, where the singer was just warming up but the band was playing well, but I'll have to do a better job of isolating these tracks more so I have more freedom to edit. How can I reduce vocal bleed on an instrument mic and vice-versa?

The recording has additional problems, such as a lot of bleed into the drum mics (an overhead condensor and a dynamic mic for the cajon) but drums are more easily gated to deal with this. What strategies should I use to deal with this?

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2 Answers 2

Phase inversion may help.

Take a clean (no post-processing) mono vocal track and a clean mono instrument track. Invert the phase of one of them, and start playback. Listen closely while adjusting the relative playback positions of the tracks (offsetting a few samples at a time), to bring them closer to phase alignment. You may notice a slight improvement in isolation. Then bounce the pair of tracks to a single track, and use that bounced track in your final mix.

Of course, since in your recording the sound waves are scattered by acoustic reflections, there may not be any remaining perceptible phase coherence, so it might not help significantly, but it might be enough to give you some more options in post mixing. (I've successfully used this technique to improve isolation on a few muddy live recordings, anyway.)

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This is exactly the sort of technique I was hoping to elicit with this question. Thanks, and I'll try this one out. –  neilfein Feb 15 '13 at 18:51

Reduce stage noise is my #1 piece of advice. If using monitors, switch to in-ears. Often times a lot of the bleed actually comes from monitors as opposed to instruments or voices themselves. Also, using microphones with a more directional pickup can help to isolate the sound they pick up if it is a fixed source. Finally, if the sources in question fill different frequency ranges, it may be possible to use the EQ to reduce some of the cross over.

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This is good general advice, but the recording already exists and this isn't an option anymore. –  neilfein Feb 11 '13 at 18:33
    
@NeilFein - ah, sorry, I missed that it was specifically trying to clean up an existing recording, but I think that the input about the EQ is still valid. Really, that's all you can do. You are stuck with crap in/crap out. You can mute or reduce the volume of a channel if there isn't anything meaningful there, and if the frequency bands are different, then you can try to adjust the EQ to minimize issues, but what is on the channel is on the channel. There isn't any way to separate signals on the same channel once they are mixed if they are in the same frequency band. –  AJ Henderson Feb 11 '13 at 18:37

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