"I do interviews using Skype and record them with Audio Hijack Pro, using the left channel for input and right channel for output.
Is there another simple app like Fission that can do this? I want to be able to adjust the levels of the input and output individually."
I can't speak much for Audacity, haven't used it much.
As long as the left and right channels are recorded on a _single_ track (i.e., a "stereo" track), I'm guessing that you can't do much in the way of "editing" to manipulate the levels individually "within the same track".
In other words, if you want to adjust levels "individually", you're going to have to "break out" the left and right audio channels into _separate tracks_. Once done, you will easily be able to make such changes.
This is strictly "after the fact" processing, to be done after the tracks are recorded.
Here's how I would do it:
1. First, make a "dupe" of the original stereo track. You will end up with TWO stereo tracks, identical in content.
2. Then, use your DAW software to convert the first track, going from "left to stereo" or "left to mono". What you will end up with is only the "left channel content".
3. Next, convert the second (duped) track from "right to stereo" or "right to mono".
4. You will now have two tracks, one of the [original] "left", and the second of the [original] "right"
A DAW that can do this -- and do it easily and quickly -- is Cubase.
If you can get ahold of a copy of Cubase LE4, it will be all you need. "LE4" is a "bundled app" that comes with numerous audio interfaces sold. It's "free", a part of the package, but you can't buy it separately.
The full version of Cubase costs several hundred dollars and probably not worth the expense.
A good compromise is "Cubase Essentials", which can be found on ebay for $100 or less. "Essentials" is a "step up" from LE4, but not as "fully-equipped" as the "full version". It _will_ do what you need to do.
Not sure if Audacity can convert "left to stereo" or "right to stereo". Others who use it -- can it do this?