So am I right in thinking the first 'filename' is left channel/stereo and the 2nd 'filename' is right channel?
No, but holy shit you seem to have stumbled on how to isolate a single channel of a multichannel file. So, thanks for that!
Well, you're sort of right, but they're not filenames; they're array names. What I was trying to say with my earlier example (and sorry for not being clear, I was rushing a bit) is that you would have two arrays, in this case named "rightarray" and "leftarray". These two arrays would hold the right and left channel of a stereo file "foo.wav", respectively.
Now, when [soundfiler] loads a multichannel file, it puts each channel in a different array depending on the number of array names you give it. If you only give it one, it loads the first channel of the file. If you give it two, it loads the first two, etc. With stereo files, the first channel is the left one and the second is the right one. So if you only give it one array, it will only load the left channel. In order to load the right channel, you have to give it a second array name. But, it seems that if you make both array names the same, it will load the left channel into the array, and then overwrite that with the right channel. Brilliant!