This may have been covered elsewhere in the forum, but I just found something out using ReaFir to remove a subtle background noise (e.g. the hiss/shhhhhh we get from recording with a condenser mic).
The tip is this:
Don't Automatically Build the Noise Profile (i.e. using a small place where you have silence) before you have added the FXs, but
after! And then set ReaFir as the last FX in your chain.
I swear, I just spend the last hour trying to get rid of a small minuscule artifact that occurs when you Automatically Build the Noise Profile before putting FXs and up top, first in the FX chain. The artifact can be heard when the instruments stop playing and the WAV file goes towards silence. What you hear is sort of like the sound 'skipping'; you got some low level instrument sound coming through in small random spikes along with the hiss/shhhhh and with pure silence all mixed together coming through (if you listen really hard with headphones).
But when you Automatically Build the Noise Profile
after the FX (i.e. while playing the song with the virtual amp, eq, compression, delay, etc., using that same little bit of silence in the song) it gets almost 90% rid of that artifact. It is still a bit there, but can be tamed by lowering the WET envelop of ReaFir (i.e. telling ReaFir to process more gently the signal).
The artifact is probably due to fact the other FXs in the chain(e.g. especially the compression I suspect?) are boosting the small leftovers of whatever ReaFir is letting through. This does not happen when ReaFir is at the end of the chain processing the end signal.
Pretty simple hun?
Anyway, I hope this helps someone else to deal more efficiently with the backgroud hiss/shhhhh noise using ReaFir.