Question: I have a wav file that the subject is whispering in, how do I amplify without distortion? I have tried using Audacity, made it slightly better but audio still too low. 
Thanks

Answer: 
You actually need to increase the signal-to-noise ratio rather than simply "amplifying" the signal. To do this you need a noise reduction tool such as Izotope RX Spectral denoiser.
In audacity I'd normalize the audio, then look at the spectrum. Do an equalization, dropping the low frequencies significantly as well as the highs. A whisper is high frequency breathy, so keep trying different curves till you get the best sound. Also if there are non-speaking gaps you can use a gate to silence the noise between words. This can be disconcerting, but worth a try. 

[![equalization curve](https://i.stack.imgur.com/6ckkF.png)](https://i.stack.imgur.com/6ckkF.png)