High-pass filtering pre-processing before computing audio features
I agree that a large-order (12 taps+) high-pass Butterworth filter will be sufficient. 

Why?  Well, Butterworth filters are commonly used in professional audio-editing applications to do filtering, because their frequency response is designed to be as flat as possible in the passband. This means that the filtered audio is of higher quality/fidelity, as there are less frequency "ripples" or "artifacts" in the passband than other comparable filter types (Chebyshev, elliptic). In other words, Butterworth has a more linear phase response in the pass-band.

The downside is that the Butterworth filter has a slower roll-off, and will require a higher-order to implement a particular stopband specification. But this shouldn't be an issue for you.



To answer your second question, this is why the above solution is preferable to using an FFT and zeroing out the bins: Why is it a bad idea to filter by zeroing out FFT bins?