Does waveform-based ASR with lowpass filtering preprocessing still require the assumption of FFT? I read some recent papers about time-domain speech recognition, and wondering if it steers away from the stationary assumption of FFT. However, some preprocessing operations like pre-emphasis and low-pass filtering still employ FFT. Does it mean waveform-based ASR with these preprocessing still has the FFT assumption of stationarity?

Many thanks!
Pre-emphasis and low-pass filtering can be done completely in the time domain (using IIR or FIR filtering, for instance), thus without an FFT (or with, by fast convolutions filtering methods).