Microphone array (beamforming) or sound intensity. But since those approaches typically require expensive hardware, the current approach is basically "we don't"

Microphone array (beamforming) or sound intensity. But since those approaches typically require expensive hardware, the current approach is basically "we don't" unless the frequency characteristics are clearly distinct and we can use traditional equalization processes. Machine learning has potential (and a lot of people have tried) but it's only as good at it's training.