Noise cancellation is designed to cut out the ambient noise - which is mostly white - of which there is a lot in a big city. It does this with a phase cancellat

Noise cancellation is designed to cut out the ambient noise - which is mostly white - of which there is a lot in a big city. It does this with a phase cancellation of what is probably a fairly predictable waveform. Human voices I can imagine are not that predictable. Maybe advances in machine learnings and processing may be able to provide better cancellation techniques.