I don't think that's taking into account the harmonic frequencies. The 50Hz buzz is not a sine wave. That means that even with that filter, both 50 Hz mains sou

I don't think that's taking into account the harmonic frequencies. The 50Hz buzz is not a sine wave. That means that even with that filter, both 50 Hz mains sounds should still be detectable in the recording. Unless I'm missing something?