Recent acquisition of some insanely expensive hearing aids aimed at helping me out in cacophonous restaurants has set me thinking about the extent that modern life allows us to filter our intake of noise. This is big business. As sirens wail and Marvel blockbusters and rock concerts crash through legal decibel levels, controlling sound levels has become an increasingly sophisticated operation, abetted by everything from silicone pastilles and the volume-control knob to the wireless earbud.