Active noise cancelling works by listening to the sound around you and playing its opposite, so the two cancel out before they reach your ears. It is best at steady, low noise: engines, air conditioning, the rumble of a train.

I wore a pair of over-ear noise-cancelling headphones on a daily commute for a month. On the train, the difference is striking. Switch them on and the carriage drops away; switch them off and you realise how loud it had been.

Voices and sudden noises still get through, which is a good thing on a platform. The sound itself is warm and clear, and at low volume, because there is nothing to drown out.

Two caveats. Over-ear cups get warm on a summer afternoon, and the large case takes up much of a small bag. But for a long daily journey, they are the most useful thing I carry.