Fog horn sound effect

A held low note that drops to a grunt at the end. It is the sound most people picture when they hear the words, and the drop is the part that makes it unmistakable.

Flat, electric, and utterly even from start to finish. Reach for it when the scene is modern, because the mechanical grunt of a diaphone dates a location by about a century.

The same note with the top taken off it and a faint return behind. Distance is built into the colour here rather than the level, so it still sits properly against a picture.

The pattern a station actually keeps: sound, silence, sound. The gap is what tells an audience this is machinery on a timer rather than a person leaning on a horn.

A bronze bell struck by its own rocking, so the strikes never fall evenly. That unevenness reads as swell, which is why one buoy can imply an entire sea state.

A breathy wavering moan pushed by rising and falling swell. The strangest of the six, and the one that turns a coastal scene uneasy without any music doing the work.