A masker can mask sounds occurring before it is switched on.

Evidence

The effect of post masking corresponds to a decay in the effect of the masker and is more or less expected. Premasking, however, represents an effect that is unforeseen because it appears during a time before the masker is switched on. This does not mean, of course, that our hearing system is able to listen into the future. Rather, the effect is understandable if one realizes that each sensation - including premasking - does not exist instantaneously, but requires a build-up time to be perceived. If we assume a quick build-up time for loud maskers and a slower build-up time for faint test sounds, then we can understand why premasking exists. The time during which premasking can be measured is relatively short and lasts only about 20 ms. Post masking, on the other hand, can last longer than 100 ms and ends after about a 200- ms delay. Therefore, post masking is the dominant non-simultaneous temporal masking effect. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 487

Categorization

• DEEPTHINKING: The build-up time asymmetry explanation of auditory backward masking is a genuinely elegant mechanistic account of a counterintuitive phenomenon.
• XREF: connects to: The precedence effect makes the listening room’s first reflections mask the recorded hall’s acoustics — David Howard, Jamie Angus, coustics and Psychoacoustics, 2267