Defined in carb/audio/AudioTypes.h

constexpr int64_t carb::audio::kImperceptibleDelay = 200000

An estimate of the time in microseconds below which many users cannot perceive a synchronization issue between a sound and the visual it should be emitted from.

There are definitely some users that can tell there is a problem with audio/visual sync timing close to this value, but they may not be able to say which direction the sync issue goes (ie: audio first vs visual event first).