When a sound is followed by another sound by a very short amount of time – under 2 ms for clicks, under 50 ms for most complex sounds – the listener hears them merged together as a single sound. Delays over 50-100 ms are heard as echoes, flams, or bad timing.
In my own experiments, I have found that even the two sounds may appear to “happen” at the same time, changing the timing relationship between them can change the timbre of the merged sound.
Similar:
Law of the First Wavefront, Haas Effect,