About reverberation and echo
If this distance is short, such as in a room or theater, the sound will be reflected back to the source in less than one-tenth of a second. This effect is reverberation. Because there is such a small delay in the sound repetition, sometimes only a few milliseconds, reverberation is often perceived by a listener as adding fullness to the original sound.
Reverberation will often be added to recorded music to better simulate the sound of a live performance, or to enhance the tone by making a thin sound fuller.