Echo is the sound signal after a series of reflection, I hear his speech sounds, this is the echo. Some echo is necessary, such as theater and music echo room echo delay time is short; and most echo will have a negative impact, such as duplicate hear your own voice when speaking of wired or wireless communication (recall those years we open when black playing the game, which if a man opened the loud speaker, his voice would resound resound to go). Thus eliminating the negative impact echo of the communication system is essential.
