-
The magnitude or loudness of the echo is high.
-
The delay time between when you speak and when you hear your
voice reflected is significant.
-
The listener hears the speaker twice.
The two components of echo are loudness and delay. Reducing
either component reduces overall echo. When a user experiences delay, the
conversation can get choppy, and the words of the participants sometimes
overlap.
Note
Echo tolerance varies. For most users, however, echo delay over
50 ms is problematic.
There are two ways to solve an echo problem in your telephone
network:
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Echo suppression
-
Echo cancellation
The echo
suppressor, as depicted in Figure 2-22,
works by transmitting speech in the forward direction and prohibiting audio in
the return direction. The echo suppressor essentially breaks the return
transmission path. This solution works sufficiently for voice transmission.
However, for full-duplex modem connections, the action of the echo suppressor
prevents communication. Therefore, when modems handshake, the answering modem
returns a 2025 Hz tone to the calling modem, which serves to disable the echo
suppressors along the transmission path.
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