|
|
|
Not surprisingly, the louder the echo, the more distracting it is. Echo cancellation in effect consists of attenuating the amplitude of the echo part of the signal so that the echo is not easily heard. As some point, the echo becomes so quiet that it disappears, as compared to the foreground volume of the call.
Volume is typically measured in decibels (dB). You have probably seen the charts that show that a whisper is in the range of 20 dB while a jet engine or a rock band is around 120 dB.
Echo strength, which is equivalent to volume, is measured as echo return loss (ERL). The ERL sets some boundaries on the ECAN’s function because the echo must be weak enough to be distinguished from regular speech. In practice, this means that echo must be 6 dB quieter than the speech it appears alongside for the ECAN to be able to suppress it. If the echo is louder than this, it typically falls into the volume range of the actual replying speaker and cannot be safely removed without endangering the conversation contents. So, if an echo were actually present in a telephone conversation and so loud that the ECAN could not distinguish it from the conversation, you would be more or less doomed to a very bad call with high levels of echo.
| Copyright © 2012 CA. All rights reserved. |
|