Acoustic Echo Cancellation (AEC)
This demonstration illustrates the application of adaptive filters to acoustic echo
cancellation (AEC).
Author(s): Scott C. Douglas
Contents
Introduction
The Room Impulse Response
The Near-End Speech Signal
The Far-End Sp ee ch Signal
The Microphone Signal
The Frequency-Domain Adaptive Filter (FDAF)
Echo Return Loss Enhancement (ERLE)
Effects of Different Step Size Values
Echo Return Loss Enhancement Comparison
Introduction
Acoustic echo cancellation is important for audio teleconferencing when simul-
taneous communication (or full-duplex transmission) of speech is necessary. In
acoustic echo cancellation, a measured microphone signal d(n) contains two sig-
nals: - the near-end speech signal v(n) - the far-end echoed speech signal dhat(n)
The goal is to remove the far-end echoed speech signal from the microphone sig-
nal so that only the near-end speech signal is transmitted. This demo has some
sound clips, so you might want to adjust your computer’s volume now.
The Room Impulse Response
First, we describe the acoustics of the loudspeaker-to-microphone signal path
where the speakerphone is located. We can use a long finite impulse response
filter to describe these characteristics. The following sequence of commands
generates a random impulse response that is not unlike what a conference room
would exhibit assuming a system sampling rate of fs = 8000 Hz.
M = 4001;
fs = 8000;
[B,A] = cheby2(4,20,[0.1 0.7]);
Hd = dfilt.df2t([zeros(1,6) B],A);
hFVT = fvtool(Hd); % Analyze the filter
set(hFVT,
'
Color
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, [1 1 1])
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