7 plot_ echo

Purpose

Displays the adaptive filter impulse response and the signals of interest in evaluating the performance of an echo canceler.

Syntax

plot_echo(w, x, r)

Description

Although formal testing of echo cancelers is a complicated process, usually quick performance measures are necessary during the process of developing the echo canceler. The plot_echo() function provides this quick performance measures. plot_echo() takes as input the adaptive filter coefficient vector $w(n)$, the echo canceler's subtractor input, and the residual signal, and returns after rendering the graph window. The variables of plot_echo() are summarized below.

 
Input arguments:
   w  : The adaptive filter coefficient vector
   x  : The echo-contaminated input signal
   r  : The residual signal
   x and r can be either vectors or wave files

Example

Figure 9.6: The echo canceler graph window.

An example graph window generated using plot_echo() is shown in Fig. 9.6. The generated graph has three panels. The top panel shows the coefficients of the adaptive filter at the moment of calling plot_echo() which is the impulse response of the echo path. The middle panel shows the input and output signals of the echo canceler subtractor. For acoustic echo cancelers, those two signals are the near-end speech $S_{in}$ and residual signals $S_{out}$, respectively (see Fig. 2.15). For network echo cancelers those are the $S_{in}$ and $S_{out}$ signals in Fig. 2.14. The bottom panel shows the evolution of the echo return loss (ERL) introduced by the echo canceler. The ERL is calculated as the ratio between the mean square values of the input and output of the echo canceler subtractor signals in dB.