4.3.3 Double-Talk Threshold

The full-duplexity of the AEC means the level of how much the far-end user can listen to the near-end user voice, while both users speak simultaneously. In general, this parameter maps to a threshold that controls the AES to suppress the echo non-linearly. If this parameter is configured to be more favorable for half-duplexity, the double-talk capability gets degraded more but removes more residual echo.

If assuming that x[n] is near-end signal and y[n] is far-end signal, the cross-correlation equation between these signals is indicated as follows:

Echo_corr = EMA (corr_coef), where EMA is the exponentially moving average.

Equation 4-1. Cross-Correlation Equation

c o r r_c o e f = Σ x [n] y [n] \div (\sqrt{Σ x {[n]}^{2}} \sqrt{Σ y [{n]}^{2}})

If selecting the Double-Talk Threshold as 0x50, the threshold to determine the presence of echo is also high. As a result, the AES function is less likely to get enabled to suppress residual echo. The following figure illustrates the Double-Talk Threshold parameter.

If selecting the Double-Talk Threshold as 0x2D, this setting is more active to enable the AES function for echo suppression.

Figure 4-4. Double-Talk Threshold Parameter