0.4 Echo cancellation results

Results for the deconvolution method

Comparison of three methods of finding impulse response

Observations from magnitude of the frequency response

• The pseudo-dirac's frequency response is centered at higher frequencies that the magnitude of the responses given by the sine-sweep and the balloon pop.
• The sine-sweep has the most defined peak at low frequencies: lower frequency sounds tend to reverberate longer in closed spaces.
• The balloon pop has a sinc-like decaying envelope which could simply mean there is some noise involved.

Frequency response of acoustically desirable room

Comparing sine-sweep impulse responses

Compared to the acoustically desirable room, the OEDK classroom filtered out more high frequencies.

Results for the adaptive filtering method

For each of the three types of signals, an adaptive filter was trained with the recorded desirable signal (in Table 1 above). Then, for each algorithm, the filter was used to clean the echoed signal recorded in one of the two classrooms (echoic and OEDK). The resulting signals can be found below:

Rms values of the error signal

Since the purpose of the adaptive filter is to minimize the mean square error, the root mean square of the signal can be used to evaluate the effectiveness of each algorithm on the signals. Table 1 and Table 2 show the RMS values of the error signal when the corresponding algorithm has been used to train an adaptive filter with their corresponding desired signals (impulse to echoed impulse, male to echoed male, etc.)

Oedk male speech echo cancellation with lms algorithm

Oedk male speech echo cancellation with nlms algorithm

Oedk male speech echo cancellation with blms algorithm

Visually, it is apparent that the NLMS error signal's amplitude is smaller. This implies that the NLMS's output is closest to the desired signal.