[Speex-dev] questions concerning adaptation rate

[julia r.]

Hello Jean-Marc,
 
When you count the adaptation step size in case where the filter has already had
minimal adaptation, you use the following expression:
 
r = (0.7*r + 0.3*15*RER*e)/e*(power[i] + 10) = (0.7*leak_estimate*Yf[i] +
0.3*15*RER*(Rf[i] + 1))/((Rf[i] + 1)*(power[i] + 10)). 
 
Why do we need this weighted sum and the component 0.3*15*RER*(Rf[i] + 1)? Why
use the correlation-based RER if we can do the same in the frequency domain? If
we removed this component, the expression would be exactly like in the method
described in "On adjusting the learning rate in frequency domain echo
cancellation with double-talk". Or am I missing something?

Also, why do we use an increasing adaptation rate as the filter gets closer to
adaptation but isn't yet adapted? Wouldn't it make sense to decrease it?

Thank you,
Julia