speex回声消除算法

The echo canceller is based on the MDF algorithm described in: J. S. Soo, K. K. Pang Multidelay block frequency adaptive filter, IEEE Trans. Acoust. Speech Signal Process., Vol. ASSP-38, No. 2, February 1990. We use the Alternatively Updated MDF (AUMDF) variant. Robustness to double-talk is achieved using a variable learning rate as described in: Valin, J.-M., On Adjusting the Learning Rate in Frequency Domain Echo Cancellation With Double-Talk. IEEE Transactions on Audio, Speech and Language Processing, Vol. 15, No. 3, pp. 1030-1034, 2007. http://people.xiph.org/~jm/papers/valin_taslp2006.pdf There is no explicit double-talk detection, but a continuous variation in the learning rate based on residual echo, double-talk and background noise. About the fixed-point version: All the signals are represented with 16-bit words. The filter weights are represented with 32-bit words, but only the top 16 bits are used in most cases. The lower 16 bits are completely unreliable (due to the fact that the update is done only on the top bits), but help in the adaptation -- probably by removing a "threshold effect" due to quantization (rounding going to zero) when the gradient is small. Another kludge that seems to work good: when performing the weight update, we only move half the way toward the "goal" this seems to reduce the effect of quantization noise in the update phase. This can be seen as applying a gradient descent on a "soft constraint" instead of having a hard constraint.