Blind equalization for robust telephone based speech recognition

An adaptive filter in a blind equalization scheme has recently been proposed in order to reduce telephone line effects for speech recognizers. This paper presents the principles of this filter and describes the implementation of a circular-convolution frequency domain adaptive filter in the blind equalization scheme. The property of a constant long-term speech spectrum helps to compute the gradient used for the adaptation of the weights. However, using this property in a straightforward manner results in a crude implementation of this filter. Alternative computations of the standard stochastic gradient algorithm are therefore evaluated. On the basis of the speech recognition results obtained from different speaker independent telephone databases, this filter proves to be efficient for the channel equalization task.