Adaptive Filter and Filtering Method for Low Bit Rate Coding

摘要

An improved filtering method is disclosed having two filters for use in an enhancement filter in a mixed excitation linear prediction (MELP) speech coder or in a post-filter in a codebook excitation linear prediction (CELP) speech coder. The first filter (62);The gatneunde, where P is the predicted value, α and β are scaling factors, z is the inverse and sig-prob of unit delay operation used in transform representation of the transfer function is a signal probability estimate, the second filter has a transfer function 1-μz ^{- 1} , where mu is a scaling factor. sig-prob is a signal probability value based on a comparison between the power of the signals of the current frame and the long-term estimate of the noise power in the signal probability estimator 63. [ If the power of the signals is greater than + 30dB noise power, the sig-probe value is 1 and if the power is less than + 12dB of noise power, the sig-probe value is zero. Between these two conditions, sig-prob is (log gain-12dB-noise gain) / 18.