SPEECH CODING METHOD APPLYING NOISE REDUCTION BY MODIFYING THE CODEBOOK GAIN

摘要

The invention refers to a method for encoding an acoustic signal (y(n)) containing a speech component and a noise component by using an analysis through synthesis method, wherein for encoding the acoustic signal a synthesised signal is compared with the acoustic signal for a time interval, said synthesised signal being described by using a fixed codebook and an associated fixed gain, comprising the steps: Extracting an estimated fixed gain (gn) of the noise component from the acoustic signal (y(n)) for the time interval; Representing the noise component for the time interval by its fixed gain (gn); Estimating a signal to noise ratio of the speech component to the noise component for the time interval based on the signal to noise ratio of an earlier time interval and a ratio of the acoustic signal (y(n)) to the noise component in the time interval; Determining a modification factor (gammac) based on the estimate of the signal to noise ratio; Deriving an estimate of a fixed gain (gs(m)) of the speech component by modifying said fixed gain of the speech component with a modification factor (gammac).