Code excited linear prediction speech coding

摘要

A CELP speech coder encodes a speech signal. The coder comprises a prediction filter (218) generating a predicted speech signal in response to an excitation signal. A subtraction unit (216) generates an error signal indicative of a difference between the predicted speech signal and the speech signal and a perceptual weighting filter filters the error signal to generate a perceptually weighted error signal which is filtered in a shaping filter (234) to generate a shaped error signal. The shaping filter (234) modifies a level of the perceptually weighted error signal in a lower frequency interval relative to a higher frequency interval. A codebook search controller (220) selects an encode excitation signal in response to the shaped error signal and an encoded signal is generated which comprises an indication of the encoded excitation signal. The shaping of the perceptually weighted error signal allows easy and efficient adjustment of a trade-off between wideband and narrowband speech quality.