IMPROVED EXCITATION SIGNAL BANDWIDTH EXTENSION

摘要

An apparatus for generating a high band extension of a low band excitation signal ( e LB ) defined by parameters representing a CELP encoded audio signal includes the following elements: upsamplers (20) configured to upsample a low band fixed codebook vector (u FCB ) and a low band adaptive codebook vector (u ACB ) to a predetermined sampling frequency. A frequency shift estimator (22) configured to determine a modulation frequency (O) from an estimated measure representing a fundamental frequency (F o ) of the audio signal. A modulator (24) configured to modulate the upsampled low band adaptive codebook vector (u ACB ? ) with the determined modulation frequency to form a frequency shifted adaptive codebook vector. A compression factor estimator (28) configured to estimate a compression factor. A compressor (34) configured to attenuate the frequency shifted adaptive codebook vector and the upsampled fixed codebook vector ( u FCB ? ) based on the estimated compression factor. A combiner (40) configured to form a high-pass filtered sum of the attenuated frequency shifted adaptive codebook vector and the attenuated upsampled fixed codebook vector.