A bitstream scalable audio coder using a hybrid WLPC-wavelet representation

In this paper, we present a novel bitstream scalable audio coder. In the proposed coder, the full bandwidth of input audio is first split into two. A hybrid WLPC-wavelet representation is used to encode the low frequency components (<11 kHz). In this method, the excitation to the WLPC synthesis filter is decomposed into subbands using a wavelet filterbank, and perceptually encoded. Two stage quantisation of the wavelet coefficients is used to provide scalability. The high frequency components of the input are assumed to be noisy, and efficiently encoded using an LPC noise model. The output bitstream is capable of being decoded at rates between 16 kbit/s and 80 kbit/s. As the bitrate increases, so too does the signal quality. At 80 kbit/s, the quality is near transparent. At the intermediate rates, the coder gives comparable performance to the MPEG layer III coder, when the MPEG coder operates at similar, but fixed, bitrates.