Abstract
During the last decades, storage and transmission of high quality digital audio are becoming more and more important in, for example, digital audio broadcasting (DAB) and high definition television (HDTV). However, the required storage of high quality digital audio is usually massive. As for the compact disc signals (sampling rate of 44.1 kHz and 16 bits/sample), the bitrate requirement is 44100 * 16 =705.6 kb/s per channel and 1.41 Mb/s for stereo audio, which is too high for most applications. Thus we must develop techniques to reduce the bitrate requirement. In this thesis, the perceptual audio coder is reviewed and a coder based on wavelet packet transform is proposed. The distinct points about the proposed coder include: (1) it uses the wavelet packet transform rather than conventional Fourier transform or discrete cosine transform to exploit the capability of wavelet in, for example, treating nonstationary signals. (2) It tries to remove the redundancies between left and right channels in stereo audio to further increase the compression rate. Several wavelets are simulated and compared for audio compression in our experiments. From the experiments, the symmetric wavelet has the best effect for the coder. Different types of audio signals are also experimented in this study. An FFT based perceptual audio coder is also implemented for performance comparison.