The Research Of Low Bitrate Audio Compression Based On Spectrum Extension Technology

The traditional audio encoder usually discards high frequency contents to reduce bit rates, which also reduces the quality of the reconstructed audio. Bandwidth extension technology which employs a certain algorithm, can improve the perceptual quality of audio obviously with no additional bits or only a little of bits. So bandwidth extension technology has become a research hotspot in audio processing field.Spectral Band Replication is one of the famous approaches in audio band extension. High band analysis is done in SBR encoder, which extracts the high band side information that is sent to the decoder. With the low band signal that is decoded from core decoder and the side information, high band can be reconstructed correctly. PlusV is another approach applied in VLSI, which has rather simpler scheme and achieves lower performance. Bandwidth extension also developed a"blind"approach in which no side information is extracted in encoder. All that developed approaches performance differently, and each has its own shortcome.This thesis puts forward an algorithm of bandwidth extension that has simplified parameters (called SPBE in this thesis). SPBE concentrates on the correlationship analysis between the high band and the low band of audio signal, while high band is divided into several subbands. High band parameters of the correlationship information and high band energy information are extracted at last, to determine the details of high band extension. With this approach, Transient signal detection module, in which energy based unpredictability measurement is employed, is introduced to analysis input signal, in order to provide high time-resolvability when transient happens. MDCT, which is implemented by FFT based fast algorithm, is applied to transform the signal from time...