Research On Key Issues Of High Fidelity And Low Bitrate Audio Coding

Recent years various key technologies of high-quality and low bitrate audio coding have been developed, but the strong growth of digital audio business is in great need of high audio quality and low bitrate. By in contrast, audio compression and coding technology is a little far behind. So it is of great practical significance to do some research on these areas.A novel key technology of high fidelity and low bitrate audio coding, the technology of high-frequency band reconstruction based on the optimal choice of replication bands, is proposed in this thesis. Combining with the tonality and harmonic relationships and by using the correlation of high-frequency and low-frequency components, the proposed scheme is able to reconstruct the high-frequency components very similar to the original signals only with the low-frequency components and a few additional parameters reflecting the feathers of the high-frequency signals. Technically, it is an adaptive high-frequency reconstruction technique, so different audio signals with various characteristics can be processed by specific replication methods. Therefore three different replication strategies adapting to various audio characteristics and several algorithms for low bitrate audio coding are introduced, in which the high-frequency components are replicated by selecting the optimal matching low-frequency components according to the most relevant criteria. It reconstructs high frequency signals with high quality just by two steps, bands replication and envelope adjustment,.Comparing to the high-frequency reconstruction technology already available, the results of testing and analysis have shown that the technology proposed in this paper can reconstruct the high frequency harmonic more accurately and completely and the reconstructed audio sound great. Although in the current stage, there are still some shortcomings in this technology, it can be improved later by further studies.