| Vehicle traveling data recorder only record the car's parts of running parameters, such as operating position, status, speed, latitude and longitude, time and other data. But in the passenger carrying vehicle's operation and management, record of car accidents and passengers'behavior is a blank. With the rapid development of computer technology and the digital technology, audio signal processing technology based on the embedded system would be applied to long-distance bus operation and management, a new type of vehicle traveling data recorder would come into being. Limited by the amount of storage of solid storage medium, a research for audio compression technology base on vehicle traveling data recorder is imperative. Ogg/Vorbis can provide high quality audio compression with advanced perceptual coding and transform coding technologies and because of its completely open and non-patent, meet the requirements of vehicle traveling data recorder.Researching for the Ogg/Vorbis audio compression technology, a novel efficient algorithm for the computation of modified discrete cosine transform is proposed. And then, a design of Ogg/Vorbis codec is achieved and Ogg/Vorbis audio technical compression properties are tested.Firstly, the paper introduces the background and significance of the subject, analyses encoding and decoding processes of Ogg/Vorbis audio compression technology, applies the focus of study and research programs by calculating the intensity experiment.Secondly, an efficient and fast algorithm for computation of MDCT/IMDCT is focused on. The recursive algorithm is analyzed. Because of the disadvantage of recursive algorithm, high complexity and error cumulative, an efficient and fast algorithm for computation of MDCT/IMDCT is proposed. The MDCT with block size N is converted into DCT -â…£and DCT-â…¡with block size N/2, and then a modified window is shown, which is piece-wise symmetric. The analysis of the proposed algorithm in terms of computational complexity is provided. The proposed algorithm achieves at last 20 %reduction of arithmetic operations compared to the traditional method.Last but not least, combined with project requirements and design principles, a design of Ogg/Vorbis codec is achieved, according to characteristics of vehicle audio signal, some modifications were made on source-code of library to improve the audio quality. Experimental results show that Ogg/Vorbis audio format has a higher compression ratio and better quality characteristics compare to Mp3 format. What's more, in the same bitrate Ogg/Vorbis audio format has an even higher cutoff frequency and better resolution, compression with 64kbps bitrate could meet the requirements of vehicle traveling data recorder. |
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