| Summary: | 碩士 === 國立臺北科技大學 === 電腦通訊與控制研究所 === 90 === In this thesis, we study two tools in MPEG-4 general audio coding. The first tool is PNS (Perceptual Noise Substitution), which requires a noise detection mechanism. The detection method recommended by ISO uses the tonality index calculated in the psychoacoustic model. Though simple, the tonality index suffers from high sensitivity to small frequency variation and low discrimination power between defferent type of music. To cope with these problems, we adopt the detection approach proposed by Donald Schulz and compare the relative metris between these two methods in noise detection. In the noise substitution step, we propose to use the spectral values in lower frequency bands instead of random noise. The subjective experiments confirm that the proposed substitution approach has a better subjective quality for certain types of music.
The second tool studied is the block-switching mechanism. Since block switching increases the complexity of decoders as well as encoders, it is valuable if such a mechanism is replaced of other simpler approaches. We propose a method.
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