多媒体技术chapter-13-Basic-Audio-Compression-Techniques

2020/2/181Chapter13BasicAudioCompressionTechniques13.1ADPCMinSpeechCoding13.2G.726ADPCM13.3Vocoders13.4FurtherExplorationChapter132020/2/18213.1ADPCMinSpeechCodingADPCMformstheheartoftheITU'sspeechcompressionstandardsG.721,G.723,G.726,andG.727.Thedifferencebetweenthesestandardsinvolvesthebit-rate(from3to5bitspersample)andsomealgorithmdetails.Thedefaultinputisμ-lawcodedPCM16-bitsamples.Chapter132020/2/183Chapter132020/2/18413.2G.726ADPCMITUG.726supersedesITUstandardsG.721andG.723.Rationale(基本原理):worksbyadaptingafixedquantizerinasimpleway.Thedifferentsizesofcodewordsusedamounttobit-ratesof16kbps,24kbps,32kbps,or40kbps,at8kHzsamplingrate.Chapter132020/2/185Chapter132020/2/186Chapter132020/2/187Theinputvalueisaratioofadifferencewiththefactor.Bychanging,thequantizercanadapttochangeintherangeofthedifferencesignal-----abackwardadaptivequantizer.Chapter132020/2/188BackwardAdaptiveQuantizerChapter132020/2/18913.2G.726ADPCMChapter132020/2/1810Chapter132020/2/1811Chapter132020/2/1812Chapter132020/2/1813Chapter132020/2/1814Chapter132020/2/1815Chapter132020/2/1816Chapter132020/2/1817Chapter132020/2/1818Chapter132020/2/1819Chapter132020/2/1820