... of voice compression techniques used depends on the functionality required and affects the quality of the output. Compression for both speech and data is done through the removal of redundancy. In the case of speech compression, further compression can be obtained by removing irrelevancy, which is the imperceptible reconstruction error or distortion to the voice signal. For medium rate speech coding, an analysis-synthesis method is normally used. This means the speech is represented by a set of compact parameters which are then coded. Prior to compression, the speech signal goes through an analysis stage which can either be closed-looped or open-looped. In a closed-looped analysis, the parameters are extracted and coded and further reduced by a difference between the original speech signal and the reproduced signal. Hence this is also called an analysis-by-synthesis approach In addition, many voice-coding software products focus on telephone- bandwidth (approximately 4-kHz) audio compression. You achieve compression by ...

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