| 摘要 |
An improved VQ system for compressing a digital signal produces a compressed signal by dividing the signal to be compressed into a series of signal segments. Each signal segment comprises a plurality of signal values. The improved VQ system uses first and second tables of vector values having different degrees of signal correlation, referred to as a class-1 table and a class-2 table respectively. For a selected signal segment, the VQ system determines a vector Xbar1 representing a difference between the signal values in the selected segment and an average of a selected group of signal values in a preceding segment. For the same signal segment, the method and apparatus determines another vector Xbar2 representing a difference between the signal values in the selected signal segment and an average of a selected group of signal values in the selected signal segment. The vectors Xbar1 and Xbar2 measure different levels of correlation between the signal values of the selected signal segment. The improved VQ system finds an entry in the class-1 table that is a best match for the vector Xbar1, referred to as a class-1 best match entry. The improved VQ system also finds an entry in the class-2 table that is a best match for the vector Xbar2, referred to as a class-2 best match entry. After determining the best match entries, the improved VQ system inserts into a compressed signal stream an identifying code or compressed signal representing a selected one of the class-1 best match entry or the class-2 best match entry.
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