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Time-scale modification method and apparatus for digital signals

Image Number 8 for United States Patent #6801898.

According to a time-scale modification method or apparatus, wave segments each having a prescribed cutting length are sequentially cut from original digital signal waves stored in a waveform memory and are then spliced together by way of cross-fading, so it is possible to realize time-scale modification (i.e., compression or expansion with respect to time) in accordance with a designated time-scale modification factor. Herein, time-scale modification parameters such as a cross-fade duration, a search start time and a search end time are produced in response to the designated time-scale modification factor. In addition, a cutting start position is used for cutting a next wave segment following a present wave segment. The cutting start time is determined within a period of time between the search start time and search end time in such a way that it is placed to provide a best similarity between the wave segments having prescribed portions which are connected with each other by way of cross-fading. Specifically, a back-end portion of the present wave segment and a top portion of the next wave segment are smoothly connected together by way of the cross-fading, wherein they have the same cross-fade duration. The cross-fade duration is controlled to be longer as the time-scale modification factor becomes greater or smaller than "1". The cross-fading is actualized by a window function having different cross-fade coefficients, which are varied over a lapse of time and by which data of the prescribed portions of the wave segments are multiplied and mixed together.

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