Patent ID: 6353404
Filing Date: 2002-03-05
Classification: H03M

Abstract:
A D/A conversion apparatus comprising:a digital signal processor that carries out level conversion of input digital data by different conversion factors into a plurality of level-converted digital data, selects and outputs most appropriate data of the plurality of level-converted digital data based on a signal-to-noise ratio of each of said plurality of level-converted digital data, outputs other data of said plurality of level-converted digital data after attenuating the other data to or below a predetermined noise level, and switches between data previously selected as said most appropriate data and data newly selected as said most appropriate data by carrying out cross-fading between said previously selected data and said newly selected data; a plurality of D/A converters that carry out D/A conversion of said plurality of level-converted digital data output from said digital signal processor to respective analog signals and outputs said analog signals; and an analog adder device that carries out level conversion of said analog signals output from said plurality of D/A converters again based on respective corresponding ones of said conversion factors in a manner such that resulting analog signals have a level corresponding to a level of said input digital data, and then adds together all of the level-converted analog signals; wherein said digital signal processor carries out said switching over a predetermined cross-fading time period when an amplitude level of said input digital data crosses a predetermined threshold level from a larger side than said predetermined threshold level to a smaller side than said predetermined threshold level, insofar as the amplitude level of said input digital data does not cross said predetermined threshold level from said smaller side to said larger side for a predetermined hold time period, and said predetermined threshold level comprises a plurality of threshold levels, said predetermined hold time period and said predetermined cross-fading time period being set in a manner corresponding to each of said plurality of threshold levels such that as said predetermined threshold level is smaller, said predetermined hold time period and said predetermined cross-fading time period are set to respective shorter time periods.