Patent ID: 6362764
Filing Date: 2002-03-26
Classification: H03M

Abstract:
A D/A conversion apparatus comprising:a digital signal processor that carries out level conversion of same 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 quality 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 comprises: a cross-fading section that carries out cross-fading between said previously selected data and said newly selected data; a delay section that delays said input digital data by a predetermined amount of delay which is shorter than a time period required for completion of said cross-fading carried out at a predetermined cross-fading rate by said cross-fading section; and a cross-fading control section that controls said cross-fading section such that when an amplitude level of said input digital data exceeds a predetermined threshold value, said cross-fading section starts said cross-fading at said predetermined cross-fading rate between said previously selected data and said newly selected data which are delayed by said predetermined amount of delay by said delay section, and that when during said cross-fading a rate of change in said amplitude level of said input digital data, which is larger than a predetermined rate of change, is detected, said cross-fading section carries out said cross-fading at a cross-fading rate larger than said predetermined cross-fading rate in dependence on said rate of change in said amplitude level of said input digital data.