Yamaha Corporation

Ryuuji Wakatsuki

Kiyoto Kuroiwa

Koji Niimi

Tsugio Ito

Toshihiko Kawano

Measuring gate pulse is generated that rises in synchronism with one of first and second clock signals and falls in synchronism with the other of the first and second clock signals. Then, a pulse width of the generated measuring gate pulse is measured by counting clock pulses higher in frequency than the first and second clock signals. When counted values indicative of respective pulse widths of an adjacent pair of the measuring gate pulses generated in succession coincide with each other, it is determined that the frequencies of the first and second signal are the same, but when the counted values of the adjacent pair of the measuring gate pulses do not coincide with each other, it is determined that the frequencies of the first and second signal are not the same.

Clock-synchronism evaluating apparatus and method

Most appropriate data of a plurality of level-converted digital data obtained by level conversion of the same input digital data by different conversion factors is selected based on a signal quality of each level-converted digital data. The other level-converted digital data is attenuated to or below a predetermined noise level. Switching between previously selected data and newly selected data is effected by cross-fading. The level-converted digital data are D/A converted to respective analog signals. Level conversion of the analog signals are carried out again based on respective corresponding ones of the conversion factors to restore a level of the input digital data, and all the level-converted analog signals are then added together. When an amplitude level of the input digital data exceeds a predetermined value, the cross-fading is started between the previously selected data and the newly selected data which are delayed by the predetermined amount of delay, and when during the cross-fading a larger rate of change in the amplitude level of the input digital data than a predetermined value is detected, the cross-fading is carried out at a rate larger than a predetermined rate in dependence on the rate of change in the amplitude level. In another form, the cross-fading is started at a first rate when the amplitude level exceeds a first predetermined value, and when during the cross-fading the amplitude level exceeds a second predetermined value larger than the first one, the cross-fading is carried out at a second rate larger than the first rate.

Digital to analog conversion apparatus and method with cross-fading between new and old data

A D/A conversion apparatus includes a DSP which receives and converts input digital data with different conversion factors, to generate a plurality of digital data having different levels, selects one of the plurality of the generated digital data, depending upon the signal quality of the input digital data, while attenuating the other digital data to be lower than a predetermined noise level. A plurality of D/A converting devices convert the respective generated digital data into corresponding analog signals. A re-converting device converts the level of each of the analog signals into an original level, based on a corresponding one of the conversion factors with which the input digital data is converted by the DSP. An adding device adds the re-converted analog signals. An attenuating device attenuates, in an input stage of the adding device, medium-to-high frequency components of at least one of the analog signals generated by at least one of the D/A converting devices that receives the attenuated digital data, and corresponding to digital data obtained by converting the input digital data with a smaller conversion factor than that of the digital data selected and generated by the DSP.

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Hamamatsu, Japan

Ryuuji Wakatsuki