Filter coefficient setting technique for variable filtering process and variable sampling frequency conversion

A filter coefficient setting device for a filter performing a filtering process on a time series of digital signals by convoluting filter coefficients into said digital signals, said filter coefficient setting device comprising:

• a coefficient memory which stores therein a given first series of the filter coefficients;
• and
• a filter coefficient interpolator which performs an interpolation process on said given first series of the filter coefficients, wherein contents of the interpolation process are varied in correspondence to a desired filter characteristic to be achieved, in such a manner that the interpolation process generates a second series of filter coefficients according to an impulse response characteristic that is obtained as a consequence of expanding or compressing, in a time-axis direction, an impulse response characteristic represented by said given first series of the filter coefficients,
• wherein said second series of the filter coefficients generated by said filter coefficient interpolator is supplied to said filter so that said filter is set to the desired filter characteristic.

A method of converting a sampling frequency of a time series of digital signals inputted at a first sampling frequency into a second sampling frequency, said method comprising the steps of:

• performing an interpolation process on a given first series of filter coefficients, wherein contents of the interpolation process are varied in correspondence to a ratio between said first and second sampling frequencies in such a manner that the interpolation process generates a second series of filter coefficients according to an impulse response characteristic that is obtained as a consequence of expanding or compressing, in a time-axis direction, an impulse response characteristic represented by said given first series of filter coefficients;
• performing a filtering process on the digital signals inputted at said first sampling frequency by convoluting said second series of filter coefficients into said digital signals;
• and
• converting the sampling frequency of said digital signals, having undergone the filtering process, into said second sampling frequency.

A sampling frequency converter device for converting a sampling frequency of a time series of digital signals inputted at a first sampling frequency to a second sampling frequency, said sampling frequency converter device comprising:

• a coefficient memory which stores therein a given first series of filter coefficients;
• and
• a filter coefficient interpolator which performs an interpolation process on said given first series of filter coefficients, wherein contents of the interpolation process are varied in correspondence to a ratio between said first and second sampling frequencies in such a manner that the interpolation process generates a second series of filter coefficients according to an impulse response characteristic that is obtained as a consequence of expanding or compressing, in a time-axis direction, an impulse response characteristic represented by said given first series of filter coefficients;
• a filter which performs a filtering process on the digital signals inputted at said first sampling frequency by convoluting said second series of filter coefficients into said digital signals;
• and
• a sampling frequency converting circuit which converts the sampling frequency of said digital signals, having undergone the filtering process, into said second sampling frequency.