| 摘要 |
A method of generating coefficients in a digital filter, comprises the steps of: <SL> <LI>(a) providing a gain control signal 6 setting a value of reference gain, <LI>(b) providing a frequency control signal 8 setting a value of reference frequency <LI>(c) calculating, according to a model of the frequency/gain characteristic of a prototype analogue filter, a plurality of gain and/or frequency points at frequencies equal to and less than Nyquist frequency (where Nyquist frequency is half the sampling frequency of the digital filter) and which match corresponding gain and/or frequency points in the corresponding digital filter characteristic, <LI>(d) calculating from the said calculated points, pre-warped parameters of a model of the analogue filter, <LI>(e) applying e.g. a bilinear a transform to the resulting pre-warped analogue model to convert the pre-warped analog model to the digital domain and <LI>(f) generating further coefficients from the transformed model and applying them to the filter. </SL> |
