y = x - xm1 + 0.995 * ym1; xm1 = x; ym1 = y;Here, x denotes the current input sample, and y denotes the current output sample. The variables xm1 and ym1 hold once-delayed input and output samples, respectively (and are typically initialized to zero). In this implementation, the pole is fixed at , which corresponds to an adaptation time-constant of approximately samples. A smaller value allows faster tracking of ``wandering dc levels'', but at the cost of greater low-frequency attenuation.
Perform the bilinear transform defined above and calculate the coefficients of a first-order digital low shelving filter. Find the pole and zero as a function of , , and . Set and verify that you get a gain of . Set and verify that you get a gain of 1 there.
Normalizing Two-Pole Filter Gain at Resonance
DC Blocker Frequency Response