ref: 6bae11ebb8908f2836f82b52c2b3b117ffaa5191
dir: /src/highp.c/
/* * Sound Tools High-Pass effect file. * * (C) 2000 Chris Bagwell <cbagwell@sprynet.com> * See License file for further copyright information. * * Algorithm: Recursive single pole high-pass filter * * Reference: The Scientist and Engineer's Guide to Digital Processing * * output[N] = A0 * input[N] + A1 * input[N-1] + B1 * output[N-1] * * X = exp(-2.0 * pi * Fc) * A0 = (1 + X) / 2 * A1 = -(1 + X) / 2 * B1 = X * Fc = cutoff freq / sample rate * * Mimics an RC high-pass filter: * * || C * ----||---------> * || | * < * > R * < * | * V * */ #include <math.h> #include "st_i.h" /* Private data for Highpass effect */ typedef struct highpstuff { float cutoff; double A0, A1, B1; double inm1, outm1; } *highp_t; /* * Process options */ int st_highp_getopts(eff_t effp, int n, char **argv) { highp_t highp = (highp_t) effp->priv; if ((n < 1) || !sscanf(argv[0], "%f", &highp->cutoff)) { st_fail("Usage: highp cutoff"); return (ST_EOF); } return (ST_SUCCESS); } /* * Prepare processing. */ int st_highp_start(eff_t effp) { highp_t highp = (highp_t) effp->priv; if (highp->cutoff > effp->ininfo.rate/2) { st_fail("Highpass: cutoff must be < sample rate / 2 (Nyquest rate)\n"); return (ST_EOF); } highp->B1 = exp((-2.0 * M_PI * (highp->cutoff / effp->ininfo.rate))); highp->A0 = (1 + highp->B1) / 2; highp->A1 = (-1 * (1 + highp->B1)) / 2; highp->inm1 = 0.0; highp->outm1 = 0.0; return (ST_SUCCESS); } /* * Processed signed long samples from ibuf to obuf. * Return number of samples processed. */ int st_highp_flow(eff_t effp, st_sample_t *ibuf, st_sample_t *obuf, st_size_t *isamp, st_size_t *osamp) { highp_t highp = (highp_t) effp->priv; int len, done; double d; st_sample_t l; len = ((*isamp > *osamp) ? *osamp : *isamp); for(done = 0; done < len; done++) { l = *ibuf++; d = highp->A0 * l + highp->A1 * highp->inm1 + highp->B1 * highp->outm1; if (d < -2147483647L) d = -2147483647L; else if (d > 2147483647L) d = 2147483647L; highp->inm1 = l; highp->outm1 = d; *obuf++ = d; } *isamp = len; *osamp = len; return (ST_SUCCESS); } /* * Do anything required when you stop reading samples. * Don't close input file! */ int st_highp_stop(eff_t effp) { /* nothing to do */ return (ST_SUCCESS); }