#include "emu.h" #include "filter.h" static filter* filter_alloc(void) { filter* f = global_alloc(filter); return f; } void filter_free(filter* f) { global_free(f); } void filter_state_reset(filter* f, filter_state* s) { int i; s->prev_mac = 0; for(i=0;iorder;++i) { s->xprev[i] = 0; } } filter_state* filter_state_alloc(void) { int i; filter_state* s = global_alloc(filter_state); s->prev_mac = 0; for(i=0;ixprev[i] = 0; return s; } void filter_state_free(filter_state* s) { global_free(s); } /****************************************************************************/ /* FIR */ filter_real filter_compute(filter* f, filter_state* s) { unsigned order = f->order; unsigned midorder = f->order / 2; filter_real y = 0; unsigned i,j,k; /* i == [0] */ /* j == [-2*midorder] */ i = s->prev_mac; j = i + 1; if (j == order) j = 0; /* x */ for(k=0;kxcoeffs[midorder-k] * (s->xprev[i] + s->xprev[j]); ++j; if (j == order) j = 0; if (i == 0) i = order - 1; else --i; } y += f->xcoeffs[0] * s->xprev[i]; #ifdef FILTER_USE_INT return y >> FILTER_INT_FRACT; #else return y; #endif } filter* filter_lp_fir_alloc(double freq, int order) { filter* f = filter_alloc(); unsigned midorder = (order - 1) / 2; unsigned i; double gain; assert( order <= FILTER_ORDER_MAX ); assert( order % 2 == 1 ); assert( 0 < freq && freq <= 0.5 ); /* Compute the antitrasform of the perfect low pass filter */ gain = 2*freq; #ifdef FILTER_USE_INT f->xcoeffs[0] = gain * (1 << FILTER_INT_FRACT); #else f->xcoeffs[0] = gain; #endif for(i=1;i<=midorder;++i) { /* number of the sample starting from 0 to (order-1) included */ unsigned n = i + midorder; /* sample value */ double c = sin(2*M_PI*freq*i) / (M_PI*i); /* apply only one window or none */ /* double w = 2 - 2*n/(order-1); */ /* Bartlett (triangular) */ /* double w = 0.5 * (1 - cos(2*M_PI*n/(order-1))); */ /* Hanning */ double w = 0.54 - 0.46 * cos(2*M_PI*n/(order-1)); /* Hamming */ /* double w = 0.42 - 0.5 * cos(2*M_PI*n/(order-1)) + 0.08 * cos(4*M_PI*n/(order-1)); */ /* Blackman */ /* apply the window */ c *= w; /* update the gain */ gain += 2*c; /* insert the coeff */ #ifdef FILTER_USE_INT f->xcoeffs[i] = c * (1 << FILTER_INT_FRACT); #else f->xcoeffs[i] = c; #endif } /* adjust the gain to be exact 1.0 */ for(i=0;i<=midorder;++i) { #ifdef FILTER_USE_INT f->xcoeffs[i] /= gain; #else f->xcoeffs[i] = f->xcoeffs[i] * (double)(1 << FILTER_INT_FRAC) / gain; #endif } /* decrease the order if the last coeffs are 0 */ i = midorder; while (i > 0 && f->xcoeffs[i] == 0.0) --i; f->order = i * 2 + 1; return f; } void filter2_setup(device_t *device, int type, double fc, double d, double gain, filter2_context *filter2) { int sample_rate = device->machine().sample_rate(); double w; /* cutoff freq, in radians/sec */ double w_squared; double den; /* temp variable */ double two_over_T = 2*sample_rate; double two_over_T_squared = two_over_T * two_over_T; /* calculate digital filter coefficents */ /*w = 2.0*M_PI*fc; no pre-warping */ w = sample_rate*2.0*tan(M_PI*fc/sample_rate); /* pre-warping */ w_squared = w*w; den = two_over_T_squared + d*w*two_over_T + w_squared; filter2->a1 = 2.0*(-two_over_T_squared + w_squared)/den; filter2->a2 = (two_over_T_squared - d*w*two_over_T + w_squared)/den; switch (type) { case FILTER_LOWPASS: filter2->b0 = filter2->b2 = w_squared/den; filter2->b1 = 2.0*(filter2->b0); break; case FILTER_BANDPASS: filter2->b0 = d*w*two_over_T/den; filter2->b1 = 0.0; filter2->b2 = -(filter2->b0); break; case FILTER_HIGHPASS: filter2->b0 = filter2->b2 = two_over_T_squared/den; filter2->b1 = -2.0*(filter2->b0); break; default: logerror("filter2_setup() - Invalid filter type for 2nd order filter."); break; } filter2->b0 *= gain; filter2->b1 *= gain; filter2->b2 *= gain; } /* Reset the input/output voltages to 0. */ void filter2_reset(filter2_context *filter2) { filter2->x0 = 0; filter2->x1 = 0; filter2->x2 = 0; filter2->y0 = 0; filter2->y1 = 0; filter2->y2 = 0; } /* Step the filter. */ void filter2_step(filter2_context *filter2) { filter2->y0 = -filter2->a1 * filter2->y1 - filter2->a2 * filter2->y2 + filter2->b0 * filter2->x0 + filter2->b1 * filter2->x1 + filter2->b2 * filter2->x2; filter2->x2 = filter2->x1; filter2->x1 = filter2->x0; filter2->y2 = filter2->y1; filter2->y1 = filter2->y0; } /* Setup a filter2 structure based on an op-amp multipole bandpass circuit. */ void filter_opamp_m_bandpass_setup(device_t *device, double r1, double r2, double r3, double c1, double c2, filter2_context *filter2) { double r_in, fc, d, gain; if (r1 == 0) { logerror("filter_opamp_m_bandpass_setup() - r1 can not be 0"); return; /* Filter can not be setup. Undefined results. */ } if (r2 == 0) { gain = 1; r_in = r1; } else { gain = r2 / (r1 + r2); r_in = 1.0 / (1.0/r1 + 1.0/r2); } fc = 1.0 / (2 * M_PI * sqrt(r_in * r3 * c1 * c2)); d = (c1 + c2) / sqrt(r3 / r_in * c1 * c2); gain *= -r3 / r_in * c2 / (c1 + c2); filter2_setup(device, FILTER_BANDPASS, fc, d, gain, filter2); }