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https://github.com/radio95-rnt/fm95.git
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72 lines
2.4 KiB
C
72 lines
2.4 KiB
C
#include "filters.h"
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void init_preemphasis(ResistorCapacitor *filter, float tau, float sample_rate) {
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filter->prev_sample = 0.0f;
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filter->alpha = expf(-1 / (tau*sample_rate));
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filter->gain = 1.0f / sqrtf(1.0f - filter->alpha);
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}
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float apply_preemphasis(ResistorCapacitor *filter, float sample) {
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float out = (sample - filter->alpha * filter->prev_sample) * filter->gain;
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filter->prev_sample = sample;
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return out;
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}
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float hard_clip(float sample, float threshold) {
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return fmaxf(-threshold, fminf(threshold, sample));
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}
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void init_lpf(LPFFilter *filter, float cutoff, int sample_rate) {
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float a = tanf(M_PI * cutoff / sample_rate);
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float a2 = a * a;
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float r, e;
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for (int i = 0; i < LPF_ORDER; i++) {
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r = sinf(M_PI * (2.0f * i + 1.0f) / (4.0f * LPF_ORDER));
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e = a2 + 2.0f * a * r + 1.0f;
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float inv_e = 1.0f / e;
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filter->A[i] = a2 * inv_e;
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filter->d1[i] = 2.0f * (1.0f - a2) * inv_e;
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filter->d2[i] = -(a2 - 2.0f * a * r + 1.0f) * inv_e;
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}
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}
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float process_lpf(LPFFilter *filter, float x) {
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float y = x;
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#if USE_NEON // Use NEON if available
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float32x4_t v_y = vdupq_n_f32(y); // Load input into all lanes
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for (int i = 0; i < LPF_ORDER; i += 4) { // Process 4 biquads at a time
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float32x4_t v_w1 = vld1q_f32(&filter->w1[i]);
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float32x4_t v_w2 = vld1q_f32(&filter->w2[i]);
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float32x4_t v_d1 = vld1q_f32(&filter->d1[i]);
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float32x4_t v_d2 = vld1q_f32(&filter->d2[i]);
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float32x4_t v_A = vld1q_f32(&filter->A[i]);
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// Compute w0 = d1 * w1 + d2 * w2 + y
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float32x4_t v_w0 = vmlaq_f32(vmulq_f32(v_d1, v_w1), v_d2, v_w2);
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v_w0 = vaddq_f32(v_w0, v_y);
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// Compute y = A * (w0 + 2*w1 + w2)
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float32x4_t v_tw1 = vaddq_f32(v_w1, v_w1); // 2*w1
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float32x4_t v_sum = vaddq_f32(vaddq_f32(v_w0, v_tw1), v_w2);
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v_y = vmulq_f32(v_A, v_sum); // Multiply by A
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// Store updated values
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vst1q_f32(&filter->w2[i], v_w1);
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vst1q_f32(&filter->w1[i], v_w0);
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}
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return vgetq_lane_f32(v_y, 0); // Return first lane of vector
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#else // Scalar fallback if NEON is not available
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for (int i = 0; i < LPF_ORDER; i++) {
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float w0_new = filter->d1[i] * filter->w1[i] + filter->d2[i] * filter->w2[i] + y;
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y = filter->A[i] * (w0_new + 2.0f * filter->w1[i] + filter->w2[i]);
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filter->w2[i] = filter->w1[i];
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filter->w1[i] = w0_new;
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}
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return y;
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#endif
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} |