FMTools

lib/constants.h

@@ -0,0 +1,6 @@
+#ifndef PI
+#define PI 3.14159265358979323846
+#endif
+#ifndef M_2PI
+#define M_2PI (3.14159265358979323846 * 2.0)
+#endif

lib/filters.c

@@ -0,0 +1,41 @@
+#include "filters.h"
+
+void init_emphasis(Emphasis *pe, float tau, float sample_rate) {
+    pe->prev_sample = 0.0f;
+    pe->alpha = exp(-1 / (tau * sample_rate));
+}
+
+float apply_pre_emphasis(Emphasis *pe, float sample) {
+    float audio = sample-pe->alpha*pe->prev_sample;
+    pe->prev_sample = audio;
+    return audio*2;
+}
+
+void init_low_pass_filter(LowPassFilter *lp, float cutoff_frequency, float sample_rate) {
+    for (int i = 0; i < FIR_TAPS; i++) {
+        for (int j = 0; j < FIR_PHASES; j++) {
+            int mi = i * FIR_PHASES + j + 1;
+            float sincpos = mi - (((FIR_TAPS * FIR_PHASES) + 1.0f) / 2.0f);
+            float firlowpass = (sincpos == 0.0f) ? 1.0f : sinf(M_2PI * cutoff_frequency * sincpos / sample_rate) / (PI * sincpos);
+            float window = 0.54f - 0.46f * cosf(M_2PI * mi / (FIR_TAPS * FIR_PHASES)); // Hamming window
+            lp->low_pass_fir[j][i] = firlowpass * window;
+        }
+    }
+    memset(lp->sample_buffer, 0, sizeof(lp->sample_buffer));
+    lp->buffer_index = 0;
+}
+
+float apply_low_pass_filter(LowPassFilter *lp, float sample) {
+    // Update the sample buffer
+    lp->sample_buffer[lp->buffer_index] = sample;
+    lp->buffer_index = (lp->buffer_index + 1) % FIR_TAPS;
+
+    // Apply the filter
+    float result = 0.0f;
+    int index = lp->buffer_index;
+    for (int i = 0; i < FIR_TAPS; i++) {
+        result += lp->low_pass_fir[0][i] * lp->sample_buffer[index];
+        index = (index + 1) % FIR_TAPS;
+    }
+    return result*6;
+}

lib/filters.h

@@ -0,0 +1,23 @@
+#include "math.h"
+#include <string.h>
+#include "constants.h"
+
+#define FIR_PHASES 32
+#define FIR_TAPS 32
+
+typedef struct {
+    float alpha;
+    float prev_sample;
+} Emphasis;
+
+void init_emphasis(Emphasis *pe, float tau, float sample_rate);
+float apply_pre_emphasis(Emphasis *pe, float sample);
+
+typedef struct {
+    float low_pass_fir[FIR_PHASES][FIR_TAPS];
+    float sample_buffer[FIR_TAPS];
+    int buffer_index;
+} LowPassFilter;
+
+void init_low_pass_filter(LowPassFilter *lp, float cutoff_frequency, float sample_rate);
+float apply_low_pass_filter(LowPassFilter *lp, float sample);

lib/oscillator.c

@@ -0,0 +1,29 @@
+#include "oscillator.h"
+
+void init_oscillator(Oscillator *osc, float frequency, float sample_rate) {
+    osc->phase = 0.0f;
+    osc->phase_increment = (M_2PI * frequency) / sample_rate;
+    osc->sample_rate = sample_rate;
+}
+
+void change_oscillator_frequency(Oscillator *osc, float frequency) {
+    osc->phase_increment = (M_2PI * frequency) / osc->sample_rate;
+}
+
+float get_oscillator_sin_sample(Oscillator *osc) {
+    float sample = sinf(osc->phase);
+    osc->phase += osc->phase_increment;
+    if (osc->phase >= M_2PI) {
+        osc->phase -= M_2PI;
+    }
+    return sample;
+}
+
+float get_oscillator_cos_sample(Oscillator *osc) {
+    float sample = cosf(osc->phase);
+    osc->phase += osc->phase_increment;
+    if (osc->phase >= M_2PI) {
+        osc->phase -= M_2PI;
+    }
+    return sample;
+}

lib/oscillator.h

@@ -0,0 +1,13 @@
+#include "constants.h"
+#include "math.h"
+
+typedef struct {
+    float phase;
+    float phase_increment;
+    float sample_rate;
+} Oscillator;
+
+void init_oscillator(Oscillator *osc, float frequency, float sample_rate);
+void change_oscillator_frequency(Oscillator *osc, float frequency);
+float get_oscillator_sin_sample(Oscillator *osc);
+float get_oscillator_cos_sample(Oscillator *osc);