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Fm synth #2

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a6ac0de
fix compile error; fix fonts issue; fix FM voice settings sync issue;
DJ-Von May 11, 2026
8240117
fix 'ratio' hint;
DJ-Von May 11, 2026
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126 changes: 104 additions & 22 deletions fm_synthesis/fm_synth.c
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@ typedef struct {
float freq;
float phase;
float betta;
float ratio;
float ratio;
WaveType fwave;
FModType type;
} FMod;
Expand Down Expand Up @@ -73,6 +73,7 @@ SDL_Rect button_add = {20, 20, 60, 40};
/* ==== octave ==== */
void octave_up();
void octave_down();
void sync_fmod_settings();

/* ==== poliphony ==== */
void init_voices();
Expand All @@ -94,6 +95,9 @@ void audio_callback(void *u, Uint8 *stream, int len);
void draw_text(SDL_Renderer *r, TTF_Font *f, int x, int y, const char *txt, SDL_Color c);
void draw_wave(SDL_Renderer *r);
void draw_keyboard_hint(SDL_Renderer *r, TTF_Font *font);
TTF_Font *open_font_fallback(const char *primary, const char *fallback1, const char *fallback2, int size);
TTF_Font *open_ui_font(int size);
TTF_Font *open_ui_font_bold(int size);


int main()
Expand All @@ -104,9 +108,8 @@ int main()
SDL_Window *win = SDL_CreateWindow("Subtractive Synth",
SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 700, 700, 0);
SDL_Renderer *ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED);

TTF_Font *font = TTF_OpenFont("/System/Library/Fonts/Supplemental/Arial.ttf", 18);
TTF_Font *font_main = TTF_OpenFont("/System/Library/Fonts/Supplemental/Arial Black.ttf", 18);
TTF_Font *font = open_ui_font(18);
TTF_Font *font_main = open_ui_font_bold(18);


SDL_AudioSpec spec = {0};
Expand Down Expand Up @@ -150,9 +153,9 @@ int main()

if (e.key.keysym.sym == SDLK_TAB)
voices[0].wave = (voices[0].wave + 1) % 4;
if (e.key.keysym.sym == SDLK_1)
if (e.key.keysym.sym == SDLK_1)
if(keymap[0].freq > 27.50f) octave_down();
if (e.key.keysym.sym == SDLK_2)
if (e.key.keysym.sym == SDLK_2)
if (keymap[0].freq < 1760.0) octave_up();

for (int i = 0; i < keymap_size; i++)
Expand All @@ -176,7 +179,7 @@ int main()

if (fmod_on == 1)
{
FMod *f = &fm;
FMod *f = &fm[0];

if (e.key.keysym.sym == SDLK_q) f->fwave = (f->fwave + 1) % 4;
if (e.key.keysym.sym == SDLK_w) f->type = (f->type + 1) % 2;
Expand All @@ -195,6 +198,8 @@ int main()
fmod_on = 0;
continue;
}

sync_fmod_settings();
}
}
if (e.type == SDL_KEYUP)
Expand Down Expand Up @@ -249,7 +254,7 @@ int main()
draw_text(ren, font, 30, y, buf, white);
}
else if (fmod_on == 1 && fm[0].type == HARMONIC)
{
{
char buf[128];
sprintf(buf, "Harmonic modulator");

Expand All @@ -264,9 +269,11 @@ int main()
draw_text(ren, font, 200, 640,
" + add modulator | 1/2 octave | ESC exit", white);

draw_text(ren, font, 70, 670,
"Q modulator waveform | W modulator type | arrows freq/amp | A/S ratio", white);

draw_text(ren, font, 70, 662,
"Q modulator waveform | W modulator type | arrows freq/amp", white);
draw_text(ren, font, 275, 684,
"E/R ratio", white);

draw_wave(ren);
draw_keyboard_hint(ren, font);

Expand All @@ -276,6 +283,11 @@ int main()
}

SDL_CloseAudio();
TTF_CloseFont(font);
TTF_CloseFont(font_main);
SDL_DestroyRenderer(ren);
SDL_DestroyWindow(win);
TTF_Quit();
SDL_Quit();
}
/* ==== octave ==== */
Expand All @@ -300,7 +312,7 @@ void octave_down()
void init_voices()
{
for (int i = 0; i < MAX_VOICES; i++)
{
{
voices[i].active = 0;
voices[i].wave = WAVE_SIN;
}
Expand All @@ -319,7 +331,7 @@ int alloc_voice()
for (int i = 0; i < MAX_VOICES; i++)
if (!voices[i].active)
return i;
return 0;
return 0;
}

int is_key_active(SDL_Keycode key)
Expand All @@ -342,6 +354,7 @@ float gen_voice(Voice *v)
if (v->wave == WAVE_SQUARE) return sinf(v->phase) > 0 ? 1.0f : -1.0f;
if (v->wave == WAVE_TRIANGLE) return asinf(sinf(v->phase)) * 2 / PI;
if (v->wave == WAVE_SAW) return 2.0f * (v->phase / (2 * PI)) - 1.0f;
return 0.0f;
}

/* ===== frequency modulation ===== */
Expand All @@ -350,11 +363,11 @@ float process_fmod(FMod *f, Voice *v)
{
f->phase += 2 * PI * f->freq / SAMPLE_RATE;
if (f->phase > 2 * PI) f->phase -= 2 * PI;

v->phase += 2 * PI * v->freq / SAMPLE_RATE;
if (v->phase > 2 * PI) v->phase -= 2 * PI;

float mod;
float mod = 0.0f;

if (f->fwave == WAVE_SIN) mod = sinf(f->phase);
if (f->fwave == WAVE_SQUARE) mod = (sinf(f->phase) > 0 ? 1.0f : -1.0f);
Expand All @@ -365,6 +378,35 @@ float process_fmod(FMod *f, Voice *v)
if (v->wave == WAVE_SQUARE) return sinf(v->phase + f->betta * mod) > 0 ? 1.0f : -1.0f;
if (v->wave == WAVE_TRIANGLE) return asinf(sinf(v->phase + f->betta * mod)) * 2 / PI;
if (v->wave == WAVE_SAW) return 2.0f * ((v->phase + f->betta * mod) / (2 * PI)) - 1.0f;
return 0.0f;
}

void sync_fmod_settings()
{
float base_freq = fm[0].freq;
float base_betta = fm[0].betta;
float base_ratio = fm[0].ratio;
WaveType base_fwave = fm[0].fwave;
FModType base_type = fm[0].type;

for (int i = 0; i < MAX_VOICES; i++)
{
fm[i].betta = base_betta;
fm[i].ratio = base_ratio;
fm[i].fwave = base_fwave;
fm[i].type = base_type;

if (!voices[i].active)
{
fm[i].freq = base_freq;
continue;
}

if (base_type == HARMONIC)
fm[i].freq = voices[i].freq * base_ratio;
else
fm[i].freq = base_freq;
}
}

void add_fmod()
Expand All @@ -378,12 +420,14 @@ void add_fmod()
fm[0].fwave = WAVE_SIN;
fm[0].type = INHARMONIC;

sync_fmod_settings();
fmod_on = 1;
}

/* ===== audio ===== */
void audio_callback(void *u, Uint8 *stream, int len)
{
(void)u;
float *buf = (float *)stream;
int samples = len / sizeof(float);

Expand All @@ -392,11 +436,11 @@ void audio_callback(void *u, Uint8 *stream, int len)
float s = 0.0f;

for (int v = 0; v < MAX_VOICES; v++)
{
{
if (!voices[v].active) continue;

if(fmod_on)
s += process_fmod(&fm, &voices[v]);
s += process_fmod(&fm[v], &voices[v]);
else if (voices[v].active)
s += gen_voice(&voices[v]);
}
Expand All @@ -413,14 +457,53 @@ void audio_callback(void *u, Uint8 *stream, int len)

void draw_text(SDL_Renderer *r, TTF_Font *f, int x, int y, const char *txt, SDL_Color c)
{
if (!f || !txt) return;

SDL_Surface *s = TTF_RenderText_Solid(f, txt, c);
if (!s) return;

SDL_Texture *t = SDL_CreateTextureFromSurface(r, s);
if (!t)
{
SDL_FreeSurface(s);
return;
}

SDL_Rect dst = {x, y, s->w, s->h};
SDL_RenderCopy(r, t, NULL, &dst);
SDL_FreeSurface(s);
SDL_DestroyTexture(t);
}

TTF_Font *open_font_fallback(const char *primary, const char *fallback1, const char *fallback2, int size)
{
TTF_Font *font = TTF_OpenFont(primary, size);
if (!font) font = TTF_OpenFont(fallback1, size);
if (!font) font = TTF_OpenFont(fallback2, size);
if (font) return font;
return NULL;
}

TTF_Font *open_ui_font(int size)
{
return open_font_fallback(
"/System/Library/Fonts/Supplemental/Arial.ttf",
"/usr/share/fonts/TTF/DejaVuSans.ttf",
"/usr/share/fonts/liberation/LiberationSans-Regular.ttf",
size
);
}

TTF_Font *open_ui_font_bold(int size)
{
return open_font_fallback(
"/System/Library/Fonts/Supplemental/Arial Black.ttf",
"/usr/share/fonts/TTF/DejaVuSans-Bold.ttf",
"/usr/share/fonts/liberation/LiberationSans-Bold.ttf",
size
);
}

void draw_wave(SDL_Renderer *r)
{
int ox = 10;
Expand Down Expand Up @@ -485,13 +568,13 @@ void draw_keyboard_hint(SDL_Renderer *r, TTF_Font *font)
const int black_pos[] = {0,2,3,5,6,7};
const char *black_labels[] = {"S","F","G","J","K","L"};

SDL_Keycode white_keys[] =
SDL_Keycode white_keys[] =
{
SDLK_z, SDLK_x, SDLK_c, SDLK_v, SDLK_b,
SDLK_n, SDLK_m, SDLK_COMMA, SDLK_PERIOD, SDLK_SLASH
};

SDL_Keycode black_keys[] =
SDL_Keycode black_keys[] =
{
SDLK_s, SDLK_f, SDLK_g, SDLK_j, SDLK_k, SDLK_l
};
Expand All @@ -508,7 +591,7 @@ void draw_keyboard_hint(SDL_Renderer *r, TTF_Font *font)
};

if (is_key_active(white_keys[i]))
SDL_SetRenderDrawColor(r, 194, 155, 162, 255);
SDL_SetRenderDrawColor(r, 194, 155, 162, 255);
else
SDL_SetRenderDrawColor(r, 230, 230, 230,255);

Expand Down Expand Up @@ -538,7 +621,7 @@ void draw_keyboard_hint(SDL_Renderer *r, TTF_Font *font)
};

if (is_key_active(black_keys[i]))
SDL_SetRenderDrawColor(r, 150, 120, 126,255);
SDL_SetRenderDrawColor(r, 150, 120, 126,255);
else
SDL_SetRenderDrawColor(r, 40,40,40,255);

Expand All @@ -554,4 +637,3 @@ void draw_keyboard_hint(SDL_Renderer *r, TTF_Font *font)
);
}
}