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Add tremolo effect with LFO-modulated amplitude #45

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5 changes: 3 additions & 2 deletions Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -5,16 +5,17 @@ LDLIBS = -lm
PYTHON = python3
PLAY = ffplay -v fatal -nodisp -autoexit -f s32le -ar 48000 -ch_layout mono -i pipe:0

effects = flanger echo fm phaser discont am distortion
effects = flanger echo fm phaser discont am distortion tremolo
flanger_defaults = 0.6 0.6 0.6 0.6
echo_defaults = 0.3 0.3 0.3 0.3
fm_defaults = 0.25 0.25 0.5 0.5
am_defaults = 0.5 0.5 0.5 0.5
phaser_defaults = 0.3 0.3 0.5 0.5
discont_defaults = 0.8 0.1 0.2 0.2
distortion_defaults = 0.5 0.6 0.8 0.0
tremolo_defaults = 0.5 0.7 0.0 0.0

HEADERS = biquad.h discont.h distortion.h echo.h effect.h flanger.h fm.h gensin.h lfo.h phaser.h util.h process.h
HEADERS = biquad.h discont.h distortion.h echo.h effect.h flanger.h fm.h gensin.h lfo.h phaser.h process.h tremolo.h util.h

default:
@echo "Pick one of" $(effects)
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2 changes: 2 additions & 0 deletions convert.c
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Expand Up @@ -21,6 +21,7 @@
#include "phaser.h"
#include "discont.h"
#include "distortion.h"
#include "tremolo.h"

static void magnitude_init(float pot1, float pot2, float pot3, float pot4) {}
static float magnitude_step(float in) { return u32_to_fraction(magnitude); }
Expand All @@ -36,6 +37,7 @@ struct effect {
EFF(echo),
EFF(flanger),
EFF(phaser),
EFF(tremolo),

/* "Helper" effects */
EFF(am),
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41 changes: 41 additions & 0 deletions tremolo.h
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@@ -0,0 +1,41 @@
//
// Tremolo effect - amplitude modulation via LFO
//
// Classic guitar amp tremolo effect that modulates volume
// using a sine or triangle wave LFO.
//
static struct {
struct lfo_state lfo;
float depth;
enum lfo_type wave;
} tremolo;

static inline void tremolo_init(float pot1, float pot2, float pot3, float pot4)
{
// pot1: LFO rate (0.5 - 15 Hz)
float rate = 0.5 + pot1 * 14.5;
set_lfo_freq(&tremolo.lfo, rate);

// pot2: depth (0 - 100%)
tremolo.depth = pot2;

// pot3: waveform (0-0.5 = sine, 0.5-1 = triangle)
tremolo.wave = pot3 < 0.5 ? lfo_sinewave : lfo_triangle;

fprintf(stderr, "tremolo:");
fprintf(stderr, " rate=%g Hz", rate);
fprintf(stderr, " depth=%g", pot2);
fprintf(stderr, " wave=%s\n", pot3 < 0.5 ? "sine" : "triangle");
}

static inline float tremolo_step(float in)
{
// Get LFO value (-1 to 1), convert to gain multiplier
float lfo = lfo_step(&tremolo.lfo, tremolo.wave);

// Convert LFO to amplitude multiplier: 1 - depth*(1-lfo)/2
// When lfo=1, mult=1; when lfo=-1, mult=1-depth
float mult = 1.0f - tremolo.depth * (1.0f - lfo) * 0.5f;

return in * mult;
}