obs-filters: Add a simple 3-band equalizer

plugins/obs-filters/CMakeLists.txt

@@ -129,6 +129,7 @@ target_sources(
           color-key-filter.c
           color-grade-filter.c
           sharpness-filter.c
+          eq-filter.c
           gain-filter.c
           noise-gate-filter.c
           mask-filter.c

plugins/obs-filters/data/locale/en-US.ini

@@ -125,3 +125,7 @@ Greenscreen.Quality="Quality (higher GPU usage, better quality)"
 Greenscreen.Performance="Performance (lower GPU usage, good quality)"
 Greenscreen.Threshold="Threshold"
 Upward.Compressor="Upward Compressor"
+3BandEq="3-Band Equalizer"
+3BandEq.low="Low"
+3BandEq.mid="Mid"
+3BandEq.high="High"

plugins/obs-filters/eq-filter.c

@@ -0,0 +1,161 @@
+#include <media-io/audio-math.h>
+#include <util/circlebuf.h>
+#include <util/darray.h>
+#include <obs-module.h>
+
+#include <math.h>
+
+#define LOW_FREQ 800.0f
+#define HIGH_FREQ 5000.0f
+
+struct eq_channel_state {
+	float lf_delay0;
+	float lf_delay1;
+	float lf_delay2;
+	float lf_delay3;
+
+	float hf_delay0;
+	float hf_delay1;
+	float hf_delay2;
+	float hf_delay3;
+
+	float sample_delay1;
+	float sample_delay2;
+	float sample_delay3;
+};
+
+struct eq_data {
+	obs_source_t *context;
+	size_t channels;
+	struct eq_channel_state eqs[MAX_AUDIO_CHANNELS];
+	float lf;
+	float hf;
+	float low_gain;
+	float mid_gain;
+	float high_gain;
+};
+
+static const char *eq_name(void *unused)
+{
+	UNUSED_PARAMETER(unused);
+	return obs_module_text("3BandEq");
+}
+
+static void eq_update(void *data, obs_data_t *settings)
+{
+	struct eq_data *eq = data;
+	eq->low_gain = db_to_mul((float)obs_data_get_double(settings, "low"));
+	eq->mid_gain = db_to_mul((float)obs_data_get_double(settings, "mid"));
+	eq->high_gain = db_to_mul((float)obs_data_get_double(settings, "high"));
+}
+
+static void eq_defaults(obs_data_t *defaults)
+{
+	obs_data_set_default_double(defaults, "low", 0.0);
+	obs_data_set_default_double(defaults, "mid", 0.0);
+	obs_data_set_default_double(defaults, "high", 0.0);
+}
+
+static obs_properties_t *eq_properties(void *unused)
+{
+	obs_properties_t *props = obs_properties_create();
+	obs_property_t *p;
+
+#define make_db_slider(name)                                                  \
+	p = obs_properties_add_float_slider(props, name,                      \
+					    obs_module_text("3BandEq." name), \
+					    -20.0f, 20.0, 0.1);               \
+	obs_property_float_set_suffix(p, " dB");
+
+	make_db_slider("high");
+	make_db_slider("mid");
+	make_db_slider("low");
+#undef make_db_slider
+
+	UNUSED_PARAMETER(unused);
+	return props;
+}
+
+static void *eq_create(obs_data_t *settings, obs_source_t *filter)
+{
+	struct eq_data *eq = bzalloc(sizeof(*eq));
+	eq->channels = audio_output_get_channels(obs_get_audio());
+	eq->context = filter;
+
+	float freq = (float)audio_output_get_sample_rate(obs_get_audio());
+	eq->lf = 2.0f * sinf(M_PI * LOW_FREQ / freq);
+	eq->hf = 2.0f * sinf(M_PI * HIGH_FREQ / freq);
+
+	eq_update(eq, settings);
+	return eq;
+}
+
+static void eq_destroy(void *data)
+{
+	struct eq_data *eq = data;
+	bfree(eq);
+}
+
+#define EQ_EPSILON (1.0f / 4294967295.0f)
+
+static inline float eq_process(struct eq_data *eq, struct eq_channel_state *c,
+			       float sample)
+{
+	float l, m, h;
+
+	c->lf_delay0 += eq->lf * (sample - c->lf_delay0) + EQ_EPSILON;
+	c->lf_delay1 += eq->lf * (c->lf_delay0 - c->lf_delay1);
+	c->lf_delay2 += eq->lf * (c->lf_delay1 - c->lf_delay2);
+	c->lf_delay3 += eq->lf * (c->lf_delay2 - c->lf_delay3);
+
+	l = c->lf_delay3;
+
+	c->hf_delay0 += eq->hf * (sample - c->hf_delay0) + EQ_EPSILON;
+	c->hf_delay1 += eq->hf * (c->hf_delay0 - c->hf_delay1);
+	c->hf_delay2 += eq->hf * (c->hf_delay1 - c->hf_delay2);
+	c->hf_delay3 += eq->hf * (c->hf_delay2 - c->hf_delay3);
+
+	h = c->sample_delay3 - c->hf_delay3;
+	m = c->sample_delay3 - (h + l);
+
+	l *= eq->low_gain;
+	m *= eq->mid_gain;
+	h *= eq->high_gain;
+
+	c->sample_delay3 = c->sample_delay2;
+	c->sample_delay2 = c->sample_delay1;
+	c->sample_delay1 = sample;
+
+	return l + m + h;
+}
+
+static struct obs_audio_data *eq_filter_audio(void *data,
+					      struct obs_audio_data *audio)
+{
+	struct eq_data *eq = data;
+	const uint32_t frames = audio->frames;
+
+	for (size_t c = 0; c < eq->channels; c++) {
+		float *adata = (float *)audio->data[c];
+		struct eq_channel_state *channel = &eq->eqs[c];
+
+		for (size_t i = 0; i < frames; i++) {
+			adata[i] = eq_process(eq, channel, adata[i]);
+		}
+	}
+
+	return audio;
+}
+
+struct obs_source_info eq_filter = {
+	.id = "basic_eq_filter",
+	.type = OBS_SOURCE_TYPE_FILTER,
+	.output_flags = OBS_SOURCE_AUDIO,
+	.get_name = eq_name,
+	.create = eq_create,
+	.destroy = eq_destroy,
+	.update = eq_update,
+	.filter_audio = eq_filter_audio,
+	.get_defaults = eq_defaults,
+	.get_properties = eq_properties,
+};

plugins/obs-filters/obs-filters.c

@@ -11,6 +11,7 @@ extern struct obs_source_info mask_filter;
 extern struct obs_source_info mask_filter_v2;
 extern struct obs_source_info crop_filter;
 extern struct obs_source_info gain_filter;
+extern struct obs_source_info eq_filter;
 extern struct obs_source_info hdr_tonemap_filter;
 extern struct obs_source_info color_filter;
 extern struct obs_source_info color_filter_v2;
@@ -51,6 +52,7 @@ bool obs_module_load(void)
 	obs_register_source(&mask_filter_v2);
 	obs_register_source(&crop_filter);
 	obs_register_source(&gain_filter);
+	obs_register_source(&eq_filter);
 	obs_register_source(&hdr_tonemap_filter);
 	obs_register_source(&color_filter);
 	obs_register_source(&color_filter_v2);