obs-filters: Add downward expander filter

The downward expander acts as an advanced gate with smoother effect
since it lowers the level instead of discarding audio when below the
threshold.

plugins/obs-filters/CMakeLists.txt

@@ -50,7 +50,8 @@ set(obs-filters_SOURCES
 	mask-filter.c
 	invert-audio-polarity.c
 	compressor-filter.c
-	limiter-filter.c)
+	limiter-filter.c
+	expander-filter.c)
 
 add_library(obs-filters MODULE
 	${obs-filters_SOURCES}

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

@@ -79,3 +79,16 @@ Compressor.SidechainSource="Sidechain/Ducking Source"
 Limiter="Limiter"
 Limiter.Threshold="Threshold (dB)"
 Limiter.ReleaseTime="Release (ms)"
+Expander="Expander"
+Expander.Ratio="Ratio (X:1)"
+Expander.Threshold="Threshold (dB)"
+Expander.AttackTime="Attack (ms)"
+Expander.ReleaseTime="Release (ms)"
+Expander.OutputGain="Output Gain (dB)"
+Expander.Detector="Detection"
+Expander.RMS="RMS"
+Expander.Peak="Peak"
+Expander.None="None"
+Expander.Presets="Presets"
+Expander.Presets.Expander="Expander"
+Expander.Presets.Gate="Gate"

plugins/obs-filters/expander-filter.c

@@ -0,0 +1,407 @@
+#include <stdint.h>
+#include <inttypes.h>
+#include <math.h>
+
+#include <obs-module.h>
+#include <media-io/audio-math.h>
+#include <util/platform.h>
+#include <util/circlebuf.h>
+#include <util/threading.h>
+
+/* -------------------------------------------------------- */
+
+#define do_log(level, format, ...) \
+	blog(level, "[expander: '%s'] " format, \
+			obs_source_get_name(cd->context), ##__VA_ARGS__)
+
+#define warn(format, ...)  do_log(LOG_WARNING, format, ##__VA_ARGS__)
+#define info(format, ...)  do_log(LOG_INFO,    format, ##__VA_ARGS__)
+
+#ifdef _DEBUG
+#define debug(format, ...) do_log(LOG_DEBUG,   format, ##__VA_ARGS__)
+#else
+#define debug(format, ...)
+#endif
+
+/* -------------------------------------------------------- */
+
+#define S_RATIO                         "ratio"
+#define S_THRESHOLD                     "threshold"
+#define S_ATTACK_TIME                   "attack_time"
+#define S_RELEASE_TIME                  "release_time"
+#define S_OUTPUT_GAIN                   "output_gain"
+#define S_DETECTOR                      "detector"
+#define S_PRESETS                       "presets"
+
+#define MT_ obs_module_text
+#define TEXT_RATIO                      MT_("expander.Ratio")
+#define TEXT_THRESHOLD                  MT_("expander.Threshold")
+#define TEXT_ATTACK_TIME                MT_("expander.AttackTime")
+#define TEXT_RELEASE_TIME               MT_("expander.ReleaseTime")
+#define TEXT_OUTPUT_GAIN                MT_("expander.OutputGain")
+#define TEXT_DETECTOR                   MT_("expander.Detector")
+#define TEXT_PEAK                       MT_("expander.Peak")
+#define TEXT_RMS                        MT_("expander.RMS")
+#define TEXT_NONE                       MT_("expander.None")
+#define TEXT_PRESETS                    MT_("expander.Presets")
+#define TEXT_PRESETS_EXP                MT_("expander.Presets.Expander")
+#define TEXT_PRESETS_GATE               MT_("expander.Presets.Gate")
+
+#define MIN_RATIO                       1.0
+#define MAX_RATIO                       20.0
+#define MIN_THRESHOLD_DB                -60.0
+#define MAX_THRESHOLD_DB                0.0f
+#define MIN_OUTPUT_GAIN_DB              -32.0
+#define MAX_OUTPUT_GAIN_DB              32.0
+#define MIN_ATK_RLS_MS                  1
+#define MAX_RLS_MS                      1000
+#define MAX_ATK_MS                      100
+#define DEFAULT_AUDIO_BUF_MS            10
+
+#define MS_IN_S                         1000
+#define MS_IN_S_F                       ((float)MS_IN_S)
+
+/* -------------------------------------------------------- */
+
+struct expander_data {
+	obs_source_t *context;
+	float *envelope_buf;
+	size_t envelope_buf_len;
+
+	float ratio;
+	float threshold;
+	float attack_gain;
+	float release_gain;
+	float output_gain;
+
+	size_t num_channels;
+	size_t sample_rate;
+	float envelope;
+	float slope;
+	int  detector;
+	float runave;
+	bool is_gate;
+	float *runaverage;
+	size_t runaverage_len;
+	float *maxspl;
+	size_t maxspl_len;
+	float *env_in;
+	size_t env_in_len;
+};
+
+enum {
+	RMS_DETECT,
+	RMS_STILLWELL_DETECT,
+	PEAK_DETECT,
+	NO_DETECT,
+};
+/* -------------------------------------------------------- */
+
+static void resize_env_buffer(struct expander_data *cd, size_t len)
+{
+	cd->envelope_buf_len = len;
+	cd->envelope_buf = brealloc(cd->envelope_buf, len * sizeof(float));
+}
+
+static void resize_runaverage_buffer(struct expander_data *cd, size_t len)
+{
+	cd->runaverage_len = len;
+	cd->runaverage = brealloc(cd->runaverage, len * sizeof(float));
+}
+
+static void resize_maxspl_buffer(struct expander_data *cd, size_t len)
+{
+	cd->maxspl_len = len;
+	cd->maxspl = brealloc(cd->maxspl, len * sizeof(float));
+}
+
+static void resize_env_in_buffer(struct expander_data *cd, size_t len)
+{
+	cd->env_in_len = len;
+	cd->env_in = brealloc(cd->env_in, len * sizeof(float));
+}
+
+static inline float gain_coefficient(uint32_t sample_rate, float time)
+{
+	return (float)exp(-1.0f / (sample_rate * time));
+}
+
+static const char *expander_name(void *unused)
+{
+	UNUSED_PARAMETER(unused);
+	return obs_module_text("Expander");
+}
+
+static void expander_defaults(obs_data_t *s)
+{
+	const char *presets = obs_data_get_string(s, S_PRESETS);
+	bool is_expander_preset = true;
+	if (strcmp(presets, "gate") == 0)
+		is_expander_preset = false;
+	obs_data_set_default_string(s, S_PRESETS, is_expander_preset ?
+			"expander" : "gate");
+	obs_data_set_default_double(s, S_RATIO, is_expander_preset ?
+			2.0 : 10.0);
+	obs_data_set_default_double(s, S_THRESHOLD, -40.0f);
+	obs_data_set_default_int(s, S_ATTACK_TIME, 10);
+	obs_data_set_default_int(s, S_RELEASE_TIME, is_expander_preset ?
+			50 : 125);
+	obs_data_set_default_double(s, S_OUTPUT_GAIN, 0.0);
+	obs_data_set_default_string(s, S_DETECTOR, "RMS");
+}
+
+static void expander_update(void *data, obs_data_t *s)
+{
+	struct expander_data *cd = data;
+	const char *presets = obs_data_get_string(s, S_PRESETS);
+	if (strcmp(presets, "expander") == 0 && cd->is_gate) {
+		obs_data_clear(s);
+		obs_data_set_string(s, S_PRESETS, "expander");
+		expander_defaults(s);
+		cd->is_gate = false;
+	}
+	if (strcmp(presets, "gate") == 0 && !cd->is_gate) {
+		obs_data_clear(s);
+		obs_data_set_string(s, S_PRESETS, "gate");
+		expander_defaults(s);
+		cd->is_gate = true;
+	}
+
+	const uint32_t sample_rate =
+			audio_output_get_sample_rate(obs_get_audio());
+	const size_t num_channels =
+			audio_output_get_channels(obs_get_audio());
+	const float attack_time_ms =
+			(float)obs_data_get_int(s, S_ATTACK_TIME);
+	const float release_time_ms =
+			(float)obs_data_get_int(s, S_RELEASE_TIME);
+	const float output_gain_db =
+			(float)obs_data_get_double(s, S_OUTPUT_GAIN);
+
+	cd->ratio = (float)obs_data_get_double(s, S_RATIO);
+
+	cd->threshold = (float)obs_data_get_double(s, S_THRESHOLD);
+	cd->attack_gain = gain_coefficient(sample_rate,
+			attack_time_ms / MS_IN_S_F);
+	cd->release_gain = gain_coefficient(sample_rate,
+			release_time_ms / MS_IN_S_F);
+	cd->output_gain = db_to_mul(output_gain_db);
+	cd->num_channels = num_channels;
+	cd->sample_rate = sample_rate;
+	cd->slope = 1.0f - cd->ratio;
+
+	const char *detect_mode = obs_data_get_string(s, S_DETECTOR);
+	if (strcmp(detect_mode, "RMS") == 0)
+		cd->detector = RMS_DETECT;
+	if (strcmp(detect_mode, "peak") == 0)
+		cd->detector = PEAK_DETECT;
+	if (strcmp(detect_mode, "none") == 0)
+		cd->detector = NO_DETECT;
+
+	size_t sample_len = sample_rate * DEFAULT_AUDIO_BUF_MS / MS_IN_S;
+	if (cd->envelope_buf_len == 0)
+		resize_env_buffer(cd, sample_len);
+	if (cd->runaverage_len == 0)
+		resize_runaverage_buffer(cd, sample_len);
+	if (cd->maxspl_len == 0)
+		resize_maxspl_buffer(cd, sample_len);
+	if (cd->env_in_len == 0)
+		resize_env_in_buffer(cd, sample_len);
+}
+
+static void *expander_create(obs_data_t *settings, obs_source_t *filter)
+{
+	struct expander_data *cd = bzalloc(sizeof(struct expander_data));
+	cd->context = filter;
+	cd->runave = 0;
+	cd->is_gate = false;
+	const char *presets = obs_data_get_string(settings, S_PRESETS);
+	if (strcmp(presets, "gate") == 0)
+		cd->is_gate = true;
+
+	expander_update(cd, settings);
+	return cd;
+}
+
+static void expander_destroy(void *data)
+{
+	struct expander_data *cd = data;
+
+	bfree(cd->envelope_buf);
+	bfree(cd->runaverage);
+	bfree(cd->maxspl);
+	bfree(cd->env_in);
+	bfree(cd);
+}
+
+static void analyze_envelope(struct expander_data *cd,
+	float **samples, const uint32_t num_samples)
+{
+	if (cd->envelope_buf_len < num_samples) {
+		resize_env_buffer(cd, num_samples);
+	}
+	if (cd->runaverage_len < num_samples) {
+		resize_runaverage_buffer(cd, num_samples);
+	}
+	if (cd->maxspl_len < num_samples) {
+		resize_maxspl_buffer(cd, num_samples);
+	}
+	if (cd->env_in_len < num_samples) {
+		resize_env_in_buffer(cd, num_samples);
+	}
+
+	const float attack_gain = cd->attack_gain;
+	const float release_gain = cd->release_gain;
+	// 10 ms RMS window
+	const float rmscoef = exp2f((float)-100.0 / (float)cd->sample_rate);
+	// 2.5 microsec Peak window
+	const float peakcoef = exp2f((float)-1000.0 /((float)0.0025 *
+			(float)cd->sample_rate));
+
+	memset(cd->envelope_buf, 0, num_samples * sizeof(cd->envelope_buf[0]));
+	memset(cd->runaverage, 0, num_samples * sizeof(cd->runaverage[0]));
+	memset(cd->maxspl, 0, num_samples * sizeof(cd->maxspl[0]));
+	memset(cd->env_in, 0, num_samples * sizeof(cd->env_in[0]));
+
+	for (size_t chan = 0; chan < cd->num_channels; ++chan) {
+		if (!samples[chan])
+			continue;
+
+		float *envelope_buf = cd->envelope_buf;
+		float *runave = cd->runaverage;
+		float *maxspl = cd->maxspl;
+		float *env_in = cd->env_in;
+		float env = cd->envelope;
+		float RMSdet = 0;
+
+		runave[0] = cd->runave;
+		maxspl[0] = fabsf(samples[chan][0]);
+		env_in[0] = sqrtf(fmaxf(cd->runave, 0));
+
+		if (cd->detector == RMS_DETECT)
+			for (uint32_t i = 1; i < num_samples; ++i) {
+				runave[i] = rmscoef * runave[i - 1] +
+						(1 - rmscoef) *
+						powf(samples[chan][i], 2.0);
+				env_in[i] = sqrtf(runave[i]);
+			}
+		else if (cd->detector == PEAK_DETECT)
+			for (uint32_t i = 1; i < num_samples; ++i) {
+				maxspl[i] = powf(fmaxf(fabsf(maxspl[i - 1]),
+						fabsf(samples[chan][i])), 2);
+				runave[i] = peakcoef * runave[i - 1] +
+						(1 - peakcoef) * maxspl[i];
+				env_in[i] = sqrtf(runave[i]);
+			}
+		else if (cd->detector == NO_DETECT)
+			for (uint32_t i = 1; i < num_samples; ++i) {
+				runave[i] = powf(samples[chan][i], 2);
+				env_in[i] = fabsf(samples[chan][i]);
+			}
+		cd->runave = runave[num_samples-1];
+
+		for (uint32_t i = 0; i < num_samples; ++i) {
+
+			if (env < env_in[i]) {
+				env = env_in[i] + attack_gain
+						* (env - env_in[i]);
+			} else {
+				env = env_in[i] + release_gain
+						* (env - env_in[i]);
+			}
+			envelope_buf[i] = fmaxf(envelope_buf[i], env);
+		}
+
+	}
+	cd->envelope = cd->envelope_buf[num_samples - 1];
+}
+
+static inline void process_expansion(const struct expander_data *cd,
+	float **samples, uint32_t num_samples)
+{
+	for (size_t i = 0; i < num_samples; ++i) {
+		float env_db = mul_to_db(cd->envelope_buf[i]);
+		float gain = fmaxf(cd->slope * (cd->threshold - env_db),
+				-60.0);
+		gain = db_to_mul(fminf(0, gain));
+
+		for (size_t c = 0; c < cd->num_channels; ++c) {
+			if (samples[c]) {
+				samples[c][i] *= gain * cd->output_gain;
+			}
+		}
+	}
+}
+
+static struct obs_audio_data *expander_filter_audio(void *data,
+	struct obs_audio_data *audio)
+{
+	struct expander_data *cd = data;
+
+	const uint32_t num_samples = audio->frames;
+	if (num_samples == 0)
+		return audio;
+
+	float **samples = (float**)audio->data;
+
+	analyze_envelope(cd, samples, num_samples);
+	process_expansion(cd, samples, num_samples);
+	return audio;
+}
+
+static bool presets_changed(obs_properties_t *props, obs_property_t *prop,
+	obs_data_t *settings)
+{
+	return true;
+}
+
+static obs_properties_t *expander_properties(void *data)
+{
+	struct expander_data *cd = data;
+	obs_properties_t *props = obs_properties_create();
+	obs_source_t *parent = NULL;
+
+	if (cd)
+		parent = obs_filter_get_parent(cd->context);
+
+	obs_property_t *presets = obs_properties_add_list(props, S_PRESETS,
+			TEXT_PRESETS, OBS_COMBO_TYPE_LIST,
+			OBS_COMBO_FORMAT_STRING);
+	obs_property_list_add_string(presets, TEXT_PRESETS_EXP, "expander");
+	obs_property_list_add_string(presets, TEXT_PRESETS_GATE, "gate");
+	obs_property_set_modified_callback(presets, presets_changed);
+	obs_properties_add_float_slider(props, S_RATIO,
+			TEXT_RATIO, MIN_RATIO, MAX_RATIO, 0.1);
+	obs_properties_add_float_slider(props, S_THRESHOLD,
+			TEXT_THRESHOLD, MIN_THRESHOLD_DB, MAX_THRESHOLD_DB,
+			0.1);
+	obs_properties_add_int_slider(props, S_ATTACK_TIME,
+			TEXT_ATTACK_TIME, MIN_ATK_RLS_MS, MAX_ATK_MS, 1);
+	obs_properties_add_int_slider(props, S_RELEASE_TIME,
+			TEXT_RELEASE_TIME, MIN_ATK_RLS_MS, MAX_RLS_MS, 1);
+	obs_properties_add_float_slider(props, S_OUTPUT_GAIN,
+			TEXT_OUTPUT_GAIN, MIN_OUTPUT_GAIN_DB,
+			MAX_OUTPUT_GAIN_DB, 0.1);
+	obs_property_t *detect = obs_properties_add_list(props, S_DETECTOR,
+			TEXT_DETECTOR, OBS_COMBO_TYPE_LIST,
+			OBS_COMBO_FORMAT_STRING);
+	obs_property_list_add_string(detect, TEXT_RMS, "RMS");
+	obs_property_list_add_string(detect, TEXT_PEAK, "peak");
+	obs_property_list_add_string(detect, TEXT_NONE, "none");
+
+	UNUSED_PARAMETER(data);
+	return props;
+}
+
+struct obs_source_info expander_filter = {
+	.id = "expander_filter",
+	.type = OBS_SOURCE_TYPE_FILTER,
+	.output_flags = OBS_SOURCE_AUDIO,
+	.get_name = expander_name,
+	.create = expander_create,
+	.destroy = expander_destroy,
+	.update = expander_update,
+	.filter_audio = expander_filter_audio,
+	.get_defaults = expander_defaults,
+	.get_properties = expander_properties,
+};

plugins/obs-filters/obs-filters.c

@@ -27,6 +27,7 @@ extern struct obs_source_info invert_polarity_filter;
 extern struct obs_source_info noise_gate_filter;
 extern struct obs_source_info compressor_filter;
 extern struct obs_source_info limiter_filter;
+extern struct obs_source_info expander_filter;
 
 bool obs_module_load(void)
 {
@@ -49,5 +50,6 @@ bool obs_module_load(void)
 	obs_register_source(&noise_gate_filter);
 	obs_register_source(&compressor_filter);
 	obs_register_source(&limiter_filter);
+	obs_register_source(&expander_filter);
 	return true;
 }