avfilter/af_agate: implement mode option

doc/filters.texi

@@ -1308,9 +1308,16 @@ Shorter signals than the chosen attack time will be left untouched.
 Set input level before filtering.
 Default is 1. Allowed range is from 0.015625 to 64.
 
+@item mode
+Set the mode of operation. Can be @code{upward} or @code{downward}.
+Default is @code{downward}. If set to @code{upward} mode, higher parts of signal
+will be amplified, expanding dynamic range in upward direction.
+Otherwise, in case of @code{downward} lower parts of signal will be reduced.
+
 @item range
 Set the level of gain reduction when the signal is below the threshold.
 Default is 0.06125. Allowed range is from 0 to 1.
+Setting this to 0 disables reduction and then filter behaves like expander.
 
 @item threshold
 If a signal rises above this level the gain reduction is released.
@@ -4331,9 +4338,16 @@ The filter accepts the following options:
 Set input level before filtering.
 Default is 1. Allowed range is from 0.015625 to 64.
 
+@item mode
+Set the mode of operation. Can be @code{upward} or @code{downward}.
+Default is @code{downward}. If set to @code{upward} mode, higher parts of signal
+will be amplified, expanding dynamic range in upward direction.
+Otherwise, in case of @code{downward} lower parts of signal will be reduced.
+
 @item range
 Set the level of gain reduction when the signal is below the threshold.
 Default is 0.06125. Allowed range is from 0 to 1.
+Setting this to 0 disables reduction and then filter behaves like expander.
 
 @item threshold
 If a signal rises above this level the gain reduction is released.

libavfilter/af_agate.c

@@ -47,11 +47,13 @@ typedef struct AudioGateContext {
     double range;
     int link;
     int detection;
+    int mode;
 
     double thres;
     double knee_start;
-    double lin_knee_stop;
     double knee_stop;
+    double lin_knee_start;
+    double lin_knee_stop;
     double lin_slope;
     double attack_coeff;
     double release_coeff;
@@ -65,6 +67,9 @@ typedef struct AudioGateContext {
 
 static const AVOption options[] = {
     { "level_in",  "set input level",        OFFSET(level_in),  AV_OPT_TYPE_DOUBLE, {.dbl=1},           0.015625,   64, A },
+    { "mode",      "set mode",               OFFSET(mode),      AV_OPT_TYPE_INT,    {.i64=0},           0, 1, A, "mode" },
+    {   "downward",0,                        0,                 AV_OPT_TYPE_CONST,  {.i64=0},           0, 0, A, "mode" },
+    {   "upward",  0,                        0,                 AV_OPT_TYPE_CONST,  {.i64=1},           0, 0, A, "mode" },
     { "range",     "set max gain reduction", OFFSET(range),     AV_OPT_TYPE_DOUBLE, {.dbl=0.06125},     0, 1, A },
     { "threshold", "set threshold",          OFFSET(threshold), AV_OPT_TYPE_DOUBLE, {.dbl=0.125},       0, 1, A },
     { "ratio",     "set ratio",              OFFSET(ratio),     AV_OPT_TYPE_DOUBLE, {.dbl=2},           1,  9000, A },
@@ -88,7 +93,6 @@ static int agate_config_input(AVFilterLink *inlink)
     AudioGateContext *s = ctx->priv;
     double lin_threshold = s->threshold;
     double lin_knee_sqrt = sqrt(s->knee);
-    double lin_knee_start;
 
     if (s->detection)
         lin_threshold *= lin_threshold;
@@ -96,9 +100,9 @@ static int agate_config_input(AVFilterLink *inlink)
     s->attack_coeff  = FFMIN(1., 1. / (s->attack * inlink->sample_rate / 4000.));
     s->release_coeff = FFMIN(1., 1. / (s->release * inlink->sample_rate / 4000.));
     s->lin_knee_stop = lin_threshold * lin_knee_sqrt;
-    lin_knee_start = lin_threshold / lin_knee_sqrt;
+    s->lin_knee_start = lin_threshold / lin_knee_sqrt;
     s->thres = log(lin_threshold);
-    s->knee_start = log(lin_knee_start);
+    s->knee_start = log(s->lin_knee_start);
     s->knee_stop = log(s->lin_knee_stop);
 
     return 0;
@@ -112,26 +116,26 @@ static int agate_config_input(AVFilterLink *inlink)
 
 static double output_gain(double lin_slope, double ratio, double thres,
                           double knee, double knee_start, double knee_stop,
-                          double lin_knee_stop, double range)
+                          double range, int mode)
 {
-    if (lin_slope < lin_knee_stop) {
-        double slope = log(lin_slope);
-        double tratio = ratio;
-        double gain = 0.;
-        double delta = 0.;
-
-        if (IS_FAKE_INFINITY(ratio))
-            tratio = 1000.;
-        gain = (slope - thres) * tratio + thres;
-        delta = tratio;
-
-        if (knee > 1. && slope > knee_start) {
+    double slope = log(lin_slope);
+    double tratio = ratio;
+    double gain = 0.;
+    double delta = 0.;
+
+    if (IS_FAKE_INFINITY(ratio))
+        tratio = 1000.;
+    gain = (slope - thres) * tratio + thres;
+    delta = tratio;
+
+    if (mode) {
+        if (knee > 1. && slope < knee_stop)
+            gain = hermite_interpolation(slope, knee_stop, knee_start, ((knee_stop - thres) * tratio  + thres), knee_start, delta, 1.);
+    } else {
+        if (knee > 1. && slope > knee_start)
             gain = hermite_interpolation(slope, knee_start, knee_stop, ((knee_start - thres) * tratio  + thres), knee_stop, delta, 1.);
-        }
-        return FFMAX(range, exp(gain - slope));
     }
-
-    return 1.;
+    return FFMAX(range, exp(gain - slope));
 }
 
 static void gate(AudioGateContext *s,
@@ -146,6 +150,7 @@ static void gate(AudioGateContext *s,
 
     for (n = 0; n < nb_samples; n++, src += inlink->channels, dst += inlink->channels, scsrc += sclink->channels) {
         double abs_sample = fabs(scsrc[0] * level_sc), gain = 1.0;
+        int detected;
 
         if (s->link == 1) {
             for (c = 1; c < sclink->channels; c++)
@@ -161,10 +166,16 @@ static void gate(AudioGateContext *s,
             abs_sample *= abs_sample;
 
         s->lin_slope += (abs_sample - s->lin_slope) * (abs_sample > s->lin_slope ? attack_coeff : release_coeff);
-        if (s->lin_slope > 0.0)
+
+        if (s->mode)
+            detected = s->lin_slope > s->lin_knee_start;
+        else
+            detected = s->lin_slope < s->lin_knee_stop;
+
+        if (s->lin_slope > 0.0 && detected)
             gain = output_gain(s->lin_slope, s->ratio, s->thres,
                                s->knee, s->knee_start, s->knee_stop,
-                               s->lin_knee_stop, s->range);
+                               s->range, s->mode);
 
         for (c = 0; c < inlink->channels; c++)
             dst[c] = src[c] * level_in * gain * makeup;