Add Chorus DSP.

audio/dsp_filter.c

@@ -227,6 +227,7 @@ extern const struct dspfilter_implementation *echo_dspfilter_get_implementation(
 extern const struct dspfilter_implementation *phaser_dspfilter_get_implementation(dspfilter_simd_mask_t mask);
 extern const struct dspfilter_implementation *wahwah_dspfilter_get_implementation(dspfilter_simd_mask_t mask);
 extern const struct dspfilter_implementation *eq_dspfilter_get_implementation(dspfilter_simd_mask_t mask);
+extern const struct dspfilter_implementation *chorus_dspfilter_get_implementation(dspfilter_simd_mask_t mask);
 
 static const dspfilter_get_implementation_t dsp_plugs_builtin[] = {
    panning_dspfilter_get_implementation,
@@ -235,6 +236,7 @@ static const dspfilter_get_implementation_t dsp_plugs_builtin[] = {
    phaser_dspfilter_get_implementation,
    wahwah_dspfilter_get_implementation,
    eq_dspfilter_get_implementation,
+   chorus_dspfilter_get_implementation,
 };
 
 static bool append_plugs(rarch_dsp_filter_t *dsp)

audio/filters/Chorus.dsp

@@ -0,0 +1,14 @@
+filters = 1
+filter0 = chorus
+
+# Controls the base delay of the chorus (milliseconds).
+# chorus_delay_ms = 25.0
+#
+# Controls the depth of the delay. The delay will vary between delay_ms +/- depth_ms.
+# chorus_depth_ms = 1.0
+#
+# Frequency of LFO which controls delay.
+# chorus_lfo_freq = 0.5
+#
+# Controls dry/wet-ness of effect. 1.0 = full chorus, 0.0 = no chorus.
+# chorus_drywet = 0.8

audio/filters/chorus.c

@@ -0,0 +1,148 @@
+/*  RetroArch - A frontend for libretro.
+ *  Copyright (C) 2010-2014 - Hans-Kristian Arntzen
+ *
+ *  RetroArch is free software: you can redistribute it and/or modify it under the terms
+ *  of the GNU General Public License as published by the Free Software Found-
+ *  ation, either version 3 of the License, or (at your option) any later version.
+ *
+ *  RetroArch is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
+ *  without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+ *  PURPOSE.  See the GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along with RetroArch.
+ *  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "dspfilter.h"
+#include <math.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifndef M_PI
+#define M_PI 3.1415926535897932384626433832795
+#endif
+
+#define CHORUS_MAX_DELAY 4096
+#define CHORUS_DELAY_MASK (CHORUS_MAX_DELAY - 1)
+
+struct chorus_data
+{
+   float old[2][CHORUS_MAX_DELAY];
+   unsigned old_ptr;
+
+   float delay;
+   float depth;
+   float input_rate;
+   float mix_dry;
+   float mix_wet;
+   unsigned lfo_ptr;
+   unsigned lfo_period;
+};
+
+static void chorus_free(void *data)
+{
+   free(data);
+}
+
+static void chorus_process(void *data, struct dspfilter_output *output,
+      const struct dspfilter_input *input)
+{
+   unsigned i;
+   struct chorus_data *ch = (struct chorus_data*)data;
+
+   output->samples = input->samples;
+   output->frames  = input->frames;
+   float *out = output->samples;
+
+   for (i = 0; i < input->frames; i++, out += 2)
+   {
+      float in[2] = { out[0], out[1] };
+
+      float delay = ch->delay + ch->depth * sin((2.0 * M_PI * ch->lfo_ptr++) / ch->lfo_period);
+      delay *= ch->input_rate;
+      if (ch->lfo_ptr >= ch->lfo_period)
+         ch->lfo_ptr = 0;
+
+      unsigned delay_int = (unsigned)delay;
+      if (delay_int >= CHORUS_MAX_DELAY - 1)
+         delay_int = CHORUS_MAX_DELAY - 2;
+      float delay_frac = delay - delay_int;
+
+      ch->old[0][ch->old_ptr] = in[0];
+      ch->old[1][ch->old_ptr] = in[1];
+
+      float l_a = ch->old[0][(ch->old_ptr - delay_int - 0) & CHORUS_DELAY_MASK];
+      float l_b = ch->old[0][(ch->old_ptr - delay_int - 1) & CHORUS_DELAY_MASK];
+      float r_a = ch->old[1][(ch->old_ptr - delay_int - 0) & CHORUS_DELAY_MASK];
+      float r_b = ch->old[1][(ch->old_ptr - delay_int - 1) & CHORUS_DELAY_MASK];
+
+      // Lerp introduces aliasing of the chorus component, but doing full polyphase here is probably overkill.
+      float chorus_l = l_a * (1.0f - delay_frac) + l_b * delay_frac;
+      float chorus_r = r_a * (1.0f - delay_frac) + r_b * delay_frac;
+
+      out[0] = ch->mix_dry * in[0] + ch->mix_wet * chorus_l;
+      out[1] = ch->mix_dry * in[1] + ch->mix_wet * chorus_r;
+
+      ch->old_ptr = (ch->old_ptr + 1) & CHORUS_DELAY_MASK;
+      ch->lfo_ptr = (ch->lfo_ptr + 1) % ch->lfo_period;
+   }
+}
+
+static void *chorus_init(const struct dspfilter_info *info,
+      const struct dspfilter_config *config, void *userdata)
+{
+   struct chorus_data *ch = (struct chorus_data*)calloc(1, sizeof(*ch));
+   if (!ch)
+      return NULL;
+
+   float delay, depth, lfo_freq, drywet;
+   config->get_float(userdata, "delay_ms", &delay, 25.0f);
+   config->get_float(userdata, "depth_ms", &depth, 1.0f);
+   config->get_float(userdata, "lfo_freq", &lfo_freq, 0.5f);
+   config->get_float(userdata, "drywet", &drywet, 0.8f);
+
+   delay /= 1000.0f;
+   depth /= 1000.0f;
+
+   if (depth > delay)
+      depth = delay;
+
+   if (drywet < 0.0f)
+      drywet = 0.0f;
+   else if (drywet > 1.0f)
+      drywet = 1.0f;
+
+   ch->mix_dry = 1.0f - 0.5f * drywet;
+   ch->mix_wet = 0.5f * drywet;
+
+   ch->delay = delay;
+   ch->depth = depth;
+   ch->lfo_period = (1.0f / lfo_freq) * info->input_rate;
+   ch->input_rate = info->input_rate;
+   if (!ch->lfo_period)
+      ch->lfo_period = 1;
+   return ch;
+}
+
+static const struct dspfilter_implementation chorus_plug = {
+   chorus_init,
+   chorus_process,
+   chorus_free,
+
+   DSPFILTER_API_VERSION,
+   "Chorus",
+   "chorus",
+};
+
+#ifdef HAVE_FILTERS_BUILTIN
+#define dspfilter_get_implementation chorus_dspfilter_get_implementation
+#endif
+
+const struct dspfilter_implementation *dspfilter_get_implementation(dspfilter_simd_mask_t mask)
+{
+   (void)mask;
+   return &chorus_plug;
+}
+
+#undef dspfilter_get_implementation
+

griffin/griffin.c

@@ -481,6 +481,7 @@ FILTERS
 
 #include "../audio/filters/echo.c"
 #include "../audio/filters/eq.c"
+#include "../audio/filters/chorus.c"
 #include "../audio/filters/iir.c"
 #include "../audio/filters/panning.c"
 #include "../audio/filters/phaser.c"