New crossfeed algorithm for Rockbox: "Meier" crossfeed

Emulates the basic "Meier" crossfeed (2 capacitors, 3 resistors)
as discussed in
http://www.meier-audio.homepage.t-online.de/passivefilter.htm

This crossfeed blends a bit of low-pass filtered L signal into
the R signal (and vice versa) while adding about 300 us delay
to the crossfed-signal. A difference with the crossfeed already
present in rockbox, is that this algorithm keeps the total
spectrum flat (the one currently in rockbox accentuates
low-frequency signals, making it sound a bit muffled).

This implementation is quite lightweight, just 3 multiplies per
left-right pair of samples. Has a default C implementation and
optimized assembly versions for ARM and Coldfire.

The crossfeed effect is quite subtle and is noticeable mostly
one albums that have very strong left-right separation (e.g.
one instrument only on the left, another only on the right).

In the user interface, the new crossfeed option appears as
"Meier" and is not configureable. The existing crossfeed is
renamed to "Custom" as it allows itself to be customised.

There is no entry for the user manual yet.

Change-Id: Iaa100616fe0fcd7e16f08cdb9a7f41501973eee1

7 files changed, 45 insertions, 8 deletions

diff --git a/apps/lang/english.lang b/apps/lang/english.lang
index fc575a3..7366a80 100644
--- a/apps/lang/english.lang
+++ b/apps/lang/english.lang
@@ -13052,3 +13052,37 @@
     *: "Western European"
   </voice>
 </phrase>
+<phrase>
+  id: LANG_CROSSFEED_MEIER
+  desc: in sound settings
+  user: core
+  <source>
+    *: none
+    swcodec: "Simple (Meier)"
+  </source>
+  <dest>
+    *: none
+    swcodec: "Simple (Meier)"
+  </dest>
+  <voice>
+    *: none
+    swcodec: "Simple"
+  </voice>
+</phrase>
+<phrase>
+  id: LANG_CROSSFEED_CUSTOM
+  desc: in sound settings
+  user: core
+  <source>
+    *: none
+    swcodec: "Custom"
+  </source>
+  <dest>
+    *: none
+    swcodec: "Custom"
+  </dest>
+  <voice>
+    *: none
+    swcodec: "Custom"
+  </voice>
+</phrase>
diff --git a/apps/plugin.c b/apps/plugin.c
index afb336e..e0e565e 100644
--- a/apps/plugin.c
+++ b/apps/plugin.c
@@ -565,7 +565,7 @@ static const struct plugin_api rockbox_api = {
     audio_set_output_source,
     audio_set_input_source,
 #endif
-    dsp_crossfeed_enable,
+    dsp_set_crossfeed_type ,
     dsp_eq_enable,
     dsp_dither_enable,
 #ifdef HAVE_PITCHCONTROL
diff --git a/apps/plugin.h b/apps/plugin.h
index b1d3c16..bb27781 100644
--- a/apps/plugin.h
+++ b/apps/plugin.h
@@ -682,7 +682,7 @@ struct plugin_api {
     void (*audio_set_output_source)(int monitor);
     void (*audio_set_input_source)(int source, unsigned flags);
 #endif
-    void (*dsp_crossfeed_enable)(bool enable);
+    void (*dsp_set_crossfeed_type)(int type);
     void (*dsp_eq_enable)(bool enable);
     void (*dsp_dither_enable)(bool enable);
 #ifdef HAVE_PITCHCONTROL
diff --git a/apps/plugins/mpegplayer/mpeg_settings.c b/apps/plugins/mpegplayer/mpeg_settings.c
index 7f92fb7..bcef4c6 100644
--- a/apps/plugins/mpegplayer/mpeg_settings.c
+++ b/apps/plugins/mpegplayer/mpeg_settings.c
@@ -457,8 +457,9 @@ static void sync_audio_setting(int setting, bool global)
         break;
 
     case MPEG_AUDIO_CROSSFEED:
-        rb->dsp_crossfeed_enable((global || settings.crossfeed) ?
-                                 rb->global_settings->crossfeed : false);
+        rb->dsp_set_crossfeed_type((global || settings.crossfeed) ?
+                                   rb->global_settings->crossfeed :
+                                   CROSSFEED_TYPE_NONE);
         break;
 
     case MPEG_AUDIO_EQUALIZER:
diff --git a/apps/settings.c b/apps/settings.c
index d777eb1..3bf9c5b 100644
--- a/apps/settings.c
+++ b/apps/settings.c
@@ -979,7 +979,7 @@ void settings_apply(bool read_disk)
     audio_set_crossfade(global_settings.crossfade);
 #endif
     replaygain_update();
-    dsp_crossfeed_enable(global_settings.crossfeed);
+    dsp_set_crossfeed_type(global_settings.crossfeed);
     dsp_set_crossfeed_direct_gain(global_settings.crossfeed_direct_gain);
     dsp_set_crossfeed_cross_params(global_settings.crossfeed_cross_gain,
                                    global_settings.crossfeed_hf_attenuation,
diff --git a/apps/settings.h b/apps/settings.h
index 55d3344..ef0bae5 100644
--- a/apps/settings.h
+++ b/apps/settings.h
@@ -325,7 +325,7 @@ struct user_settings
     struct replaygain_settings replaygain_settings;
 
     /* Crossfeed */
-    bool crossfeed;                             /* enable crossfeed */
+    int crossfeed;                              /* crossfeed type */
     unsigned int crossfeed_direct_gain;         /* dB x 10 */
     unsigned int crossfeed_cross_gain;          /* dB x 10 */
     unsigned int crossfeed_hf_attenuation;      /* dB x 10 */
diff --git a/apps/settings_list.c b/apps/settings_list.c
index 10d00d5..accd51d 100644
--- a/apps/settings_list.c
+++ b/apps/settings_list.c
@@ -1402,8 +1402,10 @@ const struct settings_list settings[] = {
 #endif
 
     /* crossfeed */
-    OFFON_SETTING(F_SOUNDSETTING, crossfeed, LANG_CROSSFEED, false,
-                  "crossfeed", dsp_crossfeed_enable),
+    CHOICE_SETTING(F_SOUNDSETTING, crossfeed, LANG_CROSSFEED, 0,"crossfeed",
+                   "off,meier,custom", dsp_set_crossfeed_type, 3,
+                   ID2P(LANG_OFF), ID2P(LANG_CROSSFEED_MEIER),
+                   ID2P(LANG_CROSSFEED_CUSTOM)),
     INT_SETTING_NOWRAP(F_SOUNDSETTING, crossfeed_direct_gain,
                        LANG_CROSSFEED_DIRECT_GAIN, -15,
                        "crossfeed direct gain", UNIT_DB, -60, 0, 5,