Add Hall type audio upmixing.

For stereo content: left is sent to left channels, right to right channels and a slight bias to center channel. Power levels are kept the same from original content.

Re-enable passive audio upmixing, old code was incorrect

Fixes #10751

mythtv/libs/libmythfreesurround/freesurround.cpp

@@ -42,6 +42,8 @@ static const unsigned default_block_size = SURROUND_BUFSIZE;
 // Gain of center and lfe channels in passive mode (sqrt 0.5)
 static const float center_level = 0.707107; 
 static const float m3db = 0.7071067811865476f;           // 3dB  = SQRT(2)
+static const float m6db = 0.5;                           // 6dB  = SQRT(4)
+static const float m7db = 0.44721359549996;              // 7dB  = SQRT(5)
 
 unsigned int block_size = default_block_size;
 
@@ -245,8 +247,14 @@ uint FreeSurround::putFrames(void* buffer, uint numFrames, uint numChannels)
             switch (surround_mode)
             {
                 case SurroundModePassive:
+                case SurroundModePassiveHall:
                     for (i = 0; i < numFrames && ic < bs; i++,ic++)
-                        bufs->l[ic] = bufs->c[ic] = bufs->r[ic] = samples[i];
+                    {
+                        // should be -7dB to keep power level the same
+                        // but we bump the level a tad.
+                        bufs->c[ic] = bufs->l[ic] = bufs->r[ic] = samples[i] * m6db;
+                        bufs->ls[ic] = bufs->rs[ic] = bufs->c[ic];
+                    }
                     process = false;
                     break;
                 default:
@@ -267,9 +275,24 @@ uint FreeSurround::putFrames(void* buffer, uint numFrames, uint numChannels)
                         float lt      = *samples++;
                         float rt      = *samples++;
                         bufs->l[ic]   = lt;
-                        bufs->lfe[ic] = bufs->c[ic]  = (lt+rt) * center_level;
+                        bufs->lfe[ic] = bufs->c[ic] = (lt+rt) * m3db;
                         bufs->r[ic]   = rt;
-                        bufs->ls[ic]  = bufs->rs[ic] = (lt-rt) * center_level;
+                        // surround channels receive out-of-phase
+                        bufs->ls[ic]  = (rt-lt) * 0.5;
+                        bufs->rs[ic]  = (lt-rt) * 0.5;
+                    }
+                    process = false;
+                    break;
+                case SurroundModePassiveHall:
+                    for (i = 0; i < numFrames && ic < bs; i++,ic++)
+                    {
+                        float lt      = *samples++;
+                        float rt      = *samples++;
+                        bufs->l[ic]   = lt * m3db;
+                        bufs->lfe[ic] = bufs->c[ic] = (lt+rt) * m3db;
+                        bufs->r[ic]   = rt * m3db;
+                        bufs->ls[ic]  = bufs->l[ic];
+                        bufs->rs[ic]  = bufs->r[ic];
                     }
                     process = false;
                     break;

mythtv/libs/libmythfreesurround/freesurround.h

@@ -30,7 +30,8 @@ class FreeSurround
     {
         SurroundModePassive,
         SurroundModeActiveSimple,
-        SurroundModeActiveLinear
+        SurroundModeActiveLinear,
+        SurroundModePassiveHall
     } SurroundMode;
 public:
     FreeSurround(uint srate, bool moviemode, SurroundMode mode);

mythtv/programs/mythfrontend/audiogeneralsettings.cpp

@@ -453,6 +453,8 @@ HostComboBox *AudioConfigSettings::AudioUpmixType()
 {
     HostComboBox *gc = new HostComboBox("AudioUpmixType",false);
     gc->setLabel(QObject::tr("Upmix Quality"));
+    gc->addSelection(QObject::tr("Passive"), "0");
+    gc->addSelection(QObject::tr("Hall"), "3");
     gc->addSelection(QObject::tr("Good"), "1");
     gc->addSelection(QObject::tr("Best"), "2", true);  // default
     gc->setHelpText(QObject::tr("Set the audio surround-upconversion quality."));