Connect up the ChannelsTogether option in R3 as well, to extend the channel lock range upward

rubberband/RubberBandStretcher.h

@@ -331,25 +331,30 @@ public:
      *   the others in the case where the pitch scale is exactly 1.0.
      *
      * 11. Flags prefixed \c OptionChannels control the method used
-     * for processing two-channel audio in the R2 engine.  These
+     * for processing two-channel stereo audio. These have different,
-     * options have no effect when using the R3 engine.  These options
+     * but related, effects in the R2 and R3 engines.  These options
      * may not be changed after construction.
      *
-     *   \li \c OptionChannelsApart - Each channel is processed
+     *   \li \c OptionChannelsApart - Channels are handled for maximum
-     *   individually, though timing is synchronised and phases are
+     *   individual fidelity, with less tight synchronisation. In the
-     *   synchronised at transients (depending on the OptionTransients
+     *   R3 engine, this means stereo synchronisation is maintained
-     *   setting).  This gives the highest quality for the individual
+     *   more closely for lower-frequency content than higher.  In R2,
-     *   channels but a relative lack of stereo focus and unrealistic
+     *   it means the stereo channels are processed individually and
-     *   increase in "width".  This is the default.
+     *   only synchronised at transients.  In both engines this gives
+     *   the highest quality for the individual channels but a more
+     *   diffuse stereo image and an unnatural increase in "width".
+     *   This option is the default.
      *
-     *   \li \c OptionChannelsTogether - The first two channels (where
+     *   \li \c OptionChannelsTogether - Channels are handled for
-     *   two or more are present) are considered to be a stereo pair
+     *   tighter synchronisation at the expense of individual
-     *   and are processed in mid-side format; mid and side are
+     *   fidelity. In the R3 engine, this means stereo synchronisation
-     *   processed individually, with timing synchronised and phases
+     *   is maintained more closely for the full frequency range. In
-     *   synchronised at transients (depending on the OptionTransients
+     *   R2, it means the first two channels are considered to be a
-     *   setting).  This usually leads to better focus in the centre
+     *   stereo pair and are processed in mid-side format, with mid
-     *   but a loss of stereo space and width.  Any channels beyond
+     *   and side processed as if they were separate channels before
-     *   the first two are processed individually.
+     *   being recombined.  This usually leads to better focus in the
+     *   centre but relatively less stereo space and width and lower
+     *   fidelity for individual channel content.
      *
      * Finally, flags prefixed \c OptionStretch are obsolete flags
      * provided for backward compatibility only. They are ignored by

src/finer/Guide.h

@@ -156,6 +156,7 @@ public:
                         double meanMagnitude,
                         int unityCount,
                         bool realtime,
+                        bool tighterChannelLock,
                         Guidance &guidance) const {
 
         bool hadPhaseReset = guidance.phaseReset.present;
@@ -191,7 +192,12 @@ public:
 
         guidance.channelLock.present = true;
         guidance.channelLock.f0 = 0.0;
-        guidance.channelLock.f1 = 600.0;
+
+        if (tighterChannelLock) {
+            guidance.channelLock.f1 = nyquist;
+        } else {
+            guidance.channelLock.f1 = 600.0;
+        }
 
         bool kick =
             (segmentation.percussiveBelow > 40.0) &&

src/finer/R3Stretcher.cpp

@@ -968,7 +968,10 @@ R3Stretcher::analyseChannel(int c, int inhop, int prevInhop, int prevOuthop)
     } else {
         m_unityCount = 0;
     }
-        
+
+    bool tighterChannelLock =
+        m_parameters.options & RubberBandStretcher::OptionChannelsTogether;
+    
     m_guide.updateGuidance(ratio,
                            prevOuthop,
                            classifyScale->mag.data(),
@@ -980,6 +983,7 @@ R3Stretcher::analyseChannel(int c, int inhop, int prevInhop, int prevOuthop)
                            v_mean(classifyScale->mag.data() + 1, classify/2),
                            m_unityCount,
                            isRealTime(),
+                           tighterChannelLock,
                            cd->guidance);
 /*
     if (c == 0) {