zynaddsubfx

commit fc71427c9bf88f2e474cd525862120a05a281d19
parent 04c72d6cb90da482d11c9bedba58b950f4255023
Author: Ricard Wanderlof <polluxsynth@butoba.net>
Date:   Tue,  4 Jan 2022 20:24:13 +0100

Fix part mute in jack multi mode (#327)

When part was muted, it was still sent on the individual output channels
when operating in jack-multi mode, which resulted in the last audio
buffer that had been generated beeing looped.

This turned out to be slightly more complex to fix than expected.
First of all, when a part is muted, Part::AllNotesOff() is called,
which makes the next call to Part::ComputePartSmps() gracefully shut
down the part, clearing all notes, resetting the part insert effects,
and ramping down the signal to zero in the buffer being generated to
avoid clicks. However, as the code was written, ComputePartSmps() was
never called for a disabled part, so the graceful shutdown was not
executed until the part was subsequently enabled. So simply setting the
output buffer from the part to zero when the part is disabled is not
sufficient, as there will be a slight click when it is subsequently
re-enabled, and ComputePartSmps() finally gets a chance to go through
its shutdown sequence, after having essentially been in suspended
animation while the voice was disabled.

The solution is to always call ComputePartSmps(), which will then
internally decide when to execute the audio generation code or whether
to generate silence.

When generating the master audio bus, there are still a lot of places
where the audio is chopped off when Penabled for the part is set to
false, resulting in a more audible click than technically should be
necessary.  This could be addressed in a separate patch if needed.

Diffstat:
M
src/Misc/Master.cpp
 | 
5
+++--
M
src/Misc/Part.cpp
 | 
12
++++++++++++

2 files changed, 15 insertions(+), 2 deletions(-)
diff --git a/src/Misc/Master.cpp b/src/Misc/Master.cpp
@@ -1277,9 +1277,10 @@ bool Master::AudioOut(float *outr, float *outl)
     memset(outr, 0, synth.bufferbytes);
 
     //Compute part samples and store them part[npart]->partoutl,partoutr
+    //Note: We do this regardless if the part is enabled or not, to allow
+    //the part to graciously shut down when disabled.
     for(int npart = 0; npart < NUM_MIDI_PARTS; ++npart)
-        if(part[npart]->Penabled)
-            part[npart]->ComputePartSmps();
+        part[npart]->ComputePartSmps();
 
     //Insertion effects
     for(int nefx = 0; nefx < NUM_INS_EFX; ++nefx)
diff --git a/src/Misc/Part.cpp b/src/Misc/Part.cpp
@@ -994,6 +994,18 @@ void Part::AllNotesOff()
  */
 void Part::ComputePartSmps()
 {
+    /* When we are in the process of being disabled (Penabled set to false),
+     * AllNotesOff will be called, setting killallnotes, which causes all
+     * playing voices to terminate and the signal level being graciously
+     * muted during the course of the current buffer. After that, all
+     * subsequent output buffers will be set to 0 until we are enabled again.
+     */
+    if (!Penabled && !killallnotes) {
+        memset(partoutl, 0, synth.bufferbytes);
+        memset(partoutr, 0, synth.bufferbytes);
+        return;
+    }
+
     assert(partefx[0]);
     for(unsigned nefx = 0; nefx < NUM_PART_EFX + 1; ++nefx) {
         memset(partfxinputl[nefx], 0, synth.bufferbytes);