audioconvert: add optional hilbert transform to rear channels

Add an option to do a hilbert transform on the generated rear channels
to do a 90 degree pahse shift on them. This can improve spacialization
of the rear channels.

See #861

src/daemon/client-rt.conf.in

@@ -87,4 +87,5 @@ stream.properties = {
     #channelmix.lfe-cutoff = 0
     #channelmix.rear-delay = 12.0
     #channelmix.stereo-widen = 0.0
+    #channelmix.hilbert-taps = 0
 }

src/daemon/client.conf.in

@@ -77,4 +77,5 @@ stream.properties = {
     #channelmix.lfe-cutoff = 0
     #channelmix.rear-delay = 12.0
     #channelmix.stereo-widen = 0.0
+    #channelmix.hilbert-taps = 0
 }

src/daemon/minimal.conf.in

@@ -208,6 +208,7 @@ context.objects = [
             #channelmix.lfe-cutoff  = 0
             #channelmix.rear-delay  = 12.0
             #channelmix.stereo-widen = 0.0
+            #channelmix.hilbert-taps = 0
             channelmix.disable     = true
             #node.param.Props      = {
             #    params = [
@@ -265,6 +266,7 @@ context.objects = [
             #channelmix.lfe-cutoff = 0
             #channelmix.rear-delay = 12.0
             #channelmix.stereo-widen = 0.0
+            #channelmix.hilbert-taps = 0
             channelmix.disable     = true
             #node.param.Props      = {
             #    params = [

src/daemon/pipewire-pulse.conf.in

@@ -87,6 +87,7 @@ stream.properties = {
     #channelmix.lfe-cutoff = 0
     #channelmix.rear-delay = 12.0
     #channelmix.stereo-widen = 0.0
+    #channelmix.hilbert-taps = 0
 }
 
 # client/stream specific properties