filter-chain: add example upmix filter

Add an example filter of PSD upmixing, using filters, convolver and
delay to simulate the upmixing logic in audioconvert.

src/daemon/filter-chain/meson.build

@@ -9,6 +9,7 @@ conf_files = [
   [ 'sink-eq6.conf', 'sink-eq6.conf' ],
   [ 'sink-matrix-spatialiser.conf', 'sink-matrix-spatialiser.conf' ],
   [ 'source-rnnoise.conf', 'source-rnnoise.conf' ],
+  [ 'sink-upmix-5.1-filter.conf', 'sink-upmix-5.1-filter.conf' ],
 ]
 
 foreach c : conf_files

src/daemon/filter-chain/sink-upmix-5.1-filter.conf

@@ -0,0 +1,151 @@
+# Stereo to 5.1 upmix sink
+#
+# Copy this file into a conf.d/ directory such as
+# ~/.config/pipewire/filter-chain.conf.d/
+#
+context.modules = [
+    {   name = libpipewire-module-filter-chain
+        args = {
+            node.description = "Upmix Sink"
+            filter.graph = {
+                nodes = [
+                    {   type = builtin name = copyFL label = copy }
+                    {   type = builtin name = copyFR label = copy }
+                    {   type = builtin name = copyOFL label = copy }
+                    {   type = builtin name = copyOFR label = copy }
+		    {
+		        # this mixes the front left and right together
+			# for filtering the center and subwoofer signal-
+                        name   = mixF
+                        type   = builtin
+                        label  = mixer
+                        control = {
+                          "Gain 1" = 0.707
+                          "Gain 2" = 0.707
+                        }
+                    }
+                    {   
+		        # filtering of the FC and LFE channel. We use a 2 channel
+			# parametric equalizer with custom filters for each channel.
+			# This makes it possible to run the filters in parallel.
+                        type = builtin
+                        name = eq_FC_LFE
+                        label = param_eq
+                        config = {
+                            filters1 = [
+			       # FC is a crossover filter (with 2 lowpass biquads)
+                               { type = bq_lowpass freq = 12000 },
+                               { type = bq_lowpass freq = 12000 },
+                            ]
+                            filters2 = [
+			       # LFE is first a gain adjustment (with a highself) and
+			       # then a crossover filter (with 2 lowpass biquads)
+                               { type = bq_highshelf freq = 0 gain = -20.0 }, # gain -20dB
+                               { type = bq_lowpass freq = 120 },
+                               { type = bq_lowpass freq = 120 },
+                            ]
+		        }
+                    }
+		    {
+		        # for the rear channels, we subtract the front channels. Do this
+			# with a mixer with negative gain to flip the sign.
+                        name   = subR
+                        type   = builtin
+                        label  = mixer
+                        control = {
+                          "Gain 1" = 0.707
+                          "Gain 2" = -0.707
+                        }
+                    }
+                    {
+		        # a delay for the rear Left channel. This can be
+			# replaced with the convolver below. */
+                        type   = builtin
+                        name   = delayRL
+                        label  = delay
+                        config = { "max-delay" = 1 }
+                        control = { "Delay (s)" = 0.012 }
+                    }
+                    {
+		        # a delay for the rear Right channel. This can be
+			# replaced with the convolver below. */
+                        type   = builtin
+                        name   = delayRR
+                        label  = delay
+                        config = { "max-delay" = 1 }
+                        control = { "Delay (s)" = 0.012 }
+                    }
+                    {
+		        # an optional convolver with a hilbert curve to
+			# change the phase. It also has a delay, making the above
+			# left delay filter optional.
+                        type   = builtin
+                        name   = convRL
+                        label  = convolver
+                        config = {
+                            gain = 1.0
+			    delay = 0.012
+                            filename = "/hilbert"
+			    length = 33
+			}
+		    }
+                    {
+		        # an optional convolver with a hilbert curve to
+			# change the phase. It also has a delay, making the above
+			# right delay filter optional.
+                        type   = builtin
+                        name   = convRR
+                        label  = convolver
+                        config = {
+                            gain = -1.0
+			    delay = 0.012
+                            filename = "/hilbert"
+			    length = 33
+			}
+		    }
+                 ]
+                 links = [
+                     { output = "copyFL:Out"  input="mixF:In 1" }
+                     { output = "copyFR:Out"  input="mixF:In 2" }
+                     { output = "copyFL:Out"  input="copyOFR:In" }
+                     { output = "copyFR:Out"  input="copyOFL:In" }
+                     { output = "mixF:Out"  input="eq_FC_LFE:In 1" }
+                     { output = "mixF:Out"  input="eq_FC_LFE:In 2" }
+                     { output = "copyFL:Out"  input="subR:In 1" }
+                     { output = "copyFR:Out"  input="subR:In 2" }
+		     # here we can choose to just delay or also convolve
+		     #
+                     #{ output = "subR:Out"  input="delayRL:In" }
+                     #{ output = "subR:Out"  input="delayRR:In" }
+                     { output = "subR:Out"  input="convRL:In" }
+                     { output = "subR:Out"  input="convRR:In" }
+                 ]
+                 inputs = [ "copyFL:In" "copyFR:In" ]
+                 outputs = [ 
+		              "copyOFL:Out"
+			      "copyOFR:Out"
+		              "eq_FC_LFE:Out 1"
+			      "eq_FC_LFE:Out 2"
+		              # here we can choose to just delay or also convolve
+                              #
+		              #"delayRL:Out"
+			      #"delayRR:Out"
+		              "convRL:Out"
+			      "convRR:Out"
+			   ]
+            }
+            capture.props = {
+                node.name = "effect_input.upmix_5.1"
+                media.class = "Audio/Sink"
+                audio.position = [ FL FR ]
+            }
+            playback.props = {
+                node.name = "effect_output.upmix_5.1"
+                audio.position = [ FL FR FC LFE RL RR ]
+                stream.dont-remix = true
+                node.passive = true
+            }
+        }
+    }
+]
+