Audio: Selector: Add blob for stereo to double mono

This patch adds build of blob downmix_stereo_to_mono.conf. It
is useful for processing mono input for MFCC. The sum of left
and right multiplied by 0.5 is passed to both left and right
sink channels.

Signed-off-by: Seppo Ingalsuo <seppo.ingalsuo@linux.intel.com>

Author: singalsu

src/audio/selector/tune/sof_selector_blobs.m

@@ -23,6 +23,7 @@ function sof_selector_blobs()
 	IPC4_CHANNEL_CONFIG_STEREO = 1;
 	IPC4_CHANNEL_CONFIG_QUATRO = 5;
 	IPC4_CHANNEL_CONFIG_5_POINT_1 = 8;
+	IPC4_CHANNEL_CONFIG_DUAL_MONO = 9;
 	IPC4_CHANNEL_CONFIG_7_POINT_1 = 12;
 
 	% Matrix for 1:1 pass-through
@@ -39,6 +40,16 @@ function sof_selector_blobs()
 	sel.coeffs(1, 2) = 0.7071;
 	stereo_to_mono_pack8 = write_blob(sel, "downmix_stereo_to_mono");
 
+	% Stereo to mono downmix
+	sel.ch_count = [2 2];
+	sel.ch_config = [IPC4_CHANNEL_CONFIG_STEREO IPC4_CHANNEL_CONFIG_DUAL_MONO];
+	sel.coeffs = zeros(8,8);
+	sel.coeffs(1, 1) = 0.5;
+	sel.coeffs(1, 2) = 0.5;
+	sel.coeffs(2, 1) = 0.5;
+	sel.coeffs(2, 2) = 0.5;
+	stereo_to_doublemono_pack8 = write_blob(sel, "downmix_stereo_to_doublemono");
+
 	% 5.1 to stereo downmix
 	sel.ch_count = [6 2];
 	sel.ch_config = [IPC4_CHANNEL_CONFIG_5_POINT_1 IPC4_CHANNEL_CONFIG_STEREO];

tools/topology/topology2/include/components/micsel/downmix_stereo_to_doublemono.conf

@@ -0,0 +1,26 @@
+# Exported with script sof_selector_blobs.m 21-May-2026
+# cd tools/tune/selector; octave sof_selector_blobs.m
+Object.Base.data."selector_config" {
+	bytes "
+		0x53,0x4f,0x46,0x34,0x00,0x00,0x00,0x00,
+		0x84,0x00,0x00,0x00,0x01,0xd0,0x01,0x03,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x02,0x00,0x02,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x02,0x00,0x02,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+		0x00,0x00,0x00,0x00"
+}