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.

The comment in blobs export is also updated to current path of
the script.

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 dual-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];
@@ -189,7 +200,7 @@ function write_8bit_packed(pack8, blobname)
 	blob8 = sof_selector_build_blob(pack8);
 	str_config = "selector_config";
 	str_exported = "Exported with script sof_selector_blobs.m";
-	str_howto = "cd tools/tune/selector; octave sof_selector_blobs.m";
+	str_howto = "cd src/audio/selector/tune; octave sof_selector_blobs.m";
 	sof_tools = '../../../../tools';
 	sof_tplg = fullfile(sof_tools, 'topology');
 	sof_tplg_selector = fullfile(sof_tplg, 'topology2/include/components/micsel');

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 src/audio/selector/tune; 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"
+}