Fix the data to decode ambisonic to surround speaker arrays

Use the correct channel order and normalization of the ambisonic
channels. Resonance Audio expects Ambix compatible ordering
(ie. ACN channel order) and normalization (SN3D).

Specify that we want that ordering in the script generating the
speaker data and normalize the factors correctly to SN3D.

Add hand coded handling for Mono, Stereo, 2Dot1, 3Dot0 and
3Dot1 speaker configurations as those do not cover the
area behind the listener and thus don't really qualify as
a surround configuration.

Change-Id: I905ddaa81938df918a460a7dea0526444836cdff
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

1 files changed, 22 insertions, 30 deletions

diff --git a/util/adt_generate_qt.m b/util/adt_generate_qt.m
index 45b3dcd03..8bb9497d3 100644
--- a/util/adt_generate_qt.m
+++ b/util/adt_generate_qt.m
@@ -98,34 +98,6 @@ function adt_generate_qt()
     fprintf(outfile, "\n\n");
     fprintf(outfile, "QT_BEGIN_NAMESPACE\n\n");
 
-    % cover top/bottom and back for mono and stereo
-    imag_speakers = [0,0,radius; 0,0,-radius; 0,radius,0; 0,-radius,0; -radius,0,0];
-
-    % Mono, one speaker up front
-    S = ambi_spkr_array(...
-        ... % array name
-        'mono', ...
-        ... % coordinate codes, unit codes
-        ... % Azimuth, Elevation, Radius; Degrees, Degrees, Meters
-        'AER', 'DDM', ...
-        ... % speaker name, [azimuth, elevation, radius]
-        'C',  [  0, 0, radius] ...
-    );
-    createDecoders(S, imag_speakers, outfile);
-
-    % Stereo, assume -30 and 30 degree speakers
-    S = ambi_spkr_array(...
-        'stereo', ...
-        'AER', 'DDM', ...
-        'L',  [  30, 0, radius], ...
-        'R',  [ -30, 0, radius] ...
-    );
-    createDecoders(S, imag_speakers, outfile);
-
-    S.lfeRow = 3;
-    S.name = "2dot1";
-    createDecoders(S, imag_speakers, outfile);
-
     % cover top/bottom for surround
     imag_speakers = [0,0,radius; 0,0,-radius];
 
@@ -197,6 +169,24 @@ function writeLFERow(outfile, m, suffix)
     fprintf(outfile, "// LFE\n");
 end
 
+function [n, m] = getnm(l)
+% Computes spherical harmonic degree and order from Ambisonic Channel Number.
+    n = floor(sqrt(l));
+    m = l-n.^2-n;
+end
+
+function channels = normalizeSN3D(channels)
+    for i = 1:columns(channels)
+        [n, m] = getnm(i-1);
+        if (m == 0)
+            factor = 1;
+        else
+            factor = sqrt(2 * factorial(n - abs(m)) / (factorial(n + abs(m))));
+        endif
+        channels(i) *= factor;
+    endfor
+end
+
 function writeMatrix(outfile, level, S, M, suffix)
     m = trimMatrix(M);
     hasLFE = isfield(S, "lfeRow");
@@ -208,7 +198,8 @@ function writeMatrix(outfile, level, S, M, suffix)
     fprintf(outfile, "// Decoder matrix for %s, ambisonic level %d\n", S.name, level);
     fprintf(outfile, "static constexpr float decoderMatrix_%s_%d_%s[%d*%d] = {\n", S.name, level, suffix, r, c);
     for i = 1:rows(S.id)
-        fprintf(outfile, "%ff, ", m(i, :));
+        channels = normalizeSN3D(m(i, :))
+        fprintf(outfile, "%ff, ", channels);
         fprintf(outfile, "// %s\n", S.id(i, 1){1});
         if (hasLFE && S.lfeRow == i + 1)
             writeLFERow(outfile, m, suffix);
@@ -218,7 +209,8 @@ function writeMatrix(outfile, level, S, M, suffix)
 end
 
 function createOneDecoder(S, imag_speakers, outfile, level)
-    [D,S,M,C] = ambi_run_allrad(S, level, imag_speakers, [S.name '_' int2str(level)], false, "amb", 1, 3);
+    ambi_order = ambi_channel_definitions_convention(level, 'ambix2011')
+    [D,S,M,C] = ambi_run_allrad(S, ambi_order, imag_speakers, [S.name '_' int2str(level)], false, "amb", 1, 3);
     writeMatrix(outfile, level, S, M.lf, "lf");
     m = ambi_apply_gamma(M.hf, D.hf_gains, C);
     writeMatrix(outfile, level, S, m, "hf");