Alter how panpot/pair-wise panning works

This change allows pair-wise panning to mostly go through the normal ambisonic
panning methods, with one special-case. First, a term is added to the stereo
decoder matrix's X coefficient so that a centered sound is reduced by -3dB on
each output channel. Panning in front creates a similar gain response to the
typical
L = sqrt(1-pan)
R = sqrt(pan)
for pan = [0,1]. Panning behind the listener can reduce (up to) an additional
-10dB, creating a audible difference between front and back sounds as if
simulating head obstruction.

Secondly, as a special-case, the source positions are warped when calculating
the ambisonic coefficients so that full left panning is reached at -30 degrees
and full right at +30 degrees. This is to retain the expected 60-degree stereo
width. This warping does not apply to B-Format buffer input, although it
otherwise has the same gain responses.

1 files changed, 10 insertions, 0 deletions

diff --git a/OpenAL32/Include/alu.h b/OpenAL32/Include/alu.h
index c9f8760e..402c3181 100644
--- a/OpenAL32/Include/alu.h
+++ b/OpenAL32/Include/alu.h
@@ -297,6 +297,16 @@ inline void CalcXYZCoeffs(ALfloat x, ALfloat y, ALfloat z, ALfloat spread, ALflo
 void CalcAngleCoeffs(ALfloat azimuth, ALfloat elevation, ALfloat spread, ALfloat coeffs[MAX_AMBI_COEFFS]);
 
 /**
+ * CalcAnglePairwiseCoeffs
+ *
+ * Calculates ambisonic coefficients based on azimuth and elevation. The
+ * azimuth and elevation parameters are in radians, going right and up
+ * respectively. This pairwise variant warps the result such that +30 azimuth
+ * is full right, and -30 azimuth is full left.
+ */
+void CalcAnglePairwiseCoeffs(ALfloat azimuth, ALfloat elevation, ALfloat spread, ALfloat coeffs[MAX_AMBI_COEFFS]);
+
+/**
  * ComputeAmbientGains
  *
  * Computes channel gains for ambient, omni-directional sounds.