As explained in the previous paper, these elements are additionally multiplied by the "tv
matrix" correction, which reduces the amplitude when the steering in near the middle.
This factor shows up in the figure below as a valley centered on zero steering.
As of 7/31/97 the "tv matrix" correction has been modified to depend only on the
absolute value of lr when cs is frontal. This will cause the surface above to remain at .71
along the lr=0 axis in the front. In this front direction the correction for TV Matrix
becomes tvcorr(|lr|). Tvcorr(|lr|) is -3dB at zero, and 1 when |lr| is 22.5 degrees and
higher.
The rear matrix elements during rear steering
The rear matrix elements given in the ’91 patent were not appropriate to a 5 channel
decoder, and were modified heuristically in our CP-3 product. The AES paper presented
a mathematical method to derive these elements along the boundary of the left rear
quadrant. The method worked along the boundary, but resulted in discontinuities along
the lr=0 axis, and along the cs=0 axis. In March of 1997 these discontinuities were
repaired (mostly) by additional corrections to the matrix elements, which preserved their
behavior along the steering boundaries.
For the new elements described here these errors have been corrected, first by using an
interpolation along the cs=0 boundary for LRL, where the value is made to match the
value of GS(lr) when cs is zero, and smoothly rises to the value given by the previous
math as cs increases negatively toward the rear. In the newest software LRR interpolates
along the cs=0 axis to GR(lr).
Left side/rear outputs during rear steering from Right to Right Rear
Let’s consider first the Left Rear Left and Left Rear Right matrix elements when the
steering is neutral or anywhere between full right and right rear. That is, lr can vary from
0 to –45 degrees, and cs can vary from 0 to –22.5 degrees.
Under these conditions the steered component of the input should be removed from the
left outputs - there should be no output from the rear left channel when the steering is
toward the right or right rear.
The matrix elements given in the ’91 patent achieve this goal. They are essentially the
same as the rear matrix elements in the 4 channel decoder, with the addition of the
sin(cs)+ cos(cs) correction for the unsteered loudness. When this is done the matrix
elements are simple. We will define two new functions, which are simply equal to sin,
and cosine of cs over this range.
LRL = cos(-cs) = sri(-cs)
