alc/uhjfilter.h

   1 #ifndef UHJFILTER_H
   2 #define UHJFILTER_H
   3
   4 #include <array>
   5
   6 #include "alcmain.h"
   7 #include "almalloc.h"
   8
   9
  10 /* Encoding 2-channel UHJ from B-Format is done as:
  11  *
  12  * S = 0.9396926*W + 0.1855740*X
  13  * D = j(-0.3420201*W + 0.5098604*X) + 0.6554516*Y
  14  *
  15  * Left = (S + D)/2.0
  16  * Right = (S - D)/2.0
  17  *
  18  * where j is a wide-band +90 degree phase shift.
  19  *
  20  * The phase shift is done using a FIR filter derived from an FFT'd impulse
  21  * with the desired shift.
  22  */
  23
  24 struct Uhj2Encoder {
  25     /* A particular property of the filter allows it to cover nearly twice its
  26      * length, so the filter size is also the effective delay (despite being
  27      * center-aligned).
  28      */
  29     constexpr static size_t sFilterSize{128};
  30
  31     /* Delays for the unfiltered signal. */
  32     alignas(16) std::array<float,sFilterSize> mMidDelay{};
  33     alignas(16) std::array<float,sFilterSize> mSideDelay{};
  34
  35     alignas(16) std::array<float,BUFFERSIZE+sFilterSize> mMid{};
  36     alignas(16) std::array<float,BUFFERSIZE+sFilterSize> mSide{};
  37
  38     /* History for the FIR filter. */
  39     alignas(16) std::array<float,sFilterSize*2 - 1> mSideHistory{};
  40
  41     alignas(16) std::array<float,BUFFERSIZE + sFilterSize*2> mTemp{};
  42
  43     /**
  44      * Encodes a 2-channel UHJ (stereo-compatible) signal from a B-Format input
  45      * signal. The input must use FuMa channel ordering and scaling.
  46      */
  47     void encode(FloatBufferLine &LeftOut, FloatBufferLine &RightOut,
  48         const FloatBufferLine *InSamples, const size_t SamplesToDo);
  49
  50     DEF_NEWDEL(Uhj2Encoder)
  51 };
  52
  53 #endif /* UHJFILTER_H */