diff options
Diffstat (limited to 'Alc')
| -rw-r--r-- | Alc/uhjfilter.c | 91 | ||||
| -rw-r--r-- | Alc/uhjfilter.h | 49 |
2 files changed, 140 insertions, 0 deletions
diff --git a/Alc/uhjfilter.c b/Alc/uhjfilter.c new file mode 100644 index 00000000..63a88aa7 --- /dev/null +++ b/Alc/uhjfilter.c @@ -0,0 +1,91 @@ + +#include "config.h" + +#include "alu.h" +#include "uhjfilter.h" + +/* This is the maximum number of samples processed for each inner loop + * iteration. */ +#define MAX_UPDATE_SAMPLES 256 + + +static const ALfloat Filter1Coeff[4] = { + 0.6923878f, 0.9360654322959f, 0.9882295226860f, 0.9987488452737f +}; +static const ALfloat Filter2Coeff[4] = { + 0.4021921162426f, 0.8561710882420f, 0.9722909545651f, 0.9952884791278f +}; + +void EncodeUhj2(Uhj2Encoder *enc, ALfloat (*restrict OutBuffer)[BUFFERSIZE], ALfloat (*restrict InSamples)[BUFFERSIZE], ALuint SamplesToDo) +{ + ALuint base, i, c; + + for(base = 0;base < SamplesToDo;) + { + ALfloat D[MAX_UPDATE_SAMPLES], S; + ALuint todo = minu(SamplesToDo - base, MAX_UPDATE_SAMPLES); + + /* D = 0.6554516*Y */ + for(i = 0;i < todo;i++) + { + ALfloat in = 0.6554516f*InSamples[2][base+i]; + for(c = 0;c < 4;c++) + { + ALfloat aa = Filter1Coeff[c]*Filter1Coeff[c]; + ALfloat out = aa*(in + enc->Filter1_Y[c].y[1]) - enc->Filter1_Y[c].x[1]; + enc->Filter1_Y[c].x[1] = enc->Filter1_Y[c].x[0]; + enc->Filter1_Y[c].x[0] = in; + enc->Filter1_Y[c].y[1] = enc->Filter1_Y[c].y[0]; + enc->Filter1_Y[c].y[0] = out; + in = out; + } + /* NOTE: Filter1 requires a 1 sample delay for the base output, so + * take the sample before the last for output. + */ + D[i] = enc->Filter1_Y[3].y[1]; + } + + /* D += j(-0.3420201*W' + 0.5098604*X) */ + for(i = 0;i < todo;i++) + { + ALfloat in = -0.3420201f*1.414213562f*InSamples[0][base+i] + + 0.5098604f*InSamples[1][base+i]; + for(c = 0;c < 4;c++) + { + ALfloat aa = Filter2Coeff[c]*Filter2Coeff[c]; + ALfloat out = aa*(in + enc->Filter2_WX[c].y[1]) - enc->Filter2_WX[c].x[1]; + enc->Filter2_WX[c].x[1] = enc->Filter2_WX[c].x[0]; + enc->Filter2_WX[c].x[0] = in; + enc->Filter2_WX[c].y[1] = enc->Filter2_WX[c].y[0]; + enc->Filter2_WX[c].y[0] = out; + in = out; + } + D[i] += enc->Filter2_WX[3].y[0]; + } + + /* S = 0.9396926*W' + 0.1855740*X + * Left = (S + D)/2.0 + * Right = (S - D)/2.0 + */ + for(i = 0;i < todo;i++) + { + ALfloat in = 0.9396926f*1.414213562f*InSamples[0][base+i] + + 0.1855740f*InSamples[1][base+i]; + for(c = 0;c < 4;c++) + { + ALfloat aa = Filter1Coeff[c]*Filter1Coeff[c]; + ALfloat out = aa*(in + enc->Filter1_WX[c].y[1]) - enc->Filter1_WX[c].x[1]; + enc->Filter1_WX[c].x[1] = enc->Filter1_WX[c].x[0]; + enc->Filter1_WX[c].x[0] = in; + enc->Filter1_WX[c].y[1] = enc->Filter1_WX[c].y[0]; + enc->Filter1_WX[c].y[0] = out; + in = out; + } + S = enc->Filter1_WX[3].y[1]; + OutBuffer[0][base + i] += (S + D[i]) * 0.5f; + OutBuffer[1][base + i] += (S - D[i]) * 0.5f; + } + + base += todo; + } +} diff --git a/Alc/uhjfilter.h b/Alc/uhjfilter.h new file mode 100644 index 00000000..5238e202 --- /dev/null +++ b/Alc/uhjfilter.h @@ -0,0 +1,49 @@ +#ifndef UHJFILTER_H +#define UHJFILTER_H + +#include "AL/al.h" + +#include "alMain.h" + +typedef struct AllPassState { + ALfloat x[2]; /* Last two input samples */ + ALfloat y[2]; /* Last two output samples */ +} AllPassState; + +/* Encoding 2-channel UHJ from B-Format is done as: + * + * W' = W * sqrt(2) + * S = 0.9396926*W' + 0.1855740*X + * D = j(-0.3420201*W' + 0.5098604*X) + 0.6554516*Y + * + * Left = (S + D)/2.0 + * Right = (S - D)/2.0 + * + * where j is a wide-band +90 degree phase shift. + * + * The phase shift is done using a Hilbert transform, described here: + * https://web.archive.org/web/20060708031958/http://www.biochem.oulu.fi/~oniemita/dsp/hilbert/ + * It works using 2 sets of 4 chained filters. The first filter chain produces + * a phase shift of varying magnitude over a wide range of frequencies, while + * the second filter chain produces a phase shift 90 degrees ahead of the + * first over the same range. + * + * Combining these two stages requires the use of three filter chains. S- + * channel output uses a Filter1 chain on the W and X channel mix, while the D- + * channel output uses a Filter1 chain on the Y channel plus a Filter2 chain on + * the W and X channel mix. This results in the W and X input mix on the D- + * channel output having the required +90 degree phase shift relative to the + * other inputs. + */ + +typedef struct Uhj2Encoder { + AllPassState Filter1_WX[4]; + AllPassState Filter1_Y[4]; + AllPassState Filter2_WX[4]; +} Uhj2Encoder; + +/* Encodes a 2-channel UHJ (stereo-compatible) signal from a B-Format input + * signal. */ +void EncodeUhj2(Uhj2Encoder *enc, ALfloat (*restrict OutBuffer)[BUFFERSIZE], ALfloat (*restrict InSamples)[BUFFERSIZE], ALuint SamplesToDo); + +#endif /* UHJFILTER_H */ |