Add a dual-band ambisonic decoder

This uses a virtual B-Format buffer for mixing, and then uses a dual-band
decoder for improved positional quality. This currently only works with first-
order output since first-order input (from the AL_EXT_BFROMAT extension) would
not sound correct when fed through a second- or third-order decoder.

This also does not currently implement near-field compensation since near-field
rendering effects are not implemented.

1 files changed, 286 insertions, 0 deletions

diff --git a/Alc/bformatdec.c b/Alc/bformatdec.c
new file mode 100644
index 00000000..d917f803
--- /dev/null
+++ b/Alc/bformatdec.c
@@ -0,0 +1,286 @@
+
+#include "config.h"
+
+#include "bformatdec.h"
+#include "ambdec.h"
+#include "alu.h"
+
+
+typedef struct BandSplitter {
+    ALfloat coeff;
+    ALfloat lp_z1;
+    ALfloat lp_z2;
+    ALfloat hp_z1;
+} BandSplitter;
+
+static void bandsplit_init(BandSplitter *splitter, ALfloat freq_mult)
+{
+    ALfloat w = freq_mult * F_TAU;
+    ALfloat cw = cosf(w);
+    if(cw > FLT_EPSILON)
+        splitter->coeff = (sinf(w) - 1.0f) / cw;
+    else
+        splitter->coeff = cw * -0.5f;
+
+    splitter->lp_z1 = 0.0f;
+    splitter->lp_z2 = 0.0f;
+    splitter->hp_z1 = 0.0f;
+}
+
+static void bandsplit_process(BandSplitter *splitter, ALfloat *restrict hpout, ALfloat *restrict lpout,
+                              const ALfloat *input, ALuint count)
+{
+    ALfloat coeff, d, x;
+    ALuint i;
+
+    coeff = splitter->coeff*0.5f + 0.5f;
+    for(i = 0;i < count;i++)
+    {
+        x = input[i];
+
+        d = (x - splitter->lp_z1) * coeff;
+        x = splitter->lp_z1 + d;
+        splitter->lp_z1 = x + d;
+
+        d = (x - splitter->lp_z2) * coeff;
+        x = splitter->lp_z2 + d;
+        splitter->lp_z2 = x + d;
+
+        lpout[i] = x;
+    }
+
+    coeff = splitter->coeff;
+    for(i = 0;i < count;i++)
+    {
+        x = input[i];
+
+        d = x - coeff*splitter->hp_z1;
+        x = splitter->hp_z1 + coeff*d;
+        splitter->hp_z1 = d;
+
+        hpout[i] = x - lpout[i];
+    }
+}
+
+
+static const ALfloat UnitScale[MAX_AMBI_COEFFS] = {
+    1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f,
+    1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f
+};
+static const ALfloat SN3D2N3DScale[MAX_AMBI_COEFFS] = {
+    1.000000000f, /* ACN  0 (W), sqrt(1) */
+    1.732050808f, /* ACN  1 (Y), sqrt(3) */
+    1.732050808f, /* ACN  2 (Z), sqrt(3) */
+    1.732050808f, /* ACN  3 (X), sqrt(3) */
+    2.236067978f, /* ACN  4 (V), sqrt(5) */
+    2.236067978f, /* ACN  5 (T), sqrt(5) */
+    2.236067978f, /* ACN  6 (R), sqrt(5) */
+    2.236067978f, /* ACN  7 (S), sqrt(5) */
+    2.236067978f, /* ACN  8 (U), sqrt(5) */
+    2.645751311f, /* ACN  9 (Q), sqrt(7) */
+    2.645751311f, /* ACN 10 (O), sqrt(7) */
+    2.645751311f, /* ACN 11 (M), sqrt(7) */
+    2.645751311f, /* ACN 12 (K), sqrt(7) */
+    2.645751311f, /* ACN 13 (L), sqrt(7) */
+    2.645751311f, /* ACN 14 (N), sqrt(7) */
+    2.645751311f, /* ACN 15 (P), sqrt(7) */
+};
+static const ALfloat FuMa2N3DScale[MAX_AMBI_COEFFS] = {
+    1.414213562f, /* ACN  0 (W), sqrt(2) */
+    1.732050808f, /* ACN  1 (Y), sqrt(3) */
+    1.732050808f, /* ACN  2 (Z), sqrt(3) */
+    1.732050808f, /* ACN  3 (X), sqrt(3) */
+    1.936491673f, /* ACN  4 (V), sqrt(15)/2 */
+    1.936491673f, /* ACN  5 (T), sqrt(15)/2 */
+    2.236067978f, /* ACN  6 (R), sqrt(5) */
+    1.936491673f, /* ACN  7 (S), sqrt(15)/2 */
+    1.936491673f, /* ACN  8 (U), sqrt(15)/2 */
+    2.091650066f, /* ACN  9 (Q), sqrt(35/8) */
+    1.972026594f, /* ACN 10 (O), sqrt(35)/3 */
+    2.231093404f, /* ACN 11 (M), sqrt(224/45) */
+    2.645751311f, /* ACN 12 (K), sqrt(7) */
+    2.231093404f, /* ACN 13 (L), sqrt(224/45) */
+    1.972026594f, /* ACN 14 (N), sqrt(35)/3 */
+    2.091650066f, /* ACN 15 (P), sqrt(35/8) */
+};
+
+
+/* NOTE: Low-frequency (LF) fields and BandSplitter filters are unused with
+ * single-band decoding
+ */
+typedef struct BFormatDec {
+    alignas(16) ALfloat MatrixHF[MAX_OUTPUT_CHANNELS][MAX_AMBI_COEFFS];
+    alignas(16) ALfloat MatrixLF[MAX_OUTPUT_CHANNELS][MAX_AMBI_COEFFS];
+
+    BandSplitter XOver[MAX_AMBI_COEFFS];
+
+    ALfloat (*Samples)[BUFFERSIZE];
+    /* These two alias into Samples */
+    ALfloat (*SamplesHF)[BUFFERSIZE];
+    ALfloat (*SamplesLF)[BUFFERSIZE];
+
+    ALuint NumChannels;
+    ALboolean DualBand;
+} BFormatDec;
+
+BFormatDec *bformatdec_alloc()
+{
+    return al_calloc(16, sizeof(BFormatDec));
+}
+
+void bformatdec_free(BFormatDec *dec)
+{
+    if(dec)
+    {
+        al_free(dec->Samples);
+        dec->Samples = NULL;
+        dec->SamplesHF = NULL;
+        dec->SamplesLF = NULL;
+
+        memset(dec, 0, sizeof(*dec));
+        al_free(dec);
+    }
+}
+
+void bformatdec_reset(BFormatDec *dec, const AmbDecConf *conf, ALuint chancount, ALuint srate, const ALuint chanmap[MAX_OUTPUT_CHANNELS])
+{
+    const ALfloat *coeff_scale = UnitScale;
+    ALfloat ratio;
+    ALuint i;
+
+    al_free(dec->Samples);
+    dec->Samples = NULL;
+    dec->SamplesHF = NULL;
+    dec->SamplesLF = NULL;
+
+    dec->NumChannels = chancount;
+    dec->Samples = al_calloc(16, dec->NumChannels * conf->FreqBands *
+                                 sizeof(dec->Samples[0]));
+    dec->SamplesHF = dec->Samples;
+    dec->SamplesLF = dec->SamplesHF + dec->NumChannels;
+
+    if(conf->CoeffScale == ADS_SN3D)
+        coeff_scale = SN3D2N3DScale;
+    else if(conf->CoeffScale == ADS_FuMa)
+        coeff_scale = FuMa2N3DScale;
+
+    if(conf->FreqBands == 1)
+    {
+        dec->DualBand = AL_FALSE;
+        ratio = 1.0f;
+    }
+    else
+    {
+        dec->DualBand = AL_TRUE;
+
+        ratio = conf->XOverFreq / (ALfloat)srate;
+        for(i = 0;i < MAX_AMBI_COEFFS;i++)
+            bandsplit_init(&dec->XOver[i], ratio);
+
+        ratio = powf(10.0f, conf->XOverRatio / 40.0f);
+        memset(dec->MatrixLF, 0, sizeof(dec->MatrixLF));
+        for(i = 0;i < conf->NumSpeakers;i++)
+        {
+            ALuint chan = chanmap[i];
+            ALuint j, k = 0;
+
+            for(j = 0;j < 1;j++)
+            {
+                if((conf->ChanMask&(1<<j)))
+                    dec->MatrixLF[chan][j] = conf->LFMatrix[i][k++] / coeff_scale[j] *
+                                             conf->LFOrderGain[0] / ratio;
+            }
+            for(;j < 4;j++)
+            {
+                if((conf->ChanMask&(1<<j)))
+                    dec->MatrixLF[chan][j] = conf->LFMatrix[i][k++] / coeff_scale[j] *
+                                             conf->LFOrderGain[1] / ratio;
+            }
+            for(;j < 9;j++)
+            {
+                if((conf->ChanMask&(1<<j)))
+                    dec->MatrixLF[chan][j] = conf->LFMatrix[i][k++] / coeff_scale[j] *
+                                             conf->LFOrderGain[2] / ratio;
+            }
+            for(;j < 16;j++)
+            {
+                if((conf->ChanMask&(1<<j)))
+                    dec->MatrixLF[chan][j] = conf->LFMatrix[i][k++] / coeff_scale[j] *
+                                             conf->LFOrderGain[3] / ratio;
+            }
+        }
+    }
+
+    memset(dec->MatrixHF, 0, sizeof(dec->MatrixHF));
+    for(i = 0;i < conf->NumSpeakers;i++)
+    {
+        ALuint chan = chanmap[i];
+        ALuint j, k = 0;
+
+        for(j = 0;j < 1;j++)
+        {
+            if((conf->ChanMask&(1<<j)))
+                dec->MatrixHF[chan][j] = conf->HFMatrix[i][k++] / coeff_scale[j] *
+                                         conf->HFOrderGain[0] * ratio;
+        }
+        for(;j < 4;j++)
+        {
+            if((conf->ChanMask&(1<<j)))
+                dec->MatrixHF[chan][j] = conf->HFMatrix[i][k++] / coeff_scale[j] *
+                                         conf->HFOrderGain[1] * ratio;
+        }
+        for(;j < 9;j++)
+        {
+            if((conf->ChanMask&(1<<j)))
+                dec->MatrixHF[chan][j] = conf->HFMatrix[i][k++] / coeff_scale[j] *
+                                         conf->HFOrderGain[2] * ratio;
+        }
+        for(;j < 16;j++)
+        {
+            if((conf->ChanMask&(1<<j)))
+                dec->MatrixHF[chan][j] = conf->HFMatrix[i][k++] / coeff_scale[j] *
+                                         conf->HFOrderGain[3] * ratio;
+        }
+    }
+}
+
+
+static void apply_row(ALfloat *out, const ALfloat *mtx, ALfloat (*restrict in)[BUFFERSIZE], ALuint inchans, ALuint todo)
+{
+    ALuint c, i;
+
+    for(c = 0;c < inchans;c++)
+    {
+        ALfloat gain = mtx[c];
+        if(!(gain > GAIN_SILENCE_THRESHOLD))
+            continue;
+        for(i = 0;i < todo;i++)
+            out[i] += in[c][i] * gain;
+    }
+}
+
+void bformatdec_process(struct BFormatDec *dec, ALfloat (*restrict OutBuffer)[BUFFERSIZE], ALuint OutChannels, ALfloat (*restrict InSamples)[BUFFERSIZE], ALuint SamplesToDo)
+{
+    ALuint chan, i;
+
+    if(dec->DualBand)
+    {
+        for(i = 0;i < dec->NumChannels;i++)
+            bandsplit_process(&dec->XOver[i], dec->SamplesHF[i], dec->SamplesLF[i],
+                              InSamples[i], SamplesToDo);
+
+        for(chan = 0;chan < OutChannels;chan++)
+        {
+            apply_row(OutBuffer[chan], dec->MatrixHF[chan], dec->SamplesHF,
+                      dec->NumChannels, SamplesToDo);
+            apply_row(OutBuffer[chan], dec->MatrixLF[chan], dec->SamplesLF,
+                      dec->NumChannels, SamplesToDo);
+        }
+    }
+    else
+    {
+        for(chan = 0;chan < OutChannels;chan++)
+            apply_row(OutBuffer[chan], dec->MatrixHF[chan], InSamples,
+                      dec->NumChannels, SamplesToDo);
+    }
+}