[MPlayer-cvslog] CVS: main/libaf af_hrtf.c, 1.6, 1.7 af_hrtf.h, 1.4, 1.5
Jindrich Makovicka CVS
syncmail at mplayerhq.hu
Mon Apr 11 16:01:32 CEST 2005
CVS change done by Jindrich Makovicka CVS
Update of /cvsroot/mplayer/main/libaf
In directory mail:/var2/tmp/cvs-serv28239
Modified Files:
af_hrtf.c af_hrtf.h
Log Message:
More HRTF enhancements
- a passive locking mechanism to enable the matrix to switch between active
and passive mode, which enhances the stereo image.
- a center front cancellation algorithm that damps the cross-talk if the
sound is coming predominantly from center (e.g. if there is dialogue).
These two new features should enhance the quality of surround downmix
noticeably.
Also a correction to the active gain control is included. The previous
implementation of Lt + Rt/Lt - Rt AGC should be fine in most cases, but the
calculation was inconsistent (gain unitarity is not guaranteed to be
preserved).
Signed off by Yue Shi Lai <ylai at users.sourceforge.net>
Index: af_hrtf.c
===================================================================
RCS file: /cvsroot/mplayer/main/libaf/af_hrtf.c,v
retrieving revision 1.6
retrieving revision 1.7
diff -u -r1.6 -r1.7
--- af_hrtf.c 10 Apr 2005 08:47:16 -0000 1.6
+++ af_hrtf.c 11 Apr 2005 14:01:29 -0000 1.7
@@ -88,6 +88,16 @@
return 0;
}
+/* Fuzzy matrix coefficient transfer function to "lock" the matrix on
+ a effectively passive mode if the gain is approximately 1 */
+inline float passive_lock(float x)
+{
+ const float x1 = x - 1;
+ const float ax1s = fabs(x - 1) * (1.0 / MATAGCLOCK);
+
+ return x1 - x1 / (1 + ax1s * ax1s) + 1;
+}
+
/* Unified active matrix decoder for 2 channel matrix encoded surround
sources */
inline void matrix_decode(short *in, const int k, const int il,
@@ -105,13 +115,22 @@
(1 + l_fwr + l_fwr);
float r_gain = (l_fwr + r_fwr) /
(1 + r_fwr + r_fwr);
- float lpr_gain = (lpr_fwr + lmr_fwr) /
+ /* The 2nd axis has strong gain fluctuations, and therefore require
+ limits. The factor corresponds to the 1 / amplification of (Lt
+ - Rt) when (Lt, Rt) is strongly correlated. (e.g. during
+ dialogues). It should be bigger than -12 dB to prevent
+ distortion. */
+ float lmr_lim_fwr = lmr_fwr > M9_03DB * lpr_fwr ?
+ lmr_fwr : M9_03DB * lpr_fwr;
+ float lpr_gain = (lpr_fwr + lmr_lim_fwr) /
(1 + lpr_fwr + lpr_fwr);
- float lmr_gain = (lpr_fwr + lmr_fwr) /
+ float lmr_gain = (lpr_fwr + lmr_lim_fwr) /
+ (1 + lmr_lim_fwr + lmr_lim_fwr);
+ float lmr_unlim_gain = (lpr_fwr + lmr_fwr) /
(1 + lmr_fwr + lmr_fwr);
float lpr, lmr;
float l_agc, r_agc, lpr_agc, lmr_agc;
- float f, d_gain;
+ float f, d_gain, c_gain, c_agc_cfk;
#if 0
static int counter = 0;
@@ -119,8 +138,9 @@
if(counter == 0)
fp_out = fopen("af_hrtf.log", "w");
- fprintf(fp_out, "%g %g %g %g %g ", counter * (1.0 / 48000),
- l_gain, r_gain, lpr_gain, lmr_gain);
+ if(counter % 240 == 0)
+ fprintf(fp_out, "%g %g %g %g %g ", counter * (1.0 / 48000),
+ l_gain, r_gain, lpr_gain, lmr_gain);
#endif
/*** AXIS NO. 1: (Lt, Rt) -> (C, Ls, Rs) ***/
@@ -132,8 +152,8 @@
*adapt_l_gain = (1 - f) * *adapt_l_gain + f * l_gain;
*adapt_r_gain = (1 - f) * *adapt_r_gain + f * r_gain;
/* Matrix */
- l_agc = in[il] * *adapt_l_gain;
- r_agc = in[ir] * *adapt_r_gain;
+ l_agc = in[il] * passive_lock(*adapt_l_gain);
+ r_agc = in[ir] * passive_lock(*adapt_r_gain);
cf[k] = (l_agc + r_agc) * M_SQRT1_2;
if(decode_rear) {
lr[kr] = rr[kr] = (l_agc - r_agc) * M_SQRT1_2;
@@ -150,29 +170,39 @@
lpr = (in[il] + in[ir]) * M_SQRT1_2;
lmr = (in[il] - in[ir]) * M_SQRT1_2;
/* AGC adaption */
- d_gain = (fabs(lpr_gain - *adapt_lpr_gain) +
- fabs(lmr_gain - *adapt_lmr_gain)) * 0.5;
+ d_gain = fabs(lmr_unlim_gain - *adapt_lmr_gain);
f = d_gain * (1.0 / MATAGCTRIG);
f = MATAGCDECAY - MATAGCDECAY / (1 + f * f);
*adapt_lpr_gain = (1 - f) * *adapt_lpr_gain + f * lpr_gain;
*adapt_lmr_gain = (1 - f) * *adapt_lmr_gain + f * lmr_gain;
- /* The 2nd axis has strong gain fluctuations, and therefore require
- limits. The factor is tricky. I think 2 is the reasonable
- value here, which phase inverts the L, R channel if Lt, Rt is
- strongly correlated (e.g. during dialogues) (1 would inhibit the
- steering behavior, > 4 appears to result in distortions). */
- if(*adapt_lmr_gain > 2 * *adapt_lpr_gain)
- *adapt_lmr_gain = 2 * *adapt_lpr_gain;
/* Matrix */
- lpr_agc = lpr * *adapt_lpr_gain;
- lmr_agc = lmr * *adapt_lmr_gain;
+ lpr_agc = lpr * passive_lock(*adapt_lpr_gain);
+ lmr_agc = lmr * passive_lock(*adapt_lmr_gain);
lf[k] = (lpr_agc + lmr_agc) * M_SQRT1_2;
rf[k] = (lpr_agc - lmr_agc) * M_SQRT1_2;
+ /*** CENTER FRONT CANCELLATION ***/
+ /* A heuristic approach exploits that Lt + Rt gain contains the
+ information about Lt, Rt correlation. This effectively reshapes
+ the front and rear "cones" to concentrate Lt + Rt to C and
+ introduce Lt - Rt in L, R. */
+ /* 0.67677 is the emprical lower bound for lpr_gain. */
+ c_gain = 8 * (*adapt_lpr_gain - 0.67677);
+ c_gain = c_gain > 0 ? c_gain : 0;
+ /* c_gain should not be too high, not even reaching full
+ cancellation (~ 0.50 - 0.55 at current AGC implementation), or
+ the center will s0und too narrow. */
+ c_gain = MATCOMPGAIN / (1 + c_gain * c_gain);
+ c_agc_cfk = c_gain * cf[k];
+ lf[k] -= c_agc_cfk;
+ rf[k] -= c_agc_cfk;
+ cf[k] += c_agc_cfk + c_agc_cfk;
#if 0
- fprintf(fp_out, "%g %g %g %g\n",
- *adapt_l_gain, *adapt_r_gain,
- *adapt_lpr_gain, *adapt_lmr_gain);
+ if(counter % 240 == 0)
+ fprintf(fp_out, "%g %g %g %g %g\n",
+ *adapt_l_gain, *adapt_r_gain,
+ *adapt_lpr_gain, *adapt_lmr_gain,
+ c_gain);
counter++;
#endif
}
Index: af_hrtf.h
===================================================================
RCS file: /cvsroot/mplayer/main/libaf/af_hrtf.h,v
retrieving revision 1.4
retrieving revision 1.5
diff -u -r1.4 -r1.5
--- af_hrtf.h 10 Apr 2005 08:47:16 -0000 1.4
+++ af_hrtf.h 11 Apr 2005 14:01:29 -0000 1.5
@@ -4,6 +4,7 @@
/* Amplitude scaling factors */
#define M17_0DB 0.1414213562
+#define M9_03DB 0.3535533906
#define M6_99DB 0.4472135955
#define M4_77DB 0.5773502692
#define M3_01DB 0.7071067812
@@ -25,6 +26,10 @@
#define MATAGCTRIG 8.0 /* (Fuzzy) AGC trigger */
#define MATAGCDECAY 1.0 /* AGC baseline decay rate (1/samp.) */
+#define MATAGCLOCK 0.2 /* AGC range (around 1) where the
+ matrix behaves passively */
+#define MATCOMPGAIN 0.37 /* Cross talk compensation gain,
+ 0.50 - 0.55 is full cancellation. */
#define CFECHODELAY 360 /* Center front echo delay (samples) */
#define CFECHOAMPL M17_0DB /* Center front echo amplitude */
More information about the MPlayer-cvslog
mailing list