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Code Issues Releases Wiki Activity

still fiddling with surround levels

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git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@3411 b3059339-0415-0410-9bf9-f77b7e298cf2
This commit is contained in:
steve 2001-12-09 18:54:54 +00:00
parent 1351fb412a
commit 80a081bc44
1 changed files with 11 additions and 12 deletions
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23
libao2/pl_surround.c
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@ -156,19 +156,21 @@ static int play(){
out = pl_surround.databuf; in = (int16_t *)ao_plugin_data.data;
for (i=0; i<samples; i++) {
// About the .707 here and the /2 for surround:
// About volume balancing...
// Surround encoding does the following:
// Lt=L+.707*C+.707*S, Rt=R+.707*C-.707*S
// So S needs to be extracted as:
// .707*(L-R)
// But L-R could still be as much as 32767-(-32768), way off scale
// for signed 16 bits, so to avoid running out of bits, whilst still
// keeping levels in balance, we scale L and R down by 3dB (*.707),
// and scale the surround down by 6dB (.707*.707=.5)
// So S should to be extracted as:
// .707*(Lt-Rt)
// But we are splitting the S to two output channels, so we
// must take another 3dB off as we split it:
// Ls=Rs=.707*.707*(Lt-Rt)
// = .5*(Lt-Rt)
// This result is handy as it is also sure not to clip, even
// though L could be full scale +ve, R full scale -ve
// front left and right
out[0] = in[0]*.707;
out[1] = in[1]*.707;
out[0] = in[0];
out[1] = in[1];
// surround - from 15msec ago
out[2] = pl_surround.delaybuf[pl_surround.delaybuf_ptr];
out[3] = -out[2];
@ -184,6 +186,3 @@ static int play(){
ao_plugin_data.len=samples*sizeof(int16_t)*4;
return 1;
}