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improve apu pulse channel nonlinear mixing precision #89

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improve apu pulse channel nonlinear mixing precision #89

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245f03a
improve apu pulse channels non-linear mixing precision
tsone Jan 24, 2025
fbe2e21
change square_table lookup generation use (1<<17)
tsone Feb 4, 2025
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23 changes: 11 additions & 12 deletions xgm/devices/Sound/nes_apu.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -147,19 +147,18 @@ namespace xgm

if(option[OPT_NONLINEAR_MIXER])
{
INT32 voltage = square_table[out[0] + out[1]];
m[0] = out[0] << 6;
m[1] = out[1] << 6;
INT32 ref = m[0] + m[1];
INT32 ref = out[0] + out[1];
if (ref > 0)
{
m[0] = (m[0] * voltage) / ref;
m[1] = (m[1] * voltage) / ref;
INT32 voltage = square_table[ref];
m[0] = (out[0] * voltage) / ref;
m[1] = (out[1] * voltage) / ref;
}
else
{
m[0] = voltage;
m[1] = voltage;
// square_table[0] = 0;
m[0] = 0;
m[1] = 0;
}
}
else
Expand All @@ -170,11 +169,11 @@ namespace xgm

b[0] = m[0] * sm[0][0];
b[0] += m[1] * sm[0][1];
b[0] >>= 7;
b[0] >>= 11;

b[1] = m[0] * sm[1][0];
b[1] += m[1] * sm[1][1];
b[1] >>= 7;
b[1] >>= 11;

return 2;
}
Expand All @@ -190,8 +189,8 @@ namespace xgm
option[OPT_NEGATE_SWEEP_INIT] = false;

square_table[0] = 0;
for(int i=1;i<32;i++)
square_table[i]=(INT32)((8192.0*95.88)/(8128.0/i+100));
for(int i=1;i<32;i++)
square_table[i]=(INT32)round(((1<<17)*95.88)/(8128.0/i+100));

square_linear = square_table[15]; // match linear scale to one full volume square of nonlinear

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