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restates the notes about the error in LFO table as listed in the original manual for the ymf271.

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Also include Nicola's version of the formula
This commit is contained in:
Brian Troha 2009-11-01 03:34:24 +00:00
parent 5ecfb2044b
commit 48f5d42b1b
1 changed files with 20 additions and 15 deletions
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35
src/emu/sound/ymf271.c
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@ -160,26 +160,31 @@ static const double DCTime[] =
/* Notes about the LFO Frequency Table below;
There appears to be at least 2 errors in the table from the original manual.
There are 2 known errors in the LFO table listed in the original manual.
Both 201 & 202 where listed as 3.74490. 202 has be changed to 3.91513 which was computed based on formulas by OG & Nicola
232 was listed as 13.35547. We use 14.35547 as this is the correct value based on the formula listed below:
Both 201 & 202 were listed as 3.74490. 202 has be corrected to 3.91513
232 was listed as 13.35547 but has been replace with 14.35547.
Corrections are computed values based on formulas by Olivier Galibert & Nicola Salmoria listed below:
LFO period seems easy to compute:
int lfo_period(int entry)
{
int ma, ex;
entry = 256-entry;
ma = entry & 15;
ex = entry >> 4;
if(ex)
return (ma | 16) << (ex+6);
else
return ma << 7;
}
Olivier Galibert's version Nicola Salmoria's version
lfo_freq = 44100 / lfo_period
int lfo_period(int entry) or int calc_lfo_period(int entry)
{ {
int ma, ex; entry = 256 - entry;
entry = 256-entry;
ma = entry & 15; if (entry < 16)
{
ex = entry >> 4; return (entry & 0x0f) << 7;
if(ex) }
return (ma | 16) << (ex+6); else
else {
return ma << 7; int shift = 6 + (entry >> 4);
} return (0x10 + (entry & 0x0f)) << shift;
}
lfo_freq = 44100 / lfo_period }
*/