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Fix screeching in regulus: When summing together four equal channels, the size of the max amplitude per channel should be 1/4 of the max range, not 1/3. oops. No idea when this bug is from, but its OLD.

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This commit is contained in:
Jonathan Gevaryahu 2009-11-16 05:58:42 +00:00
parent 65dc27ae95
commit a04f60c0f4
1 changed files with 7 additions and 2 deletions
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9
src/emu/sound/sn76496.c
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@ -5,7 +5,7 @@
Routines to emulate the:
Texas Instruments SN76489, SN76489A, SN76494/SN76496
( Also known as, or at least compatible with, the TMS9919.)
( Also known as, or at least compatible with, the TMS9919 and SN94624.)
and the Sega 'PSG' used on the Master System, Game Gear, and Megadrive/Genesis
This chip is known as the Programmable Sound Generator, or PSG, and is a 4
channel sound generator, with three squarewave channels and a noise/arbitrary
@ -48,6 +48,11 @@
14/11/2009 : Lord Nightmare
Removed STEP mess, vastly simplifying the code. Made output bipolar rather
than always above the 0 line, but disabled that code due to pending issues.
16/11/2009 : Lord Nightmare
Fix screeching in regulus: When summing together four equal channels, the
size of the max amplitude per channel should be 1/4 of the max range, not
1/3.
TODO: * Implement a function for setting stereo regs for the game gear.
Requires making the core support both mono and stereo, and have
@ -270,7 +275,7 @@ static void SN76496_set_gain(sn76496_state *R,int gain)
gain &= 0xff;
/* increase max output basing on gain (0.2 dB per step) */
out = MAX_OUTPUT / 3;
out = MAX_OUTPUT / 4; // four channels, each gets 1/4 of the total range
while (gain-- > 0)
out *= 1.023292992; /* = (10 ^ (0.2/20)) */