Sound Issues in Valis I

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What steps will reproduce the problem?
1.Load Valis I rom
2.Hold down A+B+C at the title screen and hit START to access the sound test
3.Listen to the music, especially track 5 "Lonely Soldier" and track 6 
"Cellular Tissue"

What is the expected output? What do you see instead?
There is a audible popping sound that isn't heard in Kega. Unfortuantely I 
cannot test this on actual hardware.

What version of the emulator are you using (official, SVN revision,...)?
Libretro version compiled from the latest source (equivalent to 1.7.3 I believe)

Please provide any additional information below (Emulator settings, Console
setting,...)
Enabling or disabling PSG noise boost or lp filter had no effect on the popping 
sound

Original issue reported on code.google.com by michaels...@gmail.com on 1 Dec 2012 at 9:43

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i just tested the entire siundtrack (some really nice tunes i must say) on my 
MD2 with Genesis Plus GX running aside on my Wii (same TV) and there wasn't any 
difference, it's actually very accurate.

there is indeed a slight repeating sound in the background in track 5 and 7 but 
i am not sure what you exactly meant by popping sound (hard to tell without a 
recording)

anyway, there is nothing wrong with genesis plus gx core and either kega is 
wrong or the libretro port did something wrong

ps: enabling low pass filter also helps getting more accurate (i.e muffled) 
sound, the sound of my md2 is less clear than emu

Original comment by ekeeke31@gmail.com on 2 Dec 2012 at 2:10

• Changed state: Invalid

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in this game, especially in the fifth tune, rhythmic sounds is heard with some 
chunk-sound, it sounds like very fast volume attack.
it can be heared on almost all emulators - GenesisPlusGX, Regen, MESS, Gens 
clones, but not present on Kega - there are flat sound without that "pops"

Original comment by 0vet...@gmail.com on 2 Dec 2012 at 4:35

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Like i said, i compared the sound in genplus-gx with the real console 
simultaneously on the same tv and it sounded exactly the same.

Those "pops" like you call them are definitively there on real hardware too 
and, even if it sounds better in Kega (indead perfectly clear sound on this 
track), it does NOT sound like that on my MD2, and it's not because of the 
usual distorsion or something like that, those are sound produced by the chip ( 
not sure but it could be related to the DAC channel rather than real instrument)

Original comment by ekeeke31@gmail.com on 2 Dec 2012 at 5:05

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i actually just confirmed that this is related to channel 6 in DAC mode, 
disabling DAC output in genplus-gx actually make those pops disappear.

not sure what Kega is doing but it is not accurate

Original comment by ekeeke31@gmail.com on 2 Dec 2012 at 5:12

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"not sure what Kega is doing but it is not accurate"
what was the goal of my message :), you probably missunderstood me, I didn't 
mean something wrong in GenPlus, but instead Kega probably have some hacks to 
make "better sound", not like on original hardware

Original comment by 0vet...@gmail.com on 2 Dec 2012 at 5:29