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  • Joined: 01 Aug 2012
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ym2413 unknown and weird issues
Post Posted: Thu Dec 20, 2018 10:12 am
i was analising some ym2413-based vgm files, and seeing that some registers are written twice or more before a vertical blank pause (1/60 seconds, usually), which seems nonsense - and when i try to correct it (by removing those that i considered irrelevant, the previous values written to these registers), the sound sounds totally different - is that correct? what am i getting wrong from there? and what might explain such issue?
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Post Posted: Thu Dec 20, 2018 10:53 am
The key registers affect the envelope, for example a key up and down in rapid succession.
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Post Posted: Fri Dec 21, 2018 5:15 pm
the issue was related with frequencies, but affecting volume instead, and i was expecting nothing getting affected - it was on this one , https://vgmrips.net/packs/pack/namco-community-disk-magazine-2-msx-fm , 02_GameSelect.vgm
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Post Posted: Fri Dec 21, 2018 5:17 pm
i also have no idea why this one isn’t sounding anything... any idea?

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Post Posted: Fri Dec 21, 2018 7:14 pm
Can you isolate a particular write that affects the sound, and show the text dump? I can't really guess otherwise.
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Post Posted: Fri Dec 21, 2018 9:45 pm
i wonder if i could! :D - i'll try to make other experiences to try to figure out better what is going on there...
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Post Posted: Sat Dec 22, 2018 8:28 am
Those edited vgm2txt dumps are very confusing to read due to the inconsistency between the hex dump and the comments.

Anyway, you can't expect any sound of you set the volume to maximum attenuation. (the "F" in 51 31 8F)

And a minor nitpicking: You're doing the register writes in the wrong order. You usually set instrument/volume first, (register 3x) then frequency LSB (register 1x) and then you do "key on" (register 2x). (Emulation doesn't bother about it, but on real hardware doing it wrong can cause small glitches.)
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Post Posted: Sun Dec 23, 2018 12:01 am
ValleyBell wrote
Those edited vgm2txt dumps are very confusing to read due to the inconsistency between the hex dump and the comments.

the focus was on the hexdumps mainly, but i think i took some care about it


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Anyway, you can't expect any sound of you set the volume to maximum attenuation. (the "F" in 51 31 8F)

so it should be "51 31 80" instead? (let me try it... thanks!)

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And a minor nitpicking: You're doing the register writes in the wrong order. You usually set instrument/volume first, (register 3x) then frequency LSB (register 1x) and then you do "key on" (register 2x). (Emulation doesn't bother about it, but on real hardware doing it wrong can cause small glitches.)


thanks! and this about glitches is indeed important! (well, i’m a glitch-art fan, but i’m also curious about how to avoid them by default, or when neede! :D )

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