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Thread: Does anybody understand how OPL2 percussion mode works?

  1. #1
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    Default Does anybody understand how OPL2 percussion mode works?

    Been trying to tweak the OPL2 (adlib) drum sound for my game in progress and ran into some trouble. I thought the snare drum sounded too much like the hihat so I tried playing with some registers but no luck, ADSR envelopes were really straightforward once you figure out which registers correspond to each drum (this is not very well documented), but I could clearly tell that something was still missing cause I couldn't get a good sound.

    At this point I figured that I should try using DosBox to dump the registers from a decent drum sound then just copy the settings so I fired up Adlib JukeBox and grabbed the settings. This method showed me that I had neglected to set the Frequency registers for the drums, which I didn't know actually made a difference. So I copied all the registers from Adlib JukeBox that I thought would affect the drums but no luck, my drums don't sound the same, in fact they sound horrible. I think I'm missing some really important register setting but I can't find much documentation on the percussion mode.

    So far I've messed with the 0x20, 0x23, 0x40, 0x43, 0x60, 0x63, 0x80, 0x83, 0xE0, 0xE3, 0xC0 registers for each drum channel and the Pitch/Fnum registers. Does anyone know any other registers which affect the drums?
    Last edited by PgrAm; October 7th, 2017 at 08:59 AM.
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  2. #2

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    Yeah, it's very poorly documented. ModdingWiki has a teensy bit more information, but not much. I suppose one method would be to poke through the source of an OPL2 emulator and see if it can be determined that way.

    I'm kind of curious if the feedback parameter affects the drum sounds that take over "modulator" operators, and/or if that's part of how the "noise" sounds are generated.
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  3. #3
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    Thanks, I looked at the ModdingWiki article but unfortunately there's nothing new I could find. Ill do some experiments on the feedback parameters and keep you posted.
    Currently working on new DOS game, Chuck Jones: Space Cop of the Future, Check out my Dev Blog. WARNING: contains rocket powered El Caminos

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  4. #4

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    A while back I was using an online tool to control the chip ( years ago ). The problem was it wasn't doing all it was suppose to. I ended up writing directly to the ports as it wasn't doing what it said it was doing.
    Dwight

  5. #5

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    Quote Originally Posted by PgrAm View Post
    I thought the snare drum sounded too much like the hihat
    It's yamaha FM in single operator mode -- the BASS DRUM usually sounds like a hihat too, USUALLY not a lot you can do about that. I've never heard anything done in percussion mode on OPL that didn't sound like a bunch of tin cans being banged by monkeys with soda straws.

    But to be fair, to my ears even "The Fatman's" legendary FM tracks make me want to heat up 12" long sewing needles in my gas forge and jam them into my ears. I'm the nutter who thinks even CMS sounds better as it least it doesn't TRY to be something it's not.

    THAT SAID I think I have working code for that here somewhere, I'll dig and double check. Worst comes to worst, I have that Blaster Guide book that documents damned near everything.
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  6. #6
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    Most software outside of Adlib's own didn't really use percussion mode, so don't feel obligated to use it. Yes, it gives you 2 additional voices, but the loss of flexibility is usually too high a penalty.
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  7. #7

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    Quote Originally Posted by Trixter View Post
    Yes, it gives you 2 additional voices
    Which I never understood why it wasn't 3 voices since you're losing three two-operator for one-operator... or is that extra missing channel applied to all five rhythm voices?
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  8. #8

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    Demo of an Adlib clone with an OPL2 in rhythm mode -- don't miss "ACTION3" at the end:

    https://www.youtube.com/watch?v=6JuXXRAHios&t=2m36s

  9. #9

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    Quote Originally Posted by deathshadow View Post
    Which I never understood why it wasn't 3 voices since you're losing three two-operator for one-operator... or is that extra missing channel applied to all five rhythm voices?
    One of the five percussion sounds (I think the bass drum?) uses two operators; the other four use one.
    Computers: Amiga 1200, DEC VAXStation 4000/60, DEC MicroPDP-11/73
    Synthesizers: Roland JX-10/SH-09/HS-80/MT-32/D-50, Yamaha DX7-II/V50/TX7/TG33/FB-01, Korg MS-20 Mini/ARP Odyssey/DW-8000/M1, Ensoniq SQ-80, E-mu Emax HD/Proteus-2, Casio CZ-5000, Moog Satellite, Sequential Circuits Prophet-600
    "'Legacy code' often differs from its suggested alternative by actually working and scaling." - Bjarne Stroustrup

  10. #10

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    For an out-of-the-box approach, you can play digitized drums on the SB interface, and use OPL2/3 for the rest of the music. Zone 66 did this. Won't work on actual Adlib cards of course, but most people have something SB compatible.

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