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About sound in Genesis

Discussion in 'Genesis/Mega Drive' started by RedAngel, Apr 6, 2002.

  1. RedAngel

    RedAngel New Member

    Hi guys,

    I don´t understand some things about sound in Genesis.

    Genesis has two sound chips, a yamaha with 6 fm channels and a PSG with four, controlled by a z-80 processor. But there´s something about DAC channels that play samples, drumming in music etc. These DAC channels (or just channel) are in the PSG?, is it another chip or what? And could you tell me some possibilities of these chips ( sample rates and things like that)?
     
  2. Mike G

    Mike G New Member

    The DAC channel is provided by the Yamaha chip, in addition to the 6 FM channels. (Actually, I think the DAC takes the place of one of the FM channels, so you can either have 6 FM channels or 5 FM + DAC.)

    I don't really know anything about programming this chip, though. You can find the documentation at Eidolon's Inn if you're interested.

    Mike
     
  3. ExCyber

    ExCyber Staff Member

    The PSG is supposed to be a Texas Instruments SN76489-compatible, and is integrated into the VDP. IIRC it provides 3 basic frequency channels (the waveform seems to be fixed but I'm not sure what it is; probably a square wave if it's as cheap/small as it seems) plus a pseudo-random (linear feedback shift register) noise channel. I've heard that most Genesis/MD games don't actually use it, and Sega probably only put it there because:

    1) It's cheap

    2) It's needed for Mark 3/SMS compatibility

    AFAIK, the YM2610 does everything the PSG can do and more, but I'd imagine that some games use it for basic sound effects so that they don't have to "waste" a YM2610 channel that would be better for music...
     
  4. Mike G

    Mike G New Member

    Sword of Vermilion is one game I can think of that uses the PSG to good effect.

    Mike
     
  5. RedAngel

    RedAngel New Member

    Thank you.

    So if a company wanted to use all the possibilities of genesis sound in a game should know how to program well the fm channels and dac channel of the yamaha chip and also the "master system" channels of PSG.

    Many games use a bit of psg sounds and Treasure in a very good way, listen the title song of Light Crusader in Gens and deactivate fm emulation, then psg... This game uses all the channels.
     

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