Hi, In GENS- you can disable four options under 'audio'. z80 YM2612 PSG DAC. I know the first two are processors- with the YM being the dedicated Yamaha and the Z80 being teh Zilog chip. What are the PSG and DAC? Did all games use each of these in their music generation? What are the sound characteristics of each? Mega Drive sound generally sounded very 'metallic', and I believe that is the Yamaha chip- what is the reason for this characteristic? Some MD games have awful music. Otheres (Eg Sonic) have stunning music. Does the better music use the chips in unison better than bad music? Is it hard to program them in 'sync'. Just very interested in this entire field. Any information or links would be most appreciated. It is so interesting fiddling with these options in GENS. In Sonic 3D, disabling the YM removes the melody. Disabling the Z80 seems to kill it- the timing becomes off and so does the pitch (is this to do with this...? [wiki] The sixth channel can act as a surrogate PCM channel by means of the 'DAC Enable' register, allowing the chip to play 8-bit PCM sound samples. Enabling the register disables FM output for that channel. PCM data is written to the channel via an 8-bit register. The YM2612 does not provide any timing or buffering of the PCM samples, so all frequency control and buffering must be done in software by the host processor.) Disabling the DAC kills everything, whilist leaving the DAC and Z80 on just leaves the drum sounds. And sound effects all seem to be generated by the YM. In Talespin- with dreadful muisc- disabling DAC just removes a drum sample, and the music plays. The YM is doing all the 'melody'. And the PSG does nothing. Arg- I'm just craving more info and how these components were used.
PSG = Programmable Sound Generator DAC = Digital to Analogue Converter (used especially for drum things).
The PSG is (originally) an SN76489 Soundchip. Thats the one you have in the Master System. You will hear it only when playing MS Games afaik not a single MD Games uses the YM2612 and the PSG together, although It would possible (iirc the BIOS does this). The 'metallic' Sound is coming from the YM. It is making sounds using FM Synthesis (FM), and 'metallic' often is a fitting description of what you can do with it It looks like in GENS the sound is taking this way: Z80 -> PSG + YM2612 (sound synths) -> DAC (plays Samples and mixes them with the synthesized sounds) -> Output (speakers) So disable the YM2612 and all you can hear are the samples. Disable the DAC and you hear nothing, etc. . In reality, the PCM Sample is played by the YM2612 aswell, but maybe its easier to work with the chips like this? I dont know. The DAC only transforms the digital signal (from PSG+YM) into an analog signal, which you can feed into your Speakers then. It does not "play" anything at all, but it is essential if you want to hear something.
FM synthesis. It's a complex method of sound generation that is not intuitive and requires a reasonably high level of mathematical and programming competence from the composer. Since most composers aren't programmers and vice versa this presents something of a problem. It's the reason some MD games have truly terrible music - it's a tough chip to work and it takes time to become competent with FM synthesis. By contrast the SNES had a separate sound board with a wavetable synth (sample-based, had its own dedicated CPU and RAM) and software conversion utilities for MIDI, all of which sounds a lot more friendly. I don't really understand why the DAC is listed in GENS. I suppose its audio characteristics are being emulated? I also don't understand how Tailspin can play any music at all if it's disabled, it's obviously essential for any sound to be played. 0s and 1s need to become waveforms before they can be heard! The YM chip isn't classed as a CPU, incidentally.
here some very nice (& bit more wealthy) later 80s FM examples: http://www.youtube.com/watch?v=Fzs72z-9Je0&fmt=18 http://www.youtube.com/watch?v=Z7u5gVyluBc&fmt=18 http://www.youtube.com/watch?v=yEQdUPcu_j0&fmt=18 http://www.youtube.com/watch?v=gABVCOStUDo&fmt=18
This is not true and in fact hundreds of games use the YM2612 and SN764** PSG chips together. (Also, MDs from 1988-1991 have no BIOS and thus the BIOS plays no part in setting up audio. It's a lockout chip for unlicensed games.) Turn off the YM chip in your player's options and try game soundtracks like Gauntlet IV, Sonic, Streets of Rage, Gunstar Heroes, etc. You'll hear the PSG used for backup melodies and some leads. Gunstar Heroes is in fact very PSG-heavy. Anyway, the Z80 CPU is often used as the sound driver in most MD games, because it's otherwise left idle with the 68K CPU running the game itself.
T.M.N.T. The Hyperstone Heist uses the YM2612, PSG, and DAC together very well. When I read this I checked out some other games, like Castlevania Bloodlines which seemed to me to only use the YM2612. It didn't seem to use the PSG or DAC at all, atleast not in the brief bit I played with the others disabled.
The DAC only handles digital samples, usually output under control of the Z80. The 2612 synth and PSG do not go through the DAC for output.
