Talk:OPL emulation


This page could do with some serious improvement IMO. It seems like it's mostly a general discussion of OPL synthesis and emulation, when it ought to be focused on how it relates to Doom in particular. For example, Vanilla Doom only supports the OPL2 (and OPL3 to a limited extent if you set the right flag), so discussing other, later OPL chips is kind of irrelevant.

The other thing that is completely missing here is any discussion of the front end MIDI part of the OPL synthesis. In writing Chocolate Doom's OPL code, this was actually the biggest challenge, and just as essential to achieving OPL MIDI playback that matches Vanilla as having a good emulator is.

It's worth noting that perfect OPL playback is indeed plausible in theory, albeit complicated and difficult to achieve. Check out where they have a complete reverse engineered 6502 CPU core based on decapped 6502 chips scanned at high resolution. Theoretically the same could be done for the OPL2 - it can be reasonably assumed the chip is nowhere near as complicated as a full CPU is. Fraggle (talk) 18:03, 30 July 2014 (UTC)

You're probably the best qualified to address these points, frankly. I barely know anything about OPL. While we're on the subject of emulation, however, I've heard in the past that one particular challenge toward getting an authentic sound lies in the presence custom DACs on AdLib cards which sit between the synth chip and the audio output. Any comment on that? Should it be mentioned in the article? --Quasar (talk) 20:15, 30 July 2014 (UTC)
Certainly there are all kinds of things that can have an effect, from the DAC to the analog circuitry on the sound card, to the speakers you're using. I remember when I implemented PC speaker emulation, I wondered if I should try to emulate the deafening from the plastic of the PC case :)
The YM3812 (OPL2) has a standard DAC that you're supposed to use with it (wikipedia:YM3014B). I don't know how much of an effect that has; there might be oddities about how it works but I don't know much about it. The OPL3 has a partner DAC chip of its own (YAC512). In general I would be surprised if the DAC has that big an effect on the sound compared to things like the board circuitry etc. Fraggle (talk) 20:40, 1 August 2014 (UTC)