SSG-EG is quite an interesting feature, and one that seems like a curious case of overengineering, yet it's also quite powerful. According to the YM2608 datasheet, it's called the "SSG-type envelope generator", essentially it's the 8 envelopes of the YM2149 PSG (derived from the 1970s General Instrument AY-3-8910) being inserted into the envelope generation step of an FM chip as an option to use instead of creating your own complex 4op envelopes from scratch. While this was likely its intent, what it actually does in PC98 and Sega Mega Drive music is far different. If you tell it to generate its envelope fast enough, like the original SSG envelope, it will introduce a characteristic sound into the signal. Basically, SSG-EG isn't just a "we pulled the shapes from SSG", no, they even accidentally copied the ability for the envelopes to go into higher frequencies. If you use a high frequency envelope on SSG while a tone is playing, it effectively causes wild amplitude modulation distortion of the wave into a C64 tripulse or 8580 sawpulse. On SSG-EG, a high pitch SSG-EG envelope will effectively amplitude modulate the operator (extended Ch3 is where this becomes evident, and it can even replace the operator if you tell the rest of the chip to make an always-on signal for that operator's usual envelope), and can produce similar types of distortion. This gets often used for better FM drums, or wilder distortion guitars. If you make the SSG-EG wave produce its saw envelope as the dominant feature of the wave, and then use the rest of the parameters to slightly change it, that's how certain SSG-EG vocals work, essentially being a sort of formant synthesis. For consonants, you can either do different types of FM noise (doable via using high feedback), or potentially SN76489, or if on OPNA, SSG noise. Also you can combine SSG-EG with extended Ch3 and Composite Sine Mode at the same time on the same channel (Ch3) to produce some seriously-wild sounds. All from features that were rarely used.
While what most of what you say is true, there are two corrections I need to make. Firstly, at one point, you say that ssg-eg can be used to modulate an always-on signal. While this is true, it's only true for the triangle waveforms. This is because the sawtooth waveforms reset the operator with each oscillation. Secondly, you cannot combine ssg-eg with CSM, at least not in the way you might think. Using CSM disables both decays of the envelope, meaning only part of ssg-eg that carries over is the change in envelope speed and quality. This means that ssg-eg allows for some more flexibility with the rates of attack and release in CSM, but that is all. Sadly, you can't have ssg-eg amplitude modulation and CSM at the same time.
That would be awesome! 😃 Honestly, Furnace is almost there. There’s a couple features in the works that would help with SSG-EG immensely, namely instrument maps (similar to sample maps). Sadly, they are pretty low priority at the moment, so it will likely be a while before they are implemented
@@SpinningSquareWaves I'm sure it'll happen eventually, this is not unlike the AY envelope and to be frank the SSG-EG is a "remnant" of that envelope system.
@@vuurniacsquarewave5091 That's true, but tuning for SSG-EG is a lot less straightforward than it is for AY. For AY, it's just one value. For SSG-EG, it's 4 values with varying effects on pitch and timbre, meaning there can be multiple correct tunings for one note, each with different timbres. That's why, personally, I'm just hoping for instrument maps, since any other solution might end up being too complicated
Thanks! It's not as bad as it used to be. I started making a big spreadsheet of different tunings I've found, which saves a lot of time. Unfortunately, the tuning doesn't carry between chips or different clock rates, so every other OPN series chip and variant needs to be tuned separately. And that's before considering the different timbres from different tunings 😵
Honestly, I would love to, but I'm not sure if I will. Game dev on its own is pretty daunting, and making games on the Genesis seems harder and less practical, by comparison. Maybe some day, but right now, that day seems distant 😔
You know, that’s not a bad idea. I might do that for a different song, but lyrics for this one are in the title. It’s just “Me and You” over and over again 😄
I'm actually playing 3 notes on FM 2, but I could have done 4. For many of the sounds in this song, I'm using an obscure feature of the OPN2 called ssg-eg. It's a bit complex in how it works, but it essentially allows me to use the operator's envelope as the source of pitch instead of the sine wave. This way, I can have 4 fully independent sounds on just one channel
I made them using an obscure part of the hardware that lets me loop each operator's envelope, called SSG-EG. There are some downsides to this, namely the difficulty in tuning with ADSR values, but it allows for a lot of really cool sounds that wouldn't be possible otherwise. This song actually uses it for a lot of different things, from the chords and the vocals, to the drums and bass.
Nope, I did it mostly by hand. The ssg-eg tuning I had done beforehand (this is for the note being sung), but specific frequencies I got for speech synthesis were initially pulled from a Wikipedia article on formant frequencies, which I then tweaked until it sounded right. I got the 'M' sound from a pdf I found talking about the formants of consonant sounds
![Me and You (Sega Genesis, YM2612 + SN76489) [Original]](/img/logo.svg){kind=logo}
