Yamaha synthesizers MSX compatible

FM-PAC has the first two:

In Pro Tracker (Tyfoon soft) they were called distorted waveforms iirc, maybe in Synthsaurus too, dunno).

In MB, direct access to these parameters was absent, though with a bit of a hack (and probably a bug) you could still tweak them low-level. Just 'wrap' the feedback around! Go from 0..7 and then forwards to 0 again, you've now changed these waveform bits. Logically, as there are two waveforms and two operators, the number of combinations equals 4, so there are 32 feedback values to check out.

Have you ever wondered why you couldn't exactly get the FM-PAC's hardware "synth" preset out of a Music Module? This is why - it uses the other waveform! Have you ever wondered why Micro Cabin's music somehow seems to eclipse FM-only music module songs? This is why; the extra waveform.

The first two waveforms are used in the FM-PAC, The capped sine being the extra/'distorted' waveform. This is a diagram of another OPL-chip, so the latter two aren't relevant here. The Music Module only has a sine as operator waveform. As these extra waveforms in the FM-PAC have a richer spectrum, their sound will be slightly richer and more complex. E.g. if you use this extra waveform for the carrier, then with the modulator you can make a sound spectrum envelope going from complex to complex, whereas the Music Module can only envelope its sound from complex to a simple sine. (not taking modulator sustain levels into account, but you get the idea)

Could it be next to the feedback parameter? Because of this quirk in MB, you're probably overwriting the waves because the feedback parameter isn't treated as a 3 bits value but as a 5 bits value..

some sources say the opll is based on the opl2, but it only used 2 waves. In the opl3 you be able to reproduce the opll sounds.

Uhm, didn't the OPL4 have 8 waveforms for each operator? If so: you can't reproduce everything the OPL2 does if it has only 4 waveforms.