Mega Drive: The Pulse 3 comment
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The article says that the pulse 3 channel was unused in the Green Hill example due to gameplay reserving it for sound effects. However, it's unused because the noise channel is using pulse 3's frequency.
I'm still refreshing my recollection about the SN76489 and I remember the frequency of pulse 3 affected the noise channel in 'periodic' mode. Is this the case for Green Hill though? I'm just wondering because I don't see anything special happening with the noise channel in the case of green hill, as far as I understand.
It indeed does use it for all of the tracks in Sonic 1. For example: https://github.com/cvghivebrain/s1disasm/blob/main/sound/music/GHZ.s#L467
The driver does technically allow the other modes for noise, but the game specifically chooses to use the PSG3 mode instead, probably to get a specific kind of sound out of it that can't be done with the other modes.
Corrected, thanks