I have something in a song, I don't know if it's a bug or a normal behavior:
In a SMS tune (deflemask 0.12 or 0.121), I made 3 voices + 1 with noise for the drums. The drum channel is using the 20 01 effect to make the sound. The manual says: "If it (x) is set to 1, the noise can reach any frequency at the cost of losing the third Square channel." Here x is set to zero, so it shouldn't loose the 3rd sq channel should it? Anyway, when used alone, it sounds like some kind of hi hat. But IF I enable the 3rd channel and there is something on it, then the drum sounds muffled. In the sample tune, for the 2 pattern for example, if you change SN3 to 0 or 2 instead of 1, then the drums sound again like hi hat. If I remove the notes in NS1 or SN2, it still sounds muffled.
If I convert the tune to a genesis one (moving the 4 PSG channels to the PSG channels on Genesis), then it's the same. I haven't tried on orignal hardware though (I own a genesis, but don't have any SMS). Is it a bug, or the manual is missing some informations?