Hxx (HF9) makes different sounds on the two 2A03 Pulse Channels

[LunuLeaf]

Hello,

at first I am not sure if there is an existing topic of this, but I found out, that the Hxx-effect makes different sounds in the 2 2A03 Pulse/Square Channels (specifies if you type in "HF9").

I made an example where you can see the differences in the sound between the channels, althought both channels have the same pattern.
I also tested this in FT (0.5) and OCC (0.3.14.5), and in both this bug appears.

[MovieMovies1]

This is not a bug. The hardware sweep units act slightly different between the two channels.

[LunuLeaf]

Oh, I didn't know about that and just thought it would be a bug. Sorry about that.

[Xyz]

Well it is a bug, just a hardware bug rather than FT's fault.

[PinoBatch]

In other words, FamiTracker is being bug-for-bug compatible with the known (mis)behavior of the APU sweep unit, as described on NESdev Wiki:

The two pulse channels have their adders' carry inputs wired differently, which produces different results when each channel's change amount is made negative.