SCC: high frequency notes do not sound correctly

[toyoshim]

High frequency notes do not seem to sound correctly.
E.g. SpaceManbow's 1st stage BGM has a melody like "D- C#- BGA-", and there the last three notes, "BGA" do not make any sound. Register values are 0x0038, 0x0046, and 0x003f for each.

[Kyuchumimo]

I found that values below 0x004f (F5) do not sound correctly, so that the supported values are from 0x0fff (G#-1) to 0x004f (F5).