Tune/improve channel gain/drive balancing

[mbitsnbites]

Idea:

• Change scale of osc/noise volume so that max is much more than 1.0.
• Always limit to [-1, +1] in the dist step, even if dist == 0.
• Rebrand the "drive" paramater to "channel volume" (which it already is, in fact), and possibly raise the max channel volume.
• See if the distortion step can be made louder for high distortion factors.