Many games report 6 channel output while only providing data for 2. We only output 2-channel audio regardless, and in the downmixing, front left/right only provide 36% of their volume. This is done assuming all of the other channels also contain valid data, but in many games they don't. This PR alters the downmixing to preserve front left/right, so volume is not lost.
This improves volume in Link's Awakening, New Super Mario Bros U, Disgaea 6, Super Kirby Clash.
While were at it, we can also enable sign conversion warnings and other
common warnings as errors to prevent these from creeping back into the
codebase.
In a lot of cases, we can make use of const references rather than
non-const references.
While we're in the area we can silence some truncation and sign
conversion warnings.
Kelebek1