The Mixer section combines signals prior to the filter section.
Oscillator I/Oscillator II level- Sets the amplitude of each oscillator. Unlike most analog synths, these can really make a difference in the overall sound, particularly in conjunction with the filter Resonance, Filter Drive, and Starve controls and the Amp section Amp Drive control. We definitely recommend experimenting with oscillator levels if you're getting out there the aforementioned filter and amp controls!
Noise - Sets the volume level of Atomika's white noise generator. For those of you hoisting clipboards, white noise is a random signal wherein all frequencies across the frequency spectrum are represented equally (and for those of you who aren't... it's a loud hissing sound).