This is a two input / two output DC-coupled mixer with input level controls. The inputs are pre-patched to the LFO triangle wave and to the ENVELOPE GENERATOR 1, but can be coupled to any other source.
The outputs deliver the sum of the attenuated input signals and its inverted signal (sum+ and sum-). These outputs are pre-patched to the PWM inputs of OSC1 and 2 (see above). Especially when using the LFO signal,
this can be a useful choice since the mixers outs provide the LFO signal with opposite polarity to OSC1's PWM respective OSC2's PWM. Consequently, the oscillators pulse width sweeps in opposite directions which results in interesting sonic possibilities.