My guess is that a little bit of old-fashioned manual reading will illuminate:
"The left input (channel #1) or an internal noise source feeds carrier (instrument), while right input (channel #2) feeds the modulator (voice). The output is the sum of ten frequency bands from 20Hz to 20kHz, with 'level' and 'pan' for each band."
This means that you should connect your mic or guitar to channel #2, and then either use the noise source or some wideband signal on channel #1. Then you should get a result.
