H3000 Factory can operate in stereo or mono. From the user manual:
Eventide H3000 Factory is available for use on mono and stereo sources in Mono → Mono, Mono → Stereo, and Stereo → Stereo configurations. When the plug-in is in Mono input configuration the input will be routed to both LEFT and RIGHT input blocks. Similarly, when the plug-in is in Mono output mode, the LEFT and RIGHT output blocks will be summed at the plug-ins output. The plug-in also provides a dedicated input block to route side chain inputs from your DAW session into the H3000 Factory signal path.
I created a small example to demonstrate that left and right channels can interact with each other. In the attached image, input to the left channel is pitch shifted based on the envelope of input to the right channel. The result of this is sent to both the left and right outputs. I hope this helps.
-Ryerson
