I wanted to see if it was possible to create a side-chain pump effect on an OP-1. I've tried a bunch of things in the past and this seems like the most practical method. It can work with several of the synth engines, but for the sake of this example, I'll use DRWAVE because it can easily achieve a very full, synthpad sound.
To start with a neutral sound, Shift + (1) takes you to the Engine selection menu. This is the screen that doesn't give you the option for the premade patches. Note: This menu will allow you to keep the settings that you programmed for the Envelope, FX & LFO, and try it with different engines.
After pressing Shift + (1), switch to DRWAVE. The default setting is great, except for the sweeping modulation, so turn the orange encoder counter-clockwise until it stops. I think the tone is most pleasant when the octave is set to 0 or 1.
Press (2) + Shift. Make sure that the Playmode is set to POLY. The Portamento isn't necessary for this effect.
I attached a photo of the ideal envelope setting. The perspective is a bit shifted because of my phone's angle, you will actually want that faint vertical line to align with the space between buttons 1 & 2. The envelope is really the most important part of the effect. With the white encoder, bring the sustain all the way down. Turn the orange encoder clockwise to decrease the amount of release.
Go to the ENDLESS Sequencer and enter your chord progression. Set it for 1/4 and you should only have a single dot for the pattern.
Let the sequence play and that's it! You can return to the envelope screen and play around with the green, white & orange encoders to get variations on the effect.
If you try this, feel free to post your examples below or anything else that you discover.