Is Deco true stereo?

Yes, Deco is true stereo except in Wide Stereo and Bounce modes. It has a single TRS input jack that can receive two TS connections when using a TRS stereo adapter.

In Bounce mode, the right channel of the Lag Deck is phase-inverted and bounced to the LEFT channel input, resulting in a ping-pong-like stereo effect.

When in Wide Stereo mode, the WET signal is summed to mono and sent to both the Reference Deck at the LEFT OUT and the Lag Deck on the RIGHT OUT.