Op-1 + Ipad Garageband : audio feedback (larsen)

Hello guys,

I was watching this video :

I wanted to do the same thing :
Send the midi data to the iPad, and then recording the audio form the iPad back into the OP-1.
I guess that's how he did it.

But I get a very noisy audio feedback.
Do you have any idea ?

I think the author of this video is on this forum.

Thanks for your help !