removing echo

[chkil]

Since you have 2 tracks out of sink I had an 'Idea':

1. Remove one of the tracks , either left or right.
2. Use noise reduction to mute/remove all or most of the main dialogue, keeping the echo "at the same original volume".
3. Duplicate and invert track to remove the echo.

The best case is that the main audio volume will drop significantly but you could probably boost overal track volume back up to normal levels and the echo would basically be gone.

I am also looking into removing echo from a lecture.