On my original Columbia LP and '80's CD reissue of Miles Davis - "Milestones" there is that slapback echo which was added to the entire mono mix. Was this originally intended and added by producer, Teo Macero, or done after-the-fact by Columbia engineers? All subsequent remasters (Japanese mono and Sony stereo remix) have no echo at all. I personally like the echo - it adds a "coolness" to it! Plus it's the version that I grew up on.