Yeah, the whistle was unmistakable. I heard it (in live, real time) and I was in a pub.
I love UCL semi-final stage, for me it's even more dramatic than the final. It's an odd bit of sport when the championship game is somehow less dramatic - but it is! The final is on a neutral site, on a Saturday.
The semis have both legs, in front of rabid home supporters - on a weeknight and the result is after 180 minutes plus time. It's just cooler.