I do this ALL the time! Even though I can see the channel fader is down/crossfader is on the other side (and I always keep my finger on the side of it to make sure it doesn't move when I'm cueing a song) I still take the headphones off and check, just in case!!
I did have it once where I had accidentally moved one of the crossfader assign switches on the front of my MC6000, I was cueing away and the whole crowd could hear it! Wasn't until I noticed that they were giving me dodgy looks that I realised!
Bookmarks