John Petrucci was asked by Rick Beato about his headphone mix during Dream Theater gigs, to which he replied (transcribed by UG):
"My headphone mix is unbelievable.
"It sounds like the CD mix I guess, but the guitar is just slightly higher above. I can hear everything unbelievably clear, it's really powerful.
"And here's the shocker - I have no vocals in my mix. So, it's like an instrumental Dream Theater mix with the guitar louder.
"And the reason I don't have vocals is not because I don't love the way that James [LaBrie] sings, it's that he is walking around stage with a live microphone.
"Wherever he goes it's gonna pick up the drums, the audience, whatever...
"When that mic is open, all this additional ambience [gets in the mix]. When you shut that off, it closes up. It's like studio - that's the reason I do that, I want this big defined sound.
"And it just sounds so heavy and so good. I wish everybody could listen to my mix. I wish I could hand it out to the audience. It's really a great sound."