Imtiaz, Irshad's contribution immense in my career: Ranbir

"I have worked with Irshad in two other films, besides 'Rockstar' so I have a deep association with him. When I heard the songs of 'Rockstar', especially 'Jo Bhi Mai...', it gives you a sense of the gaps you feel as an actor, that you know are hard to fill in through a performance, Irshad fills those with his words and it makes your character more believable," he said.