Hearing the vibration of Hare Krishna automatically reminds one of Krishna’s Pastimes. So both of them arise simultaneously in the mind when one is sincerely chanting. So you cannot make any distinction between listening to the sound and thinking of the Pastimes. But the process is to hear, and then Krishna’s Pastimes, Form, Qualities, etc. will automatically come to mind.

From Srila Prabhupada’s letter to Satsvarupa — New York 10 April, 1969