Is there really a standard american accent. Are you referring to newsreaders on TV and commentators etc, much like RP(received pronunciation) on BBC is considered standard British. Isn't the way one speaks in America largely dictated by education, region ( and variation even within states/regions), subculture ( inner city, etc). A good idea would be to read the book "do you speak american" ( available for $5 used on amazon) to appreciate the wide variety of spoken english in the USA ( the book staes canada is more uniform for native speakers, except for the maritimes, esp newfoundland). What the book states is also affirmed by my own experience in interracting with people from different regions and social backgrounds.