The phrase "untrained ear" means that someone is not experienced or knowledgeable in listening or understanding certain sounds or aspects of music or other sounds. Full definition
To my admittedly untrained ear, what he seems to be saying is that poverty does matter and some kids are more prepared to learn than other kids. (norinrad10.com)
In his scrupulous hands, the disputing voices of the Talmudic house of study, however cacophonous to the untrained ear, revealed their multiple strands of meaning and invited his students to become participants in this dialogue of the generations. (firstthings.com)