A map of connections between musical features and musical expression have been much sought-after. Unveiling a system behind the musical expression humans achieve and perceive intuitively could benefit a range of human activities including musical composition, therapy, and computer science. The present study featured an experiment in which 50 participants rated the expression of valence on a 9-point scale after listening to 10 music samples. The only difference between the samples was the pitch of one note (occurring at various times, octaves and instruments). Each condition featured the note as forming a different interval in regard to the tonic (the first scale degree, and the tonal focal point). The intervals were: minor second, major second, minor third, major third, augmented fourth (the tritone), perfect fifth, minor sixth, major sixth, minor seventh and major seventh. Participants also rated their musical sophistication by answering the 40 questions of the Gold-MSI self-report inventory and a resulting index variable ranging from 40 to 120 was obtained. Statistically significant finds were made and a pattern emerged where minor/augmented intervals code for negative valence and major/perfect intervals code for positive valence. The expression of the minor and major sevenths appeared neutral, but results lacked statistical significance. The musical sophistication of participant was associated with the ability to perceive musical expression of affect. Finally, the term intervallic semiosis was proposed as a designation for the explained functionality of valence coding.