This manuscript sought to investigate rater cognition by exploring rater types based upon differential severity and leniency associated with rating scale items, rating scale category functioning, and dimensions of music performance assessment. The purpose of this study was to empirically identify typologies of operational raters based upon systematic differential severity indices in the context of large ensemble music performance assessment. A rater cognition information-processing model was explored based upon two frameworks: a framework for scoring and a framework for audition. Rater scoring behavior was examined using a framework for scoring, where raters’ mental processes compare auditory images to the scoring criteria used to generate a scoring decision. The scoring decisions were evaluated using the Multifaceted Rasch Partial Credit Measurement Model. A rater typology was then examined under the framework of audition, where similar schemata were defined through raters’ clustering of differential severity indices related to items and compared across performance dimensions. The results provided three distinct rater-types: (a) the syntactical rater; (b) the expressive rater; and (c) the mental representation rater. Implications for fairness and precision in the assessment process are discussed as well as considerations for validity of scoring processes.