The present study aims to comparatively examine the concept of musical expressivity in Western classical music and “Bayān-e Hāl” in Iranian Dastgāh music and to explain how this comparison can contribute to formulating an indigenous framework for documenting the expressive components of performance. In this study, aesthetic perspectives on Islamic art—particularly the relationships between form and meaning, outward appearance and inward reality, and the inner experience of the artwork—serve as the theoretical framework for interpreting expressive qualities in Iranian music. The research is applied in purpose and qualitative in approach, employing descriptive–analytical and comparative methods. Data were collected through the study of theoretical and musicological sources, examination of selected examples from the Dastgāh repertoire and performance practices, and interviews with 12 Iranian musicians and instructors, and were analyzed qualitatively. The findings indicate that in Western music, a substantial part of expressive quality is documented through signs such as dynamics, agogics, and articulation, whereas in Iranian music, Bayān-e Hāl is realized less through a fixed system of written signs than through the interaction of modal structure, improvisation, performance experience, and performers’ moment-to-moment decisions. The study concludes that a two-layer model comprising “intent” and “performance” can provide more precise possibilities for documentation, analysis, pedagogy, and preservation of expressive components while maintaining the fluid and improvisatory nature of Iranian music.