According to Prof. Erik Nakhjavani in Encyclopædia Iranica: "Analogous to Delkash, before her, Hayedeh sang with technical authority and passionate energy. Her laryngeal control made it possible for her to produce a series of graceful vibrato and glissando vocalizations required by the Avaz Persian vocal music. She could smoothly pass from the upper reaches of her alto voice to the lower, fuller, and darker range of the contralto. This mixture of strong laryngeal strength and learned vocal technique gave her alto-contralto voice a rare, powerful resonance and texture in the performance of the Avaz. Furthermore an acute sense for musical timing, the rhythmic flow of vocal music, affective musical phrasing, and poetic delivery enabled her to express and interpret effectively any songs she sang."
