M1

M1, or Mechanism 1, describes the laryngeal configuration commonly called chest voice or modal register. In this state, the thyroarytenoid (TA) muscle maintains significant activation, keeping the vocal folds shorter and thicker. The body-cover relationship produces a vibratory pattern with substantial vertical phase difference and longer closed quotient (Titze, 1994).

Acoustic characteristics of M1 include stronger fundamental frequency and lower harmonics, producing the ‘richer’ quality associated with chest voice. The H1-H2 relationship (difference between first and second harmonics) tends toward negative values, indicating extended closed phase (Titze, 1994).

Maintaining M1 coordination while ascending in pitch requires increasing CT activation to raise pitch while maintaining sufficient TA engagement to preserve the characteristic thick-fold vibration pattern. When singers rely on excessive subglottic pressure, raised larynx, or wide pharyngeal tension to maintain M1 quality, it indicates compensation for inadequate intrinsic muscle coordination.

The transition from M1 to M2 (the passaggio) involves a shift in the TA/CT balance. Titze (2014) demonstrated this can be understood as a bi-stable phenomenon, where small changes in glottal geometry near the transition point produce large changes in aerodynamic driving pressure, causing the characteristic ‘break’ when poorly managed.