Phonation Threshold Pressure – Voice Science

Phonatory threshold pressure (PTP) is the minimum lung (subglottal) pressure required to initiate self-sustained oscillation of the True Vocal Folds. In healthy adults at comfortable pitch, PTP typically measures 2–5 cm H₂O (0.2–0.5 kPa). Because PTP directly reflects vocal fold tissue properties—stiffness, viscosity, and geometry—it serves as a clinical and research measure for assessing vocal fold health, detecting pathology, and monitoring treatment outcomes.

Context

Relevance to Singing

For singers, phonatory threshold pressure represents a fundamental measure of vocal efficiency. Lower PTP indicates that less respiratory effort is required to initiate phonation—correlating directly with pedagogical concepts of “ease of phonation” and “vocal freedom.” Conversely, elevated PTP signals increased tissue stiffness, dehydration, or fatigue, requiring greater driving pressure that singers often perceive as effortful or strained.

PTP increases exponentially at high pitches while remaining relatively stable across low-to-moderate frequencies, explaining why singers experience greater effort demands in the upper range. Research consistently shows that trained singers maintain stable PTP after extended loud vocalization, while untrained voices show significant elevation—demonstrating the protective vocal efficiency gained through training (Enflo, Sundberg, and McAllister, 2013). Hydration profoundly affects PTP: exposure to dry air for just five minutes significantly increases threshold pressure, while adequate systemic and surface hydration maintains optimal tissue pliability for efficient oscillation.

Historical Discovery and Development

The theoretical foundation for PTP emerged from van den Berg’s 1958 myoelastic-aerodynamic theory, which established that phonation results from interaction between air pressure, tissue elasticity, and aerodynamic forces. Ingo Titze formalized the concept mathematically in his seminal 1988 Journal of the Acoustical Society of America paper, originally terming it “oscillation threshold pressure.” His 1992 paper, “Phonation threshold pressure: A missing link in glottal aerodynamics,” cemented PTP’s importance by demonstrating its connection to aerodynamic flow parameters.

The translation from laboratory to clinical practice began with Smitheran and Hixon’s 1981 indirect measurement method using oral pressure during the voiceless bilabial stop /p/. Verdolini-Marston’s 1990 hydration study demonstrated clinical relevance, while Jiang and colleagues’ 1999 pathology comparison validated diagnostic utility. Despite four decades of research, standardization challenges persist—no universally accepted protocol exists, limiting cross-study comparisons.

Scientific Basis

Titze’s Foundational Equation

Titze derived a closed-form equation expressing PTP as a function of measurable vocal fold properties:

Pth = kt × B × c × (ξ₀₁ + ξ₀₂) / (Lg × T²)

Where:

• kt = transglottal pressure coefficient
• B = tissue damping coefficient
• c = mucosal wave velocity (0.5–4 m/s)
• ξ₀ = prephonatory glottal half-width
• Lg = glottal length (anterior-posterior)
• T = vocal fold thickness (inferior-superior)

This equation reveals that PTP increases with tissue damping, mucosal wave velocity, and glottal width, while decreasing with vocal fold thickness. The inverse-square relationship with thickness (T²) explains why thicker vocal folds oscillate more easily—a principle underlying chest voice efficiency compared to thin-fold configurations.

A simplified clinical formula captures the quadratic relationship between PTP and pitch (Solomon, Ramanathan, and Makashay, 2007):

Pth = 0.14 + 0.06 × (F₀ / F₀S)² (in kPa)

Where F₀ is the target fundamental frequency and F₀S is the individual’s mean speaking frequency (typically ~120 Hz for men, ~190 Hz for women). This approximation predicts that PTP roughly doubles when singing one octave above speaking pitch and quadruples at two octaves above.

Physiological Determinants

Vocal fold stiffness exerts the strongest influence on PTP. Zhang’s 2017 finite element modeling demonstrated that transverse stiffness has the largest effect, with higher stiffness requiring greater driving pressure. Reducing either body-layer or cover-layer stiffness lowers PTP, providing rationale for injectable treatments using soft materials like hyaluronic acid for vocal fold scarring (Mendelsohn and Zhang, 2011).

Hydration profoundly affects biomechanics. Tissue viscosity has a linear relationship with PTP per Titze’s equation. Research documents 4- to 7-fold increases in vocal fold stiffness with dehydration in excised tissue (Miri et al., 2013). These findings explain why systemic hydration and environmental humidity directly impact vocal efficiency.

Mucosal wave dynamics determine the phase difference enabling energy transfer from airflow to oscillation. The ideal wave velocity equals the product of fundamental frequency and vocal fold thickness (f₀ × T). Velocities exceeding 8 m/s prevent oscillation entirely. Titze’s 2022 research confirmed that the mucosal wave mechanism produces lower threshold pressure than supraglottal inertance alone.

Glottal geometry affects PTP through multiple pathways. Lowest PTP occurs at glottal diameters between 0.0–0.1 mm and for rectangular or near-rectangular prephonatory configurations (Chan, Titze, and Titze, 1997).

Normative Values and Fundamental Frequency Relationship

Across multiple studies, healthy adult PTP at comfortable pitch consistently falls within 3–5 cm H₂O. High pitches require substantially higher pressure—Verdolini and colleagues measured 8.52 ± 3.69 cm H₂O at high pitch compared to 3.23 ± 0.67 cm H₂O at comfortable pitch. Children ages 8–11 show comparable values around 3.6 cm H₂O (McAllister and Sundberg, 1998).

A critical phenomenon is hysteresis: the offset PTP (pressure at which oscillation ceases) is consistently 50–100% lower than onset PTP. Less energy is required to maintain oscillation than to initiate it—a finding with implications for understanding vocal fatigue, warm-up effects, and why sustained phonation feels easier than onset.

Pedagogical Considerations

Trained Versus Untrained Differences

Research consistently demonstrates that trained singers show minimal PTP elevation after extended vocalization, while untrained voices show significant increases. Enflo, Sundberg, and McAllister (2013) found singers’ PTP remained stable after 20 minutes of loud vocalization. This measurable difference provides objective evidence for vocal efficiency concepts central to pedagogy.

Semi-Occluded Vocal Tract Exercises

Semi-occluded vocal tract exercises (SOVTEs)—straw phonation, lip trills, resonance tubes—have theoretical grounding in PTP research. Titze’s 2006 paper explained that semi-occlusion increases vocal tract inertance, which reduces PTP. This provides scientific rationale for why these exercises feel “easier” and may facilitate more efficient phonation patterns.

Vocal Fatigue Assessment

PTP shows strong correlation (r = 0.91) with perceived phonatory effort during vocal loading tasks (Chang and Karnell, 2004). PTP increases significantly within the first 15 minutes of vocal loading, making it an early objective indicator of fatigue onset before subjective symptoms emerge. However, PTP returns to baseline within one hour post-fatigue, faster than subjective perception measures.

Hydration Effects

Teachers should understand that hydration interventions show measurable effects on PTP. Solomon and DiMattia (2000) demonstrated that increased water consumption attenuated PTP elevation during prolonged loud reading, particularly at high pitches. This provides objective evidence supporting vocal hygiene recommendations.

Common Misconceptions

Misconception: “Higher PTP simply means the singer is using more effort or being louder”

Reality: PTP is fundamentally a tissue property measure, not an effort measure. Elevated PTP indicates increased tissue stiffness, viscosity, or aberrant geometry rather than volitional force. A singer with healthy, well-hydrated folds requires less pressure to initiate phonation regardless of intended loudness. PTP measures threshold conditions, not sustained phonation dynamics.

Misconception: “Vocal warm-ups always lower PTP and make phonation easier”

Reality: Motel, Fisher, and Leydon (2003) found that warm-up actually increased PTP for high pitch in soprano singers (p = 0.033) while having no significant effect at comfortable or low pitches. This counterintuitive finding suggests short-term vocal exercise may increase vocal fold viscosity, potentially stabilizing the high voice rather than “loosening” it. The relationship between warm-up and ease of phonation is more complex than commonly assumed.

Misconception: “Lower PTP is always better for singing”

Reality: While efficient phonation generally corresponds to lower PTP, context matters. Some vocal configurations intentionally increase fold stiffness and thickness for specific timbral effects. Additionally, the hysteresis phenomenon means onset and offset pressures differ substantially—optimal phonation involves maintaining oscillation (lower pressure) rather than repeatedly initiating it.

Related Terms

Also known as: PTP, Oscillation Threshold Pressure (Titze’s original 1988 term)

See also: Phonation Threshold Flow (minimum airflow at phonation cessation; better reflects incomplete closure), Collision Threshold Pressure (lowest pressure facilitating vocal fold contact during phonation)

References

Chan, Roger W., and Ingo R. Titze. 2006. “Dependence of Phonation Threshold Pressure on Vocal Tract Acoustics and Vocal Fold Tissue Mechanics.” Journal of the Acoustical Society of America 119(4): 2351-2362. https://doi.org/10.1121/1.2173516.

Chan, Roger W., Ingo R. Titze, and Michael R. Titze. 1997. “Further Studies of Phonation Threshold Pressure in a Physical Model of the Vocal Fold Mucosa.” Journal of the Acoustical Society of America 101(6): 3722-3727. https://doi.org/10.1121/1.418331.

Chang, An, and Michael P. Karnell. 2004. “Perceived Phonatory Effort and Phonation Threshold Pressure across a Prolonged Voice Loading Task: A Study of Vocal Fatigue.” Journal of Voice 18(4): 454-466. https://doi.org/10.1016/j.jvoice.2004.01.004.

Enflo, Laura, Johan Sundberg, and Anita McAllister. 2013. “Collision and Phonation Threshold Pressures before and after Loud, Prolonged Vocalization in Trained and Untrained Voices.” Journal of Voice 27(5): 527-530. https://doi.org/10.1016/j.jvoice.2013.03.008.

Jiang, Jack, Tim O’Mara, David Conley, and David Hanson. 1999. “Phonation Threshold Pressure Measurements during Phonation by Airflow Interruption.” Laryngoscope 109(3): 425-432. https://doi.org/10.1097/00005537-199903000-00016.

McAllister, Anita, and Johan Sundberg. 1998. “Data on Subglottal Pressure and SPL at Varied Vocal Loudness and Pitch in 8- to 11-Year-Old Children.” Journal of Voice 12(2): 166-174. https://doi.org/10.1016/S0892-1997(98)80035-0.

Mendelsohn, Abie H., and Zhaoyan Zhang. 2011. “Phonation Threshold Pressure and Onset Frequency in a Two-Layer Physical Model of the Vocal Folds.” Journal of the Acoustical Society of America 130(5): 2961-2968. https://doi.org/10.1121/1.3644913.

Miri, Amir K., Hani E. Heris, Umakanta Tripathy, Parth U. Wiseman, and Luc Bherer. 2013. “Microstructural Characterization of Vocal Folds toward a Strain-Energy Model of Collagen Remodeling.” Acta Biomaterialia 9(8): 7957-7967. https://doi.org/10.1016/j.actbio.2013.04.044.

Motel, Tamara, Kimberly V. Fisher, and Ciara Leydon. 2003. “Vocal Warm-Up Increases Phonation Threshold Pressure in Soprano Singers at High Pitch.” Journal of Voice 17(2): 160-167. https://doi.org/10.1016/S0892-1997(03)00003-1.

Solomon, Nancy P., and Maria S. DiMattia. 2000. “Effects of a Vocally Fatiguing Task and Systemic Hydration on Phonation Threshold Pressure.” Journal of Voice 14(3): 341-362. https://doi.org/10.1016/S0892-1997(00)80080-6.

Solomon, Nancy P., Priya Ramanathan, and Matthew J. Makashay. 2007. “Phonation Threshold Pressure across the Pitch Range: Preliminary Test of a Model.” Journal of Voice 21(5): 541-550. https://doi.org/10.1016/j.jvoice.2006.04.002.

Titze, Ingo R. 1988. “The Physics of Small-Amplitude Oscillation of the Vocal Folds.” Journal of the Acoustical Society of America 83(4): 1536-1552. https://doi.org/10.1121/1.395910.

Titze, Ingo R. 1992. “Phonation Threshold Pressure: A Missing Link in Glottal Aerodynamics.” Journal of the Acoustical Society of America 91(5): 2926-2935. https://doi.org/10.1121/1.402928.

Titze, Ingo R. 2006. “Voice Training and Therapy with a Semi-Occluded Vocal Tract: Rationale and Scientific Underpinnings.” Journal of Speech, Language, and Hearing Research 49(2): 448-459. https://doi.org/10.1044/1092-4388(2006/035).

Titze, Ingo R. 2022. “How Can Vocal Folds Oscillate with a Limited Mucosal Wave?” JASA Express Letters 2(10): 105201. https://doi.org/10.1121/10.0014359.

Verdolini-Marston, Katherine, Ingo R. Titze, and David G. Druker. 1990. “Changes in Phonation Threshold Pressure with Induced Conditions of Hydration.” Journal of Voice 4(2): 142-151. https://doi.org/10.1016/S0892-1997(05)80139-0.

Zhang, Zhaoyan. 2017. “Effect of Vocal Fold Stiffness on Voice Production in a Three-Dimensional Body-Cover Phonation Model.” Journal of the Acoustical Society of America 142(4): 2311-2321. https://doi.org/10.1121/1.5008497.