NAQ: Vocal Fold Closure Quality (A Parameter Invisible on the Spectrum)
NAQ measures how "tightly and cleanly" the vocal folds close — it hides behind the spectrum and can only be seen through "inverse filtering".
The previous parameters can all be "read" off the spectrum. But NAQ (Normalized Amplitude Quotient) cannot — it describes how the vocal folds close. The sound is colored by the vocal tract before reaching the mic, so the app models the tract with LPC, then performs inverse filtering to "peel off" the tract and recover the glottal airflow pulse, then measures: total airflow (AAC) ÷ closure speed (dpeak).
Experiment 11 · Three Fold States, Three Pulses
Switch between three closure modes and watch the fold animation plus the inverse-filtered glottal airflow pulse: Pressed (hard closure, airflow trapped, NAQ<0.1) · Flow (crisp closure, smooth airflow, 0.1–0.25 ideal zone) · Breathy (doesn't close fully, leaking, NAQ>0.3).
NAQ is a "closure quality" reading, not a leakage percentage. 0.5 does not mean 50% of your air leaks — it is a dimensionless ratio. This is exactly what the app's vocal fold closure chart shows. Related: vocal fold closure chart