f0	Mean fundamental frequency of the voice recording; this relates to the overall pitch of the voice.
LTF2	Long-term formant distribution (LTF) of the second vowel formant* frequency (F2). As an average of all vowels in the recording, LTF2 conveys information about general vocal tract settings and vocal tract size. See Moos (2010) and Nolan and Grigoras (2005) for more details on using LTF.
Spectral tilt	Energy distribution across the frequency range measured in one accented vowel per recording (“apparently” for sentence 1, “ever” for sentence 2). Spectral tilt is the extent to which energy in the signal falls off as frequency increases: energy at higher frequencies is less damped when spectral tilt is shallow and more damped when spectral tilt is steep. It relates to various physiological characteristics of vocal fold vibration, including the proportion of the vibratory cycle during which the folds are open, and the abruptness or gradualness of vocal fold closure. BREATHY voice, e.g., is associated with a steep spectral tilt, CREAK and HARSH among others with a shallow tilt. Spectral tilt was quantified here using measures of the corrected first harmonic minus the corrected amplitude of F3 (H1*-A3*) (see Hanson, 1997 for further details).
Pitch range	Variability of f0 in a speaker, calculated by subtracting the minimum from the maximum pitch of a voice recording and converting to semitones. This describes the differences between (for example) a “singsongy” vs. monotonous voice (i.e., large vs. small pitch range).

^*Formants are spectral peaks of intensity at different frequencies (usually measured in Hz) in the frequency spectrum of the sound. They are created by the resonances of the vocal tract (Clark et al., 2007). A vowel sound contains several formants. The lowest two formants mainly characterize the vowel quality, while all formants additionally give information about speaker characteristics.