Measurable Parameters of Speech and Acoustics

Vocabulary terms and definitions covering measurable acoustic parameters of speech sound waves, wave composition, resonance, scales of frequency and intensity, and vocal parameters.

Vocal fundamental frequency (VFF)

The rate of vibration of the vocal folds, defined as the rate at which the vocal folds open and close.

Segmental vibration

Wave-like vibration that begins at the opening of one end and continues the length of both vocal folds, producing harmonics.

Harmonics

Multiples of the fundamental frequency generated by the segmental vibration of the vocal folds.

Pitch

The psychological correlate of frequency that listeners rate on a continuum from high to low.

Pure tone

A simple sound that contains only one frequency, exemplified by a whistle.

Complex sound waves

Sound waves composed of more than one frequency, including all speech sounds.

Phonation

In periodic sound waves, the complex sound produced by vocal fundamental frequency and harmonics via vocal fold vibration.

Aperiodic sound waves

Sound waves resulting from turbulent air forced through a restricted opening without a repeated vibrational pattern, such as the sound /s/.

Resonance

The selective amplification and dampening of frequencies in a sound resulting from the reflection and concentration of sound waves in a cavity.

Natural resonating frequency (NRF)

The specific frequency inherent to a cavity at which nearby frequencies are amplified while distant frequencies are dampened.

Harmonic analysis

The breakdown of complex periodic sounds into sinusoids (simple sound waves or pure tones) that are integral multiples of the fundamental frequency.

Octave

The basic unit of frequency on the musical scale, organized as a logarithmic scale with a base of $2$ where the frequency ratio from one octave to the next is $2$.

Semitone

A discrete division of the musical scale equal to half of a tone, with $2$ semitones per tone and $12$ semitones per octave.

Orchestral standard scale

A musical frequency standard based on $A_4 = 440\,\text{Hz}$ or $C_0 = 16.35\,\text{Hz}$, which orchestras use to tune to the first violin.

Bel

The initial logarithmic unit of intensity based on a base of $10$, where a sound $10$ times greater in intensity equals an increase of $1$ bel.

Decibel (dB)

A unit of intensity equal to one-tenth of a bel, derived by dividing the bel scale into $10$ units.

Sound pressure level (SPL) reference base

The baseline intensity of approximately the quietest sound humans can hear, established at $0.002\,\text{dynes/cm}^2$.

Power

The original measure for electrical potentials referring to the amount of work completed, expressed in units of $\text{watts/cm}^2$.

Pressure

An acoustic measure referring to the rate at which work is completed, measured in $\text{dynes/cm}^2$.

Habitual pitch

The modal fundamental frequency, referring to the fundamental frequency used most often by a speaker during daily speech.

Natural pitch

The fundamental frequency most efficient for a speaker that sounds best within their pitch range, falling $1/4$ to $1/3$ from the bottom including falsetto, or $1/3$ excluding falsetto.

Optimal pitch

The fundamental frequency that is healthiest and best for an individual, which ideally matches the speaker's natural pitch.

Falsetto pitch

A pitch produced approximately one octave above habitual pitch by holding the posterior portion of the vocal folds tightly together, reducing the vibrating length by approximately one half.

Jitter

Frequency perturbation, defined as the cycle-to-cycle variation in vocal fundamental frequency, objectively associated with the perception of vocal harshness.

Shimmer

Amplitude perturbation, defined as the cycle-to-cycle variation in vocal amplitude, objectively associated with the perception of vocal harshness.