What is Pitch?

Pitch is Perceptual

When listening to how "high" or "low" a voice is we often hear a description of the pitch being high or low.  Pitch is a perceptual measure of the voice--a psychological feature that we as the listeners are deciphering.  It isn't necessarily a physical feature or measure of what the larynx and vocal folds are doing.  What you might perceive as a high-pitched voice, another person may perceive as a "neutral" or low-pitched voice.

Pitch is a sensation, and is the way in which frequency changes and differences are perceived by the listener.  It can only be measured by asking listeners to make judgments.

Frequency is Physical

The frequency of the speech signal is what constitutes its perceived pitch.  When the vocal folds are set into motion with airflow from the lungs, they begin a vibratory pattern that begins moving air molecules away from them (the source of the sound).  This disturbance takes the form of a pressure wave that radiates outward.  The number of vibratory cycles that the vocal folds produced is measured in seconds, and the higher the number of cycles (frequency of vibration), the higher the perceived pitch will be

The sound becomes a wave of motion of air particles traveling longitudinally, and is commonly represented as a waveform, seen here:

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A waveform is a representation of both time and amplitude which is the physical feature of loudness.  The wider the waveform, the higher the amplitude and thus perceived loudness of the voice.

Science Learning Hub provides another great explanation of how a sound wave is a measurement of frequency and amplitude.

Although the waveform gives us information of time and loudness, it doesn't really show much about the pitch of a sound.  What we can use, then, to get a better idea of this is called a spectrogram which looks like this:

When a voice sample is recorded and its spectrogram is analyzed, we are able to identify the average rate of vibration of the vocal folds and obtain the vocal folds' fundamental frequency (F₀).  The F₀ is what is often referenced when we refer to the "pitch" of a sound, and is measured in Hertz (Hz).  So, a sound source with a F₀ of 150 cycles per second is measured as 150 Hz.  

In the image above time is along the horizontal x axis, F₀ is on the vertical y axis, and intensity (loudness) is color-coded according to the right vertical bar.  So, we can get a 3-dimensional view of the voice with a spectrogram.  Kind of cool!

The Chrome Music Lab has a great interactive spectrogram you can use to see how different sounds (including your voice) look in real time!

When measuring voice, there is quite a bit of normative data on fundamental frequency during speech for males and females.  Males typically produce fundamental frequencies between 100 and 150 Hz, whereas females produce frequencies between 180 and 250 Hz (Hollien, Dew, & Phillips, 1971).  So, perceptually, the "pitch" of female voices is higher than that of males.

What's a Typical Fundamental Frequency?

Here is a breakdown of average F₀ by sex and age taken from various sources:

Age Range	Mean F0	Standard Dev.	Range
Males Reading
7	294	2.2
8	297	2
10	270	2.4
11	227	1.5	192-268
14	242	3.4
19	117	2.1	85-155
Adult	132	3.3
20-29	120
30-39	112
40-49	107
50-59	118
60-69	112
70-79	132
80-89	146
Females Reading
7	281	2
8	288	2.8
11	238	1.51	98-271
19	217	1.71	65-255
20-29	224	3.8	192-275
30-40	196	2.5	171-222
40-50	189	2.8	168-208
60-69	200	4.3	143-235
70+	202	4.7	170-249
80-94	200	2.7	183-225

1. Fairbanks, Wiley, & Lassman, 1949.
2. Horii, 1983.
3. Fitch & Holbrook, 1970.
4. Snidecor, 1943.
5. Hollien & Shipp, 1972; Shipp & Hollien, 1969.
6. Fairbanks, Herbert, & Hammond, 1949.
7. Stoicheff, 1981.
8. Saxman & Burk, 1967.
9. McGlone & Hollien, 1963.

We can see that before adolescence males tend to have higher F₀ than females, and that with age both genders' F₀ declines during adulthood, but begins to rise again once we become seniors.  These fluctuations are due in large part to changes in the size and shape of the larynx and vocal folds with age, which changes how they vibrate and consequently changes their F₀ and perceived pitch.

Changing F₀ & Pitch

By altering the shape of the vocal folds we are changing how they vibrate.  Consider plucking a taut versus loose rubber band; the taut rubber band will vibrate with more frequently and for a longer period of time than the loose rubber band.  Using what we've discussed, we know that the higher the number of vibratory cycles, the higher the perceived pitch.  

The vocal folds function in a similar fashion--with more taut, elongated vocal folds we produce a higher F₀ and pitch.  We can change the size and shape of our vocal folds using a number of muscles to pull and tilt the cartilages and surrounding muscles.  Trained singers become quite adept at frequent alterations of the larynx to achieve quick and precise alterations in the shape of the vocal folds.

There is an emergence of interest in using pitch as a measurement of gender identity.  Multiple studies have found that the two largest factors we use when perceiving a voice as male or female is F₀ and resonant frequencies (a separate post!), with F₀ taking the lead role.  There is, hence, a great interest in altering F₀ to achieve a more masculine or feminine perception of the voice, particularly for transgender individuals who which to be perceived as the correct gender.

So now we have some science behind what pitch really is and how it can vary between individuals.  In the future we will talk more about applying this science to alter vocal production for achieving a more desirable voice.  Feel free to post questions or comments!