Definition of pitch

The time taken by one vibratory cycle of the vocal folds is called its period.

The frequency of vibration is, therefore, the number of periods per second. This is measured in Hertz (Hz):

1 Hertz = 1 vibration/second

Now, frequency is perceived by the human ear as the pitch of the sound, i.e.

• the higher the frequency, the higher we perceive the pitch to be
• the lower the frequency, the lower we perceive the pitch to be

Figure 1. Low frequency wave.

Figure 2. High frequency wave (perceived to be at a higher pitch than the wave show in Fig. 1).

Fundamental frequency

A person’s habitual pitch, or speaking fundamental frequency (SF₀), largely depends on their sex and age. However, it will also be affected by such things as the type of communication being undertaken, the speaker’s emotional state, background noise, reading aloud, talking on the telephone, the degree of intoxication if the speaker has been drinking alcohol, and so on (Mathieson, 2001:76).

Typically, men have a lower SF₀ than women, who have a lower SF₀ than children (Table 1).

Table 1. Average Speaking Fundamental Frequencies.

[Source: Howard (1998) and Mathieson (2001)]

Varying pitch

Humans can make considerable voluntary variations to the pitch of the voice, but how is this achieved? Well, consider the sound produced by blowing across a stretched elastic band. If the elastic band is thin it has less mass and it will, therefore, be able to move more quickly for the same amount of force. Consequently, the note produced is higher in pitch. If you now change this elastic band for a thicker one the note produced will be lower (provided you are blowing with the same force and the band is stretched the same amount). This is because the elastic band is more massive and it, therefore, moves more slowly. The resultant pitch is consequently perceived to be lower.

Another way to alter the pitch, whilst blowing across the same elastic band, is to stretch it further. By increasing the tension in the elastic this has a similar effect to making the elastic band thinner. It again moves more quickly for the same amount of force and the pitch is higher.

With respect to the human larynx it is, of course, not possible to change the vocal folds for a thinner set every time we wish to produce a higher pitch. The major mechanism for altering pitch is, therefore, to variously stretch and relax the vocal folds. This is largely achieved through rotational and sliding movements of the arytenoid cartilages and the tilting of the cricoid cartilage in relation to the thyroid cartilage (see Larynx).

Figure 2. Diagram of the larynx.

Frequency range of speech

Human speech is usually produced in the range of about 100-10,000 Hz.

References

Howard, D.M. (1998) ‘Instrumental voice measurement: uses and limitations’ in Harris, T., Harris, S. Rubins, J.S. and Howard, D.M. (eds) The Voice Clinic Handbook London: Whurr.

Mathieson, L. (2001) Greene and Mathieson’s The Voice and Its Disorders (6th edn) London: Whurr Publishers.