The Frequency Characteristics of Speech

Figure 7. A frequency analysis of a typical vowel having a single resonance region.

The fundamental pitch of the vowel sounds is subject to wide variations by changes in the vocal cords. The vowel sounds are characterized by resonant regions which are independent of the fundamental, and which determine the particular vowel sounded. Certain vowels, as shown in Fig. 7, are single-resonance vowels. Others have two regions of resonance, as Fig. 8 illustrates. The fundamental pitch in which the vowels are spoken has a decided influence on the spacing of these resonance points.²¹ The characteristic frequencies of the semivowels and the nasal consonants are almost entirely below 3000 cycles. The stop and fricative consonants lie, for the most part, above 2000 cycles.

Figure 8. A frequency analysis of a typical vowel having two resonance regions

The complicated nature of speech sound waves and the electromagnetic waves used to transmit speech electrically can be seen from Fig. 9.

Figure 9. Wave form of the word "seems.".

Although the pitch of the voice in speaking the vowels varies for different individuals, it is as low as about 90 cycles per second for a deep-voiced man, and as high as about 300 cycles for a shrill-voiced woman. The harmonics, or overtones, go as high as about 6000 cycles. In singing, the fundamental frequencies of the voice cover an approximate range from about 60 cycles for the lowest note of the bass voice to 1300 cycles for the high notes of a soprano; the overtones go as high as about 10,000 cycles per second.

Extensive tests have shown that it is not necessary to transmit all the frequencies present in speech or music sound waves.