[noumenal]

Singer’s formant.

The ‘singer’s formant’ is a peak in the spectrum envelope typically appearing near 3 kHz in all voiced sounds as sung by Western operatic singers except sopranos. It corresponds acoustically to a high spectrum envelope peak which is present in all vowels and generally centred at a frequency of 2500–3500 Hz. In vocal pedagogy it is often referred to as ‘singing in the mask’, ‘focussing’ etc. Mainly a resonatory phenomenon, the singer’s formant is achieved by clustering formants 3, 4 and 5 into a rather narrow frequency band. This seems to explain why sopranos lack a singer’s formant: they mostly sing at high fundamental frequencies, i.e. the frequency distance between adjacent partials is typically quite wide, equalling the frequency of the fundamental. This means that a partial would fall into the frequency band of the formant cluster producing the singer’s formant only for certain pitches, causing a salient timbre difference between different pitches. If the pharynx is wide enough, the larynx tube can act as a separate resonator, the resonance frequency of which is rather independent of the rest of the vocal tract; it may be tuned to a frequency lying between those of the third and fourth formants in normal speech. The condition of a widening of the pharynx seems to be met when the larynx is lowered, a gesture occurring typically in male professional Western operatic singing. At high pitches the demands on a wide pharynx are increased, and extreme lowering of the larynx is frequently observed when males sing high-pitched notes. In such cases the term ‘covering’ is sometimes used. The widening of the pharynx and the lowering of the larynx affect the frequencies not only of the higher formants, but also those of the lower formants. As an acoustical consequence of such articulatory modifications, the frequency of the second formant drops in front vowels. This alters the vowel quality to some extent, so that, for instance, the vowel in ‘sheep’ is ‘coloured’ towards the German ‘ü’ sound.
The perceptual function of the ‘singer’s formant’ seems to be to make the voice easier to hear above a loud orchestral accompaniment. It has also been suggested that it helps the singer to be more audible in large auditoriums.



High-pitched singing.


Vowel quality is associated with specific combinations of the two lowest formant frequencies, and these frequencies are maintained regardless of the fundamental frequency. Normally the fundamental frequency is lower than the frequency of the first formant, which varies between about 250 Hz (close to c') and 1000 Hz, depending on the vowel. When the fundamental frequency is higher than the normal frequency value of the first formant, singers tend to increase the latter so that it remains higher in frequency than the fundamental. This partial is the strongest in the source spectrum, and, if it coincides with the first formant frequency, its amplitude will be maximized without raising extreme demands on vocal effort. The degrees of tongue constriction and, in particular, of jaw opening represent important articulatory tools for achieving the necessary increases of the first formant frequency. Though this increase affects vowel quality, this disadvantage is limited since in high-pitched singing the vowel quality cannot be maintained even with correct formant frequencies owing to the great frequency distance between the partials as compared with the number of formants (see Sundberg and Skoog, 1997).
Voice categories.

Male and female voices tend to differ significantly with regard to their formant frequencies as well as pitch range, and this factor seems also to be significant in differentiating tenors, baritones and basses. Thus when singing the same pitch, voices of these types can be distinguished by their vowel formant frequencies. In most vowels a bass is likely to show the lowest formant frequencies and a tenor the highest; and all formants, not only the two lowest, are relevant. The formant frequency differences between male and female voices resemble closely those observed between bass and tenor voices, which suggests that the dimensions of the resonating system are of major importance. In addition, the centre frequency of the singer’s formant seems to be typically higher in voices with a high pitch range than in voices with a lower pitch range. Thus, centre frequencies at about 2400 and 3000 Hz tend to give a bass-baritone-like and a tenor-like voice quality respectively.
Overtone singing.

In some Inner Asian cultures the voice is used in a rather special manner, in that the tones produced are perceived as possessing two different pitches. This can be explained as follows. If the frequency of a formant coincides with that of a partial, this partial is likely to be much stronger than the adjacent spectrum partials, other things being equal. If two formants are tuned to the near vicinity of a partial, the effect can be greatly enhanced, so that the partial is perceived as a second pitch of the tone along with the fundamental. This strategy of tuning two formants to a partial is applied in overtone singing. The second and third formants (sometimes the first and second) are tuned to closely spaced frequencies, thus enhancing a specific partial. The fundamental frequency is either low, <100 Hz, produced with a growl or vocal fry quality, or is higher, often with a pressed quality. By these means the amplitude of the fundamental is reduced, and hence the dominance of the amplified overtone is enhanced. In tuning formants the lip opening, the position and elevation of the tongue tip and, in some cases, nasalization seem to play important roles.