We demonstrate here a selection of relevant musical attributes, or parameters, describing the singing voice. Specifically we demonstrate four binomial cases denoting the existence or non-existence of the parameter. These cases include singer's formants vs. flat voice, falsetto register vs. modal register, breathiness voice vs. limpid voice and portamento.
We include also a demonstration of the perceptual effect of the frequency and semitone extension of the vibrato on a singer voice.
Singer's formant vs. flat voice
The singer formant promotes an enhanced energy at frequencies of about 2000, 3000 and 4000 Hz. This reinforcement, typically, results from the concentration of formants 3, 4 and 5. This feature makes it possible for the voice of a singer to stand out from the sound of an orchestra. It is also associated with the perceived quality on performance of the singer in terms of singing in a clear and comfortable way while making an effective usage of acoustic energy.
The level and center frequency of this “super” formant is related to the fundamental frequency, emitted vowel, to the intensity, among other acoustic factors. The singer formant center frequency, according Johan Sundberg [ref], is related to the type of the voice, which was found to be lower for singers classified as a bass and higher for tenors. The same study also showed that for most soprano voices, two peaks are observed in the singer's formant, which suggests that the underlying formants that are not very close.
Acoustically, with the use of singer’s formant, typically there is a significant increase in the energy of harmonic components in the vicinity of the 3000 Hz region, causing them to exceed the energy of the fundamental harmonic. In the flat voice, unlike the use of singer’s formant, the component with more energy is the fundamental harmonic, and the voice, in this case, has low power compared to the use of singer formant. These acoustic features can be seen in the following figures which illustrate the magnitude spectrum on both cases.
Singer Formant - female example
Singer Formant - male example
Flat Voice - female example
Flat Voice - male example
Falsetto vs. Modal voice
The falsetto register is produced as a result of the vibration of a fraction of the vocal folds. Usually the term falsetto is associated with male voices, and the head voice is associated with female voices.
The antagonistic term is the modal or chest register. The difference between these registers lies in the different forms of vocal fold vibration resulting from different forms of adduction.
The falsetto is the register used by the singer in the phonation of a higher fundamental frequency of a non-natural (and therefore false, Falsetto = false) tone. The result is a lighter and softer register that contrasts with the profound, dense and audible register that is "chest" register.
The falsetto has higher energy expenditure, since only parts of the vocal fold are used. Typically the amplitude of the voice is reduced. Acoustically, the voice has a lack of harmonics (especially in the region of high frequencies) due to a lack of vigor in the use of resonances. This translates into a sharp timbre difference between modal and falsetto registers.
The falsetto is usually associated with the production of sound with high fundamental frequency on an unnatural manner, and therefore consists of a technique that requires lots of practice. Normally it is detected when a singer produces sounds whose fundamental frequency is higher than the upper limit of his/her modal register.
As mentioned, acoustically, falsetto is associated with the loss of energy of high frequency harmonics, along with increased energy of the fundamental. Thus, the fundamental component, in the falsetto register, will be prominent in relation to the singer's formant. The following figures which represent the magnitude spectrum on both cases, illustrate these aspects.
Falsetto register - female example
Falsetto register - male example
Modal register - female example
Modal register - male example
Breathiness vs. Limpidity
Breathiness is related to the amount of air expelled during phonation. It is typically a result of a glottal slit and it may be associated with pathological phenomena in the case of speaking voice, or a deficit of respiratory support in the case of singing voice.
Acoustically, the existence of breathiness is associated with a reduced value of an important acoustic feature measuring voice quality and knowing as harmonics to noise ratio; as it can be seen in the following figures representing spectral magnitude. Perceptively a background noise is dearly audible in a breathy voice.
Aesthetically breathiness and limpidity can coexist or not in some singing styles, but in lyric singing breathiness is regarded as a deficit of technique while in other styles as Country, Folk or Jazz is a habitual characteristic.
Breathiness Voice - female example
Breathiness Voice - male example
Limpidity Voice - female example
Limpidity Voice - male example
Portamento derives from the Italian word while means "transport". It denotes a connection between two notes made by sliding between the initial note and the final note, so that intermediate notes are perceptible. The indication for the use of this technique is usually described in the score, however, when it is used without indication it is usually considered like a lack of technique or aesthetic sense.
As can be seen in the following figure, the transition with portamento is slower than the transition without portamento, causing the intermediate notes to be audible.
With Portamento - female example
With Portamento - male example
Without Portamento - female example
Without Portamento - male example
Vibrato is an almost periodic variation of the fundamental frequency, which can be combined with variations of intensity, enriching the sound produced and even its timbre. The vibrato frequency is usually considered constant for each singer and is very difficult to be changed through training.
Vibrato can be measured in terms of extension (in the case of frequency modulation, in half-tones) and through rate (number of cycles per second or Hz; the normal is between 5.5 and 7.5Hz).
The absence of vibrato is usually knowing as white voice, a voice from a child before the onset of puberty. It is characterized by a pure tone and the absence of vibrato is its main feature. In certain musical styles such as Renaissance music, where the vibrato is used only as an ornament, it is usually denoted as "smooth voice".
The following video illustrates the effect of variation of two measures of vibrato, the frequency (in Hertz) and the extension (in semitones). These examples were prepared with the aid of a singing voice synthesizer, and therefore do not sound very natural.