Study on some aspects of the “singer's formant” in north indian classical singing

journal of Voice

Vol. 4, No. 2, pp. 129--134 © 1990Raven Press, Ltd., New York

Study on Some Aspects of the "Singer's Formant" in North Indian Classical Singing Ranjan Sengupta Scientific Research Department, Sangeet Research Academy, Calcutta, 700 040 India

Summary: This article deals with a spectrographic analysis of the singer's formant as occurred during singing of the vowels/a/, h/, and/o/in North Indian classical vocal music. The resonance balance, center frequency, and bandwidth are shown as a function of fundamental frequency for eight singers. Two new parameters have been defined viz. asymmetry parameter (A) and spectral energy balance (W). Their variation with fundamental frequency is shown. Key Words: North Indian--Singing--Spectrogram--Vowel formants-Bandwidth--Fundamental frequency--Resonance balance--Asymmetry parameter-Spectral energy balance.

Studies on the voice and voice qualities of singers are carried on throughout the world by different techniques, and it is a common observation that vowel quality differs between speech and professional singing (1). The question therefore arises regarding the physiological differences between speaking and singing that govern the differences in their articulation. Although most of the works state that the vertical laryngeal position plays a vital role in discriminating between the trained singer's voice and normal speaker's voice (2-8), some authors opine that the larynx height is not a reliable way to distinguish those voices (9). Formants associated with good (brilliant) voice in singers have been studied by many authors (10-12). It was concluded that the "Singer's formant," which is an unusually high spectrum envelope peak near 2.8-3.2 kHz, located between third and fourth formants of vowel sounds, is observed in male opera and concert singers (13). Some authors also showed the need for a singer's formant in female voices (14). Another interesting circumstance is that the frequency of this formant approximately coincides with the region of maximal sensitivity of the human ear. Consequently, the presence of the

singer's formant may make the sung sound easier to perceive (15). It is open to question now whether the singer's formant alone or when associated with other higher formants is responsible for the production of a good timbral voice in classical voice music. Throughout its long history, North Indian Classical Vocal Music has developed meditative investigations and practice based mainly on judgement and aesthetic values. The purity of tune (scale), the purity of phonation (vocalization), and the quality of voice (sweetness) were once judged by the unaided auditory process in the earlier years of development, and no systematic acoustic investigations into those factors have been done so far. Although there is a marked difference between the voice culture technique and the style of singing between Western and Indian classical music, the presence of the singer's formant was observed in the acoustic spectra of both male and female exponents of North Indian Classical singing (16). In this article, we have analyzed and discussed several aspects of the singer's formant in male and female sung vowels by trained singers of North Indian Classical singing. EXPERIMENTAL METHODS

Address correspondence and reprint requests to Dr. R. Sengupta at Sangeet Research Academy 1 N.S.C. Bose Road, Calcutta 700 040, India.

Four male and four female singers ranging in age from 17 to 30 years were chosen as subjects for the 129

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experiment. Each one had more than five years of musical training under expert musicians of North Indian Classical Music. They were asked to sing the vowels /a/, /i/, and /o/ over their full vocal range twice a day and twice a week for 6 months in the presence of their masters, who certified that their vocal production was appropriate for singing. Most of them covered a two to two-and-a-half octave range. The above vowels were chosen because of their wide applications in North Indian Classical Music. This was recorded on a AIWA stereo cassette recorder (model 3600) by keeping the AKG microphone (Model 310) 17 cm from the singers mouth in a sound proof studio (dimensions 18' x 16' x 12') having a reverberation time of 500 ms. Spectrograms were taken with the help of a Digital Sonagraph (Kay Elemetrics, model 7800) with a printer (Kay Elemetrics, model 7900) over the frequency range DC to 8 kHz using both narrow band (BW 45 Hz) and wide band (BW 300 Hz) filters. The PWR spectra (frequency vs. amplitude) were taken at the steady positions of each note. The study was concentrated in the two regions of the spectrum, i.e., (a) a region of vowel definition (in frequency up to 1.8 kHz), (b) region of singer's formant (2--4 kHz). A vowel can be defined with the help of the first two formants (F1 and F2). The mean of the two partials that have the highest amplitudes in the vowel definition region are taken for each vowel and designated as Fv. Similarly, the spectral position of the singer' s formant is indicated by the high-

est partial (in amplitude) or by the middle of the interval between the two highest partials (in amplitude) in the singer's formant region (Fs). In both the aforementioned regions the peak values of the two highest partials were taken. The mean of the two peaks in the vowel definition region was then calculated (Lv) and compared with the mean of the two highest peaks in the singer's formant region (Ls). The difference in decibels between both mean values gives a measure of "resonance balance" (R) (17,19) i.e., R = Lv - Ls (dB). RESULTS AND DISCUSSIONS Fig. 1 shows a three-dimensional (3D) spectra (sonagram) of five notes ascending in succession, on the vowel/o/ sung by a trained male vocalist. The singer's formant is observed and its bandwidth increases with rising pitch. Fig. 2 shows the 313 spectra (sonagram) of the vowel/o/, spoken by the same male singer. Absence of singer's formant is very well observed. PWR spectra (frequency vs. amplitude) in the steady part of a note, in the vowel /a/sung by a trained female vocalist, are shown in Fig. 3. In Fig. 4 we have shown three aspects of the singer's formant. In the upper figure, center frequency of the singer's formant (Fs), as obtained from the spectrograms, is plotted against the fundamental frequency (F0) for eight trained vocalists (four male and four female). The vocalists sang vowel/a/, which is the most practiced vowel in the

FIG. 1. Three dimensional spectra of the five notes sung in succession in case of vowel/o/, by a male vocalist, depicting the singer's formant in the region of 2.5-3.3 kHz. The bandwidth increases with rising pitch. Journal of Voice, Vol. 4, No. 2, 1990

SINGER'S FORMANT IN NORTH INDIAN CLASSICAL SINGING

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FIG. 2. Three dimensional spectra of spoken vowel/o/by the same male vocalist. Absence of singer's formant is very well observed.

North Indian Classical vocal music, over their complete vocal range. It is observed from the figure that the center frequency of the singer's formant increases slowly with an increase in pitch, which is similar to the sung vowels in Western music. The - 15 dB bandwidth (kHz) of the singer's formant is shown as a function of the fundamental frequency (F0). The bandwidth increases with an increase in fundamental frequency and it is close to five times F 0 for lower F o. The lower part of the figure shows the resonance balance in dB as a function of fundamental frequency (Fo) in the case of the ANALYSIS BY

FIG. 3. PWR spectra in the steady part of a note, sustained for 800 Ins in case of vowel/a/, sung by a trained female singer. Singer's formant is - 3 kHz.

sung vowel/a/for eight singers. Resonance balance is calculated by the method adopted by Schutte and Miller (17). It appears to be rather stable, i.e., about - 4 dB around the fundamental frequency values in their middle octave (230-400 Hz), and then decreases slowly as the pitch increases. Table ! shows the value of average dispersions within the male and female groups, and then between male and female groups, for eight singers. Fig. 5 (17) shows the spectral position, resonance balance, and - 15 dB bandwidth plotted against the fundamental frequency (Fo) for the v o w e l / ~ / s u n g by a male tenor who was highly skilled in Western music. The results are similar as in North Indian Classical music. During singing, an automatic error control feedback mechanism operates to preceive the defects, and conscious efforts are made to rectify them. The inadequacy of this feedback was responsible for the larger degradation of both phonetic and musical qualities of the voices in the highest notes. We have therefore defined an "asymmetry parameter." [A = Fs - Fv/Fs + Fv] Fs and Fv have been defined earlier. In Fig. 6, A is shown as a function of the fundamental frequency for three vowels/a/,/i/, and /o/, sung over the complete vocal range by eight trained vocalists (four male and four female),4n North Indian Classical vocal music. Quite interestingly, it is observed that " A " maintains a steady value of -0.61 over their complete vocal range irrespective of the vowel. It may be stated from here that a steady value of A reflects good control over their vocal organs regarding phonation of the vowJournal of Voice, Vol. 4, No. 2, 1990

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VOWEL / a / ~--:~ 4"0 L-_ . . . . . .

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els, and a better control over their larynx for generating a steady singer's formant. It is observed from the figure that the singers have better control over their vocal organs for some specific values of F 0 (which are the prominent and most practiced notes in North Indian style). The phonetic quality remains more or less undistorted if A remains in and around - 0 . 6 1 . Also when A = 0.61 the production of the singer's formant is perfect with a steady bandwidth. Distortion in the vowel and in the nature of the singer's formant increases with the change in the value of A. Therefore A can be designated as a measure of the error control f e e d b a c k m e c h a n i s m . T o p r o d u c e a wellf o r m e d singer's f o r m a n t without distorting the Journal of Voice, Vol. 4, No. 2, 1990

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vowel, a singer must maintain the value of A in and around - 0 . 6 1 . Realizing the fact that the energy values would be some help in getting more information about the T A B L E 1. Values o f average dispersions (cr) a m o n g and

across male and f e m a l e groups

Spectral position of the singer's formant Bandwidth of the singer's formant Resonance balance

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Between women

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SINGER'S FORMANT IN NORTH INDIAN CLASSICAL SINGING

133

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singer's formant, the acoustical energy concentrations were observed for both the vowel definition region and the singer's formant region from the PWR spectrum. Their ratio (i.e., the area of the energy contour in the vowel definition region divided by the area of the energy contour in the singer's formant region) gave a measure of "spectral energy balance" (W). In Fig. 7, we show spectral energy balance (W) for all the three vowels,/a/,/i/, and/o/, sung by a male singer in his complete vocal range, as a function of his fundamental frequency (F0). It is observed that the spectral energy balance

(W) decreases very slowly with the increase of voice fundamental frequency (Fo). CONCLUSIONS Summerizing we can say: (a) In all the cases (irrespective of gender) the center frequency of the singer's formant increases with an increase in pitch. (b) The resonance balance increases with an increase in pitch both for male and for female singers and maintains a steady value around - 4 dB in the middle octave region for the low back vowel/a/. (c)

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Journal of Voice, Vol. 4, No. 2, 1990

134

R. SENGUPTA

formes, and sinus morgagni for producing the singer's formant in the acoustic spectra.

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- 15 dB bandwidth, for the vowel/a/, increases rapidly with a rise in pitch and it is approximately five times the fundamental frequency for the lower value of fundamental. This may be due to the rising of the larynx with Fo. The amplitude of Fo also decreases with increased pitch. (d) The asymmetry parameter remains more or less constant with the change in F 0 independent of the vowel. "A" maintains a steady value of -0.61 for some specific value of Fo (i.e., notes that are more practiced). An error control feedback mechanism perfectly operates for these notes, thereby producing undistorted vowels with well-formed singer's formant. (e) The ratio of the spectral energy concentration in the vowel definition and singer's formant regions, defined as spectral energy balance (W), decreases slowly with a rising pitch. This experimental analysis on the nature of the singer's formant in North Indian Classical vocal music will be helpful in framing and modifying the models regarding the role of larynx, sinus piri-

Journal of Voice, Vol. 4, No. 2, 1990

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