Bravi, P. (2012). Measurements of Vibrato Parameters in a Performance of Sardinian Traditional Sung...

7/27/2019 Bravi, P. (2012). Measurements of Vibrato Parameters in a Performance of Sardinian Traditional Sung Poetry. In M.

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Atti del VIII Convegno dellAssociazione Italiana Scienze della Voce

MEASUREMENTS OF VIBRATO PARAMETERS IN APERFORMANCE OF SARDINIAN TRADITIONAL SINGING POETRY

Paolo BraviConservatorio di Musica di Cagliari

[email protected]

1. SUMMARY

Artists and Sardinian music experts agree in considering vibrato an essential feature of

the traditional singing styles of Sardinia. According to many of them, Sardinian vibrato is

something typical. It is deemed like a stylistic seal of the traditional vocality of the Island,

a kind of ornamentation different from the vibrato of other singing styles.

No formal analysis has been carried out so far to shed light on this aspect of vocal or-

namentation. In this paper, measurements of the acoustic features of vocal vibrato in four

singing poets are presented and discussed. The research corpus includes 506 segments of

vibrato that have been recorded during a real performance held in a small village of South-

ern Sardinia in Summer 2010, a poetic contest named cantada campidanesa performed by

the improvising/singing poets (cantadoris) with the accompaniment of a two-part choir (su

bsciu e contra).

On one hand the results of the analysis show the heterogeneous characteristics of the

poets, on the other they stress the tendency towards a vibrato with high rate (up to 8 Hz),

narrow extent(not exceeding a mean value of0.4 st) and a notable waving in the overall

intonation, the latter being measured with reference to the spread between the overall F0

mean and the moving mean between adjacent peaks in each segment. In a second step of

the analysis, vocal timbre (i.e. singing on different vowels), pitch (singing on different scaledegrees) and duration have been tested as prospective predictors of variability in the exam-

ined vibrato features. Whereas vocal timbre does not seem to be a valid explaining factor

(apart from one exception), scale degree and duration are able to account for the variance in

various respects.

2. INTRODUCTION

Sardinian traditional music comprises many distinct vocal and instrumental genres and

styles. While some characteristics are relevant only to some of them, others occur in most

or all of them. The attitude towards a strong ornamentation of melodies belongs to the latter

ones. It can be remarked all over the Island, both in instrumental and in vocal styles.

Particularly in the Southern part of Sardinia, flourishing art is considered an essential

part of the musicians skill and a major characteristic in the vocal practice. According toGiovanni Meloni, a renowned guitar player of traditional music, the art offroriduras

(flourishes, ornamentation) is to be considered an essential aspect of the musical idiom

of Southern Sardinia:

Nosus, in su Campidanu e in su Sulcis specialmenti, amaus meda, stimaus de fai fro-

diduras, poita ca funt cosas giai arabas, unu pagheddu. Custas froriduras donant unu

sabori diversu, prus sardu, antigun, de sa cantada. Ti portu unesempru de una boxi.

Ddoi est unu cantadori de Teulada [Paolo Mura], chi cantendi a mutetus longus puru,

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Paolo Bravi

oltre ca a sa ghitarrina, fait custas froriduras, ca in sa musica, sa ghitarra naraus ac-ciaccatura. Beh, custu ddu fait cun sa boxi, ma praxit meda. Praxit, parit ca si bieus

rapresentaus su gustu nostu est rapresentau cun custa froridura, fait prpiu parti de

sidioma nostu

[tr. from Sardinian (Campidanese): Particularly in su Campidanu and in su Sulcis

[Southern Sardinia], we love making froriduras because they are a kind of an Arabian

thing, somehow. Froriduras give the singing a different flavour, a more Sardinian and

more ancient one. Let me take a voice as an exemple. There is a singer from Teulada

[a village in the south-west coast of Sardinia; the singer is Paolo Mura] who, while

singing either in the a mutetus longus style and in the a sa ghitarrina [with the guitar]

style, makes these froriduras, which in music, on the guitar, we call acciaccatura.

Well, he makes this with his voice, and people appreciate very much. It seems that we

feel represented our taste is represented by this froridura, it is really a part of oursinging idiom [interview to Giovanni Meloni, 10.07.2011]

Vibrato is an aspect of the art of ornamentation which, as opposed to other forms of

embellishments, concerns only the singing voice. A common trend toward a particular style

of vibrato may be seen in all traditional Sardinian singing styles1. Giorgia Loi, a singer with

experience both in popular and Sardinian traditional singing, argues that vibrato is different

in either case:

il vibrato sardo molto pi fitto le onde del vibrato sono molto pi fitte, il vibrato

americano molto pi largo. E poi il vibrato sardo ha dei punti che secondo me non si

definiscono neanche vibrato, adesso mi sfugge il termine, dove c magari un sin-

ghiozzato, ecco, che non viene utilizzato assolutamente nel rock, nel pop

[tr. from Italian: The waves of the Sardinian vibrato are much tighter than those of

the American vibrato. Moreover, the Sardinian vibrato in some points in my opinion

is not really a vibrato, now the word escapes me, there is a sort of hiccup which is

never used in rock or pop music [interview to Giorgia Loi, 12.07.2011]

3. MATERIALS

The object of analysis is a real performance of singing poetry in the traditional style of

Southern Sardinia, namely the a mutetus longus poetical competition which took place in

Terraseo-Narcao (Southern Sardinia) on 7 August 2010, in occasion of the festival in hon-

our of Saint James. The performers were the cantadoris (semi-professionals improvising

and singing poets) Emanuele Saba, Paolo Mura, Antonio Pani, Pierpaolo Falqui (in the fol-

lowing graphs labelled respectively as Sa, Mu. Pa and Fq respectively), with the

vocal accompaniment of Antonio Mei (bsciu, bass voice) and Antonio Garau (contra)(Figure 1). The recording was made with a Tascam DR-100 digital recorder, connected in

line to the mixer of the audio service.

1According to some authors, a rapid fluctuation of the voice with features similar to those

that can be found in the Sardinian traditional song should be defined as tremolo (Brodnitz,

1953; Schoultz-Coulon & Battmer, 1981). In this paper this term will not be used: since it

has also been employed with different meanings (cfr. Lomax, 1968; Schaum, 1982; Giaco-

moni, 1996), it is preferable to avoid it.

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Measurements of vibrato parameters in a performance of Sardinian traditional

singing poetry

Figure 1. On the top: Terraseo-Narcao, 7 August 2010: the public place where the a mute-

tus poetic competition took place. On the bottom: from the left to the right, the four impro-

vising / singing poets: Antonio Pani, Emanuele Saba, Pierpaolo Falqui, Paolo Mura.

The selection of the corpus of vibrato samples has been made through manual segmen-

tation of the recording and performed using the software Praat (Boersma & Weenink,2011). The audio segments included in the corpus have been detected through listening and

exhibit rapid fluctuations of the pitch, with a more or less regular pattern, during the emis-

sion of a vowel.

The identification of vibrato sections in a real performance ofa mutetu singing is not a

straightforward and uncontroversial issue. Two main problems arise.

The first problem concerns the decision of what type of vocal oscillation is to be includ-

ed in the corpus. In same cases, the pitch oscillation is very slight and just hearable (see ex-

ample in Figure 2); in other ones, the distinction between vibrato and wider forms of pitch

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Paolo Bravi

undulation like series of turns(in Italian musical terminology:gruppetto) is not sharp (seeexamples in Figure 3a and 3b). In both cases, the decision whether to consider them as vi-

brato (and therefore include them in the corpus) or not is largely subjective.

Figure 2. Example of light fluctuation of F0.

Figure 3a. Example of clearly recognizable turns: the remarkable extent of the pitch fluctu-ation and the short stops between the downward and upward melodic movements indicate

clear shifts from one degree of the scale to the preceding or the following one.

0 0.2 0.4 0.613

14

15

16

17

18

Semitones(Re=100Hz)

Time (s )

0 0.2 0.4 0.6

14

15

Semiton

es(Re=100Hz)

Time (s )

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singing poetry

Figure 3b. Example of F0 undulation with no clear boundary between vibrato and turns.

The second problem concerns the exact detection of the starting and end points of the

vibrato sections. They are in some cases neither easily to detect by ear nor clearly visible on

the pitch tracking (see example in Figure 4).

Figure 4. Example of vibrato with non clearly defined starting point.

Every segment of vibrato has been labelled by means of a Praat textgrid, with indica-tion of the scale degree and of the vowel used (Figure 5).

0 0.2 0.4 0.6 0.8

14

15

16

17

Semitones(Re=100Hz)

Time (s

)

0 0.2 0.4 0.6 0.8 1 1.2 1.4

8

9

10

Semitones(Re=100Hz)

Time (s )

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Paolo Bravi

The fundamental frequency (F0) tracking was carried out via Praat and the resulting

curves were smoothed by means of the relevant Praatfunction2. In order to obtain reliable

results, the vibrato segments have undergone a two-step filtering process. These prelimi-

nary steps have been performed, as well as the following statistical analysis, by means of

the software R (RDCT, 2011). The first filter has aimed at excluding from the corpus the

segments of very short length. The duration threshold has been arbitrarily set at 0.5 sec. As

a consequence, 162 out of 720 (22%) segments have been filtered out. The second filter has

been applied after a visual inspection of the data and has aimed at a further selection of the

samples by excluding spurious measurements and anomalous values due to inaccuracy in

the procedure of peak detections in the F0 curves. This second step has led to the exclusion

of 52 out of 558 (9%) segments.

The resulting corpus comprises 506 audio segments, whose distribution is unbalanced

across the four singing poets. Almost half of the total number of segments belongs to Paolo

Mura, whereas Pierpaolo Falqui only has only a small number of them (Table 1). Concern-

ing the duration of the audio segments, it is noteworthy that in most cases the length of the

segments is much shorter than that of the excerpts usually employed in the research on vi-

brato (up to 5 / 6 seconds long). In this case, vibrato segments reaching or close to the dura-

tion of 2 seconds occur only exceptionally (overall mean and SD: 0.76 sec. 0.29). Dura-

tions of vibrato segments are different in the four poets (longer in Mura than in the other

poets) and their distribution is positively skewed (again, particularly in the case of Mura;

see Table 1).

2Parameters for pitch tracking have been set as follows: time step: 0.001 s; floor / ceil-

ing: 150 / 300 Hz; remaining parameters: default values (Boersma, 1993). The smoothing

has been applied with parameter bandwidth set to 10 Hz (Praatprocedure for smoothing

pitch tracks is shortly described here: http://uk.groups.yahoo.com/group/praat-

users/message/5529).

Figure 5. An example of manual annotation of the audio file viaPraattextgrid.

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singing poetry

PoetNumber of

collected items

Per-

centage

Duration

Mean SD Q .25 Median Q .75

Fq 35 7 0.72 0.26 0.55 0.65 0.80

Mu 247 49 0.81 0.30 0.59 0.70 0.91

Pa 106 21 0.72 0.24 0.54 0.65 0.76

Sa 118 23 0.70 0.28 0.53 0.61 0.72

Table 1. Number and distribution of durations of samples.

4. ANALYSIS

The features of the vibrato that have been taken into account are rate (VR), extent (VE)

and intonation (MF0). The results of the analysis are synthesized in Table 2 and discussed

in Par. 4.1. Par. 4.2 and Par. 4.3 deals with the effects of vocal timbre, scale degree and du-ration on the aforementioned vibrato features.

Poet VRmn VRsd VEmn VEsd MF0mn MF0sd

Fq 6.36 1.37 0.19 0.06 0.08 0.06

Mu 7.81 0.51 0.26 0.09 0.10 0.07

Pa 7.66 0.44 0.23 0.05 0.10 0.07

Sa 6.05 0.37 0.40 0.09 0.14 0.09

Table 2. Vibrato features per poet: rate (VRmn: mean; VRsd: SD), extent (VE: mean;

VEsd: SD), intonation (MF0mn: mean; MF0sd: SD).

4.1. Vibrato parameters

The typical Sardinian vibrato, as one can hear from Muras or Panis singing voices, hasa high and relatively constant vibrato rate, close to 8 Hz (Table 2 and Figure 6). Sabas vi-

brato is, in this respect, quite different, with a mean rate of 6 Hz, which results higher than

the one observed in most contemporary male opera singers (Large et alii, 1971; Shipp et

alii, 1980) but far from the very high values of Mura and Pani. Falquis vibrato is more a

weak and unstable undulation of voice than a vibrato in the strictest sense of the word, that

is to say a pitch oscillation characterised by a relatively regular periodicity. The main datum

in his case is related to the standard deviation of the vibrato rate. The mean of the SDs is

three times or so higher than those of the other three poets. This means that the rate of the

pitch fluctuation in his case is extremely irregular compared to the others.

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Paolo Bravi

The vibrato extent is usually small. The highest value ( 0.4 st) is shown by Saba, while

the other three poets mean vibrato extent does not reach 0.3 st (Table 2). A relevant fea-

ture is the SD of the values, which is considerably higher in Saba and Mura than in Pani

and Falqui (Table 2 and Figure 7).

The third feature of vibrato which has been taken into account is intonation. Change inintonation has been evaluated referring to the average differential mean (MF0), i. e. by

measuring the absolute difference between the overall F0 mean in the segment and the dy-

namic mean running between pairs of subsequent peaks. In all the four poets mean and SD

are strongly correlated, and the change in intonation is remarkably high, particularly in Sa-

bas vibrato where the mean of the means is 0.14 st and the SD is 0.9 st (Table 2 and Figure

8).

VRsd

VRmn

3

4

5

6

7

8

9

10

11

0 1 2 3 4 5

Fq

0 1 2 3 4 5

Mu

0 1 2 3 4 5

Pa

0 1 2 3 4 5

Sa

Figure 6. Vibrato rate mean (VRmn) and SD (VRsd), per poet.

VEsd

VEmn

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.70.8

0.0 0. 1 0. 2 0.3

Fq

0. 0 0. 1 0. 2 0. 3

Mu

0. 0 0. 1 0. 2 0. 3

Pa

0. 0 0. 1 0. 2 0. 3

Sa

Figure 7. Vibrato extent mean (VEmn) and SD (VEsd), per poet.

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singing poetry

4.2. Vowels and scale degrees

Vibrato rate is generally considered to be constant within a singer. However, some evi-

dence have been put forward that the rate may be affected by the emotional involvement of

the singer (Shipp et alii, 1980), by the age of the singer (Damst et alii, 1982), by the posi-

tion of the vibrato cycle in the vibrato emission (Bretos & Sundberg, 2003). Vibrato extent

has been described as varying with loudness of phonation (Winckel, 1953; Schoultz-Coulon

& Battmer, 1981) and with variation of pitch (Bennett, 1981).

Granted that no previous analysis has been carried out on the vibrato in Sardinian

traditional singing styles, some prospective factors of variation have been tested. In

particular, potential effects due to vocal timbre (vowel) and pitch (scale degree) have been

taken into account and analysed by means of two-way Anova tests, with the followingresults.

Vowel does not have any significant effect on vibrato rate and extent, with the only

exception of Muras vibrato extent (F=3.04, df=4, p=0.017), with [i] significantly higher

than in [a] (Tukey HSD, p=0.003).

Scale degree has a significant effect on the vibrato rate in Mura (F=6.91, df=3,

p=


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Paolo Bravi

the 1, 2 and 3 quartile and by applying one-way Anova tests. The four classes have beenlabelled as L (long), ML (medium long), MS (medium short), S (short).

As Figure 9 shows, duration affects the results in various ways. As far as SD is

concerned, a common trend in the three parameters emerges. Deviation is significantly

higher (or near to the significance level, set at 0.05, in the case of the parameter MF0) in

longer segments. As far as mean is concerned, conversely, opposite trends emerge in the

vibrato rate and extent. Whereas in the former a rise (near to the significance level) is

present in longer segments, in the latter a significant rise (F=6.63, df=3, p


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singing poetry

As far as factors that can account for the vibrato rate and extent variability within eachsinger are concerned, vocal timbre (i.e. singing on different vowels) and pitch (i.e. singing

on different scale degrees) have been first tested. Vocal timbre does not seem to be a valid

explaining factor: only in one case the difference of vowels gives rise to a significant dif-

ference in the rate means. Scale degree seems to have a greater importance, at least in two

poets out of four. In particular, in these two poets a notable difference between low degrees

and high degrees has been noticed in the vibrato extent. Finally, segment duration is a fac-

tor that affects the results, particularly the mean values of the vibrato extent, which are low-

er in longer segments, and the standard deviation in all features (rate, extent and intona-

tion), which is higher in longer segments.

ACKNOWLEDGEMENTS

The author wishes to thank Antonio Pani, Emanuele Saba, Paolo Mura and PierpaoloFalqui, the poets who took part in the performance of Terraseo on 7 August 2010, Antonio

Dess, Carlo Schirru, Giorgia Loi, Giovanni Meloni, Ivo Murgia, Paolo Zedda and the

anonymous reviewers for their cooperation and help.

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