Dept. for Speech, Music and Hearing

Quarterly Progress andStatus Report

Formant frequencies in choirsingers

Ternstrom, S. and Sundberg, J.

journal: STL-QPSRvolume: 28number: 4year: 1987pages: 043-055

http://www.speech.kth.se/qpsr

STL-QPSR 4 / 1987

B. FORMANT FREQUENCIES I N CHOIR SINGERS

S. Ternstrom & J . Sundberg

A b s t r a c t The f o u r l o w e s t formant f r e q u e n c i e s a r e measured i n e i g h t members

o f t h e b a s s sect i o n o f a g o o d a m a t e u r c h o i r u n d e r t w o c o n d i t i o n s : ( 1 ) when r e a d i n g t h e t e x t o f a pozm a loud ; and ( 2 ) when performing t h e same t e x t a s a song. C e r t a i n fo rmant f requency d i f f e r e n c e s are observed which are s i m i l a r t o t h o s e p r e v i o u s l y f o u n d b e t w e e n p r o f e s s i o n a l s i n g e r s ' spoken a n d sung v o w e l s . The i n t e r s u b j e c t sca t te r o f t h e t h r e e lowest formant f r e q u e n c i e s w a s s m a l l e r r a n d t h e f o u r t h f o r m a n t w a s l o w e r i n s i n g i n g .

I n t r o d u c t i o n A p r i m a r y e s t h e t i c c o n c e r n o f c h o i r s i n g i n g is t h a t i n d i v i d u a l

v o i c e s shou ld n o t b e d i s c e r n i b l e as such. Choir s i n g e r s ars r e q u i r e d t o a c h i e v e a b l e n d o f t h e i r own v o i c e w i t h t h e s o u n d o f t h e rest o f t h e cho i r . I n a g e n e r a l s e n s e , t h i s means t h a t e a c h s i n g e r , i n a d d i t i o n t o performing t h e music , shou ld s t r i v e t o make t h e sound o f h i s o r h e r own

v o i c e similar i n c h a r a c t e r t o t h a t which is p r e v a l e n t i n t h e group. A c o u s t i c a l l y , t h i s m i g h t i m p l y a m a t c h i n g o f l o u d n e s s (Goodwin,

1980) a s w e l l a s o f fo rmant s t r u c t u r e and v o i c e s o u r c e p r o p e r t i e s (Ros- s i n g , S u n d b e r g , & T e r n s t r o m , 1986) . I n o r d e r t o e x p l a i n why a c h o i r sounds t h e way i t d o e s , w e c l e a r l y r e q u i r e k n o w l e d g e o f t h e v o c a l be-

h a v i o r o f t h e s i n g e r s . The p r e s e n t i n v e s t i g a t i o n compares t h e fo rmant f r e q u e n c i e s i n s p e e c h t o t h o s e i n s i n g i n g , a s o b s e r v e d i n e i g h t b a s s c h o i r s i n g e r s . Comparisons are a l s o made w i t h s o l o s i n g i n g , as measured

i n earlier exper iments .

P r e v i o u s work A f a i r amount o f work on t h e vowel a r t i c u l a t i o n o f s i n g e r s h a s been

r e p o r t e d (e.g., S u n d b e r g , 1974; R o s s i n g & al. , 1986; 1 9 8 7 ) , e s p e c i a l l y concern ing t h e " s i n g e r ' s f o r m a n t " o f p r o f e s s i o n a l o p e r a s i n g e r s .

Sundberg ( 1974) found t h a t p r o f e s s i o n a l s i n g e r s used d i f f e r e n t f o r m a n t s i n s p e e c h a n d i n s i n g i n g . I n p a r t i c u l a r r t h e f i r s t f o r m a n t f r e q u e n c y

w a s f o u n d t o b e h i g h e r i n m o s t sung v o w e l s , a s c o m p a r e d t o s p e e c h . S i m i l a r l y , f o r f r o n t v o w e l s , t h e s e c o n d a n d t h i r d f o r m a n t s w e r e con- s i d e r a b l y l o w e r i n s i n g i n g . F u r t h e r m o r e , p r o f e s s i o n a l s i n g e r s w e r e found to c l u s t e r t h e i r h i g h e r f o r m a n t s r t h e r e b y g e n e r a t i n g t h e s o - c a l l e d

STL-QPSR 4/1987

s inge r ' s fo rman t . The u n u s u a l s p e c t r a l e n e r g y d i s t r i b u t i o n t h u s a- chieved makes t h e v o i c e more p e n e t r a t i n g and makes i t easier f o r t h e s o l o s i n g e r t o b e h e a r d , e.g., o v e r a l o u d o r c h e s t r a .

Cleveland (1976) s tud ied t h e formant f requencies of male s o l o i s t s of d i f f e r e n t v o c a l c l a s s i f i c a t i o n s , i.e., b a s s , bar i t o n e and t e n o r . H e found a s m a l l b u t sys t ema t i c i nc rease i n a l l formants when going from basses t o t e n o r s .

Rossing & al . (1986; 1987) compared s o l i s t i c and c h o r a l modes o f singing. They found t h a t s i n g e r s , who were experienced both a s s o l o i s t s and c h o i r s inge r s , modified t h e i r v o i c e s somewhat when changing from a s o l o t o a c h o i r mode o f s i n g i n g . I n t h e c h o i r mode, t h e s i n g e r ' s formant was less p r o m i n e n t , and t h e a m p l i t u d e o f t h e f u n d a m e n t a l was higher; hence, t h e a r t i c u l a t i o n was c l o s e r t o t h a t of speech.

Goodwin (1980) s tud ied how s i n g e r s behaved when asked t o blend w i t h a c h o i r they heard over earphones. H e found t h a t t h e s u b j e c t s tended t o use a s o f t e r v o i c e l e v e l when b l e n d i n g and t h a t t h e i r h i g h e r s p e c t r u m p a r t i a l s were r e l a t i v e l y weaker, as might be expected, g iven t h e lower voice l eve l . These i n v e s t i g a t i o n s were mainly concerned w i t h t h e per- sona l vo ice t imbre of i nd iv idua l s , being mainly dependent on t h e higher formants. For c h o i r s , w e a l s o need t o add res s t h e i s s u e of vowel qua l i - t y , being mainly determined by t h e two lowes t formants. Thus, w e might a s k how t h e vowels a r e pronounced i n c h o i r s ing ing a s compared t o speech o r s o l o s inging , and whether t h e s i n g e r s i n a c h o i r do t r y t o converge, e.g. I f o r r e a s o n s o f c h o r a l b l e n d , on a p a r t i c u l a r set o f f o r m a n t f r e - quencies f o r a g iven vowel. I f SO, do c h o i r s i n g e r s a d j u s t t o t h e vowel a r t i c u l a t i o n o f t h e ensemble m o m e n t a r i l y , vowe l f o r v o w e l , w h i l e t h e y are s i n g i n g t o g e t h e r , o r g r a d u a l l y , a s a r e s u l t o f l ong- t e rm t r a i n i n g wi th t h e g r o u p , o r b o t h ? I n t h e p r e s e n t e x p e r i m e n t , t h e s u b j e c t s s ang alone, s o t h e r e s u l t s should r e f l e c t on ly t h e long-term t r a in ing .

Sub jec t s I n o r d e r t o s i m p l i f y t h e f o r m a n t measu remen t s , it w a s d e c i d e d t o

use only bas s s i n g e r s , s i n c e t h e i r low fundamental f requencies g i v e rise t o s p e c t r a w i t h c l o s e l y spaced harmonics. Eight s u b j e c t s p a r t i c i p a t e d , who had been s i n g i n g i n t h e same c h o i r f o r s e v e r a l y e a r s ( a l t h o u g h n o t a l l of them a t t h e same time). A l l were long-time r e s i d e n t s o f Stock- holm, and had f a i r l y s i m i l a r Stockholm d i a l e c t s i n normal speech.

Met hod The s u b j e c t s were recorded one a t a time. F i r s t , t h e s u b j e c t spoke

t h e t e x t o f a song p h r a s e f o u r t i m e s , and t h e n sang i t f o u r times i n accordance w i t h t h e s c o r e us ing t h e c o r r e c t key. The r e c o r d i n g s were made i n a n a n e c h o i c room. The s i g n a l s f rom a no rma l microphone and a

STL-QPSR 4 / 1987

Resu l t s

The r e p r o d u c i b i l i t y of t h e d a t a was checked by comparing two ver-

s i o n s of t h e same vowel, /o/, which occurred both near t h e beginning and near t h e end o f t h e ph rase . T a b l e I shows t h e f o r m a n t f r e q u e n c y a v e r - ages a c r o s s s u b j e c t s f o r t h e f i r s t and second t i m e when t h e vowe l oc- cur red d u r i n g t h e s u b j e c t s ' r e a d i n g and s i n g i n g o f t h e t e x t . A s c a n b e seen i n t h e t a b l e , t h e d i f f e r e n c e s are m e r e l y small f r a c t i o n s o f t h e s tandard d e v i a t i o n s , s o t h e r e were no s i g n i f i c a n t d i f f e r e n c e s i n t h e formant frequency averages between t h e f i r s t and second occurrences (see Table I).

Table I. Formant frequency averages and s tandard d e v i a t i o n s of t h e d u p l i c a t e vowel /o// f i r s t and second t i m e it occurred i n t h e t ex t s . P o p u l a t i o n s i z e = 8.

SPEECH SINGING mean SD mean SD

(Hz) (Hz) (Hz) (Hz) F1 F i r s t 396 38 396 32

Second 394 24 395 17 Difference -2 - 1

F2 F i r s t 741 57 767 52 Second 731 74 774 44 Difference - 10 7

F3 F i r s t 2447 192 2349 9 1 Second 2530 172 2406 149 Dif fe rence 8 3 57

F4 F i r s t 3178 68 2975 192 Second 3108 209 3019 201 Difference -70 44

Typical d i f f e r e n c e s were found i n t h e mean formant frequencies. Our averages and s t a n d a r d d e v i a t i o n s f o r t h e f i r s t two f o r m a n t s o f t h e e n t i r e se t o f v o w e l s are p l o t t e d t o g e t h e r w i t h o t h e r p r e v i o u s l y pub- l i s h e d , c o m p a r a b l e d a t a i n Fig. 3 i n terms o f f o r m a n t c h a r t s . I n o u r sub jec t s , t h e means o f t h e f i r s t and second f o r m a n t s were s h i f t e d i n s ing ing toward t h e c e n t e r of t h e vowel t r i a n g l e , i.e., t h e vowels were somewhat n e u t r a l i zed.

In a previous inves t iga t ion , a s i m i l a r comparison w a s made f o r four p ro fe s s iona l b a s s and b a r i t o n e s i n g e r s i n a CVC c o n t e x t (Sundberg , 1970). Only t h e four vowels t h a t occurred a l s o i n our experiment were

Fig. 3. Mean F1 and F2 (kHz) in speech and singing for (a) eight choir singer subjects, and (b) four professional singers as measured by Sundberg in 1970. Fig. 3c shows data from Rossing 6 al. (1986) comparing choir and solo modes of singing. In (a), the standard deviations in F1 and F2 are shown as ellipses. Arrows in the figure indicate the change from speech to singing.

STL-QPSR 4 j 1987

shown. A s can b e s e e n i n Fig. 3b, t h e r e s u l t s a r e similar. The second formant was lowered i n t h e v o w e l s /i/ and / a e / , w h i l e t h e r e were no c l e a r changes i n the vowels /o/ and /6/ . Thus, chora l and s o l o s i n g e r s seem t o change t h e i r lower formants s i m i l a r l y when switching to singing from speech.

Fig. 3c I showing d a t a from Rossing & a 1 (1986) , compares f i v e singers' s o l o and c h o r a l s ing ing . I n t h i s c a s e , no s y s t e m a t i c d i f f e r - ences i n F1 o r F2 are apparent. We might therefore i n f e r t h a t r although speech and singing d i f f e r , s inging is much the same a s s o l o singing, a s regards the f i r s t two formants.

Fig. 4 p r e s e n t s t h e co r respond ing d a t a r e g a r d i n g F3 and F4. For the choi r s ingers , it can be seen t h a t the mean F3 was lower i n s inging, except f o r t h e vowel /ae/ . Also1 F4 was c l o s e t o 3 kHz i n a l l sung vowelsr e x c e p t / a / and /E/ which, i n t e r e s t i n g l y , were t h e o n l y two vowels t h a t appeared i n unstressed pos i t ions i n the music. In profes- s iona l s inger s (dash-dotted l i n e s ) , both F3 and F4 seem t o be f a i r l y low a l ready i n speech; still, some reduction of F4 can be seen here a s w e l l .

I I I I I I I I I I I I I -

AVERAGE OF SO

- -

- P

- - i ld' - - k - - -

I I I I I I I I I I I I I 1 I

F3 ( k H z )

1 . 4 Vowel averages of F3 and F4 in speech (oj and singing ( 0 ) . Each point represents the mean of e lgh t subjec ts . For c l a r i t y , only the average standard deviat ions a r e shown (box) . Data from four profess ional s ingers (Sundberg, 1970) a r e shown f o r comparison (dash-dotted l i n e s ) .

i Y

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While t h e two lowes t formants d e f i n e vowel q u a l i t y a lmos t e n t i r e -

l y , t h e h i g h e r f o r m a n t s a r e more s i g n i f i c a n t t o t h e p e r s o n a l v o i c e timbre. For t h i s r e a s o n , a v e r a g e s o f t h e h i g h e r f o r m a n t s were a l so c a l c u l a t e d p e r s u b j e c t (F ig . 5). I n s i n g i n g , a l l s u b j e c t s b u t o n e low-

e r e d both t h e i r mean F4 and, t o a lesser e x t e n t , also F3. I I I 1 I I I I I I I

- AVERAGE OF SO - - - - -

'? i -

I I I I I I I I 1 I I .

Fig . 5 . Subjec t averages of F3 and F3 i n speech (n) and s ing ing (0). Each p o i n t r e p r e s e n t s t h e mean of n ine vowels. For c l a r i t y , on ly t h e average s tandard dev ia t i ons a r e shown (box) .

An i n t e r e s t i n g a s p e c t o f f o r m a n t s number 3 , 4 , and 5 is t h e s i n g - er's formant which seems a s s o c i a t e d w i t h a c l u s t e r i n g o f t h e s e formants

(Sundberg, 1974). T h e r e f o r e , t h e p r o x i m i t y o f F3 t o F5 or t o F4 c a n b e used a s a p e r t i n e n t measure. I n many s p e c t r o g r a m s , t h e f i f t h f o r m a n t was hard to i d e n t i f y and measure and w a s t h e r e f o r e no t included i n t h e i nves t i ga t ion . Fig. 6a shows a correlogram of t h e d i f f e r e n c e F4-F3 f o r

speech and s i n g i n g f o r a l l v o w e l s and s u b j e c t s . The re is o n l y a weak

tendency toward a s m a l l e r d i f f e r e n c e i n s inging. The corresponding d a t a from Sundberg (1970) i n Fig. 6b show a much clearer d i f f e r e n c e between speech and s ing ing f o r p ro fe s s iona l s ingers . These r e s u l t s s q g e s t t h a t t h e c h o i r s i n g e r s u b j e c t s , u n l i k e t h e p r o f e s s i o n a l s r have a s imilar l e v e l o f t h e i r h i g h e r f o r m a n t s when t h e y s i n g a s when t h e y speak. I n o t h e r words, a prominent s inger ' s formant appears t o be t h e s o l o s ing- er's c h a r a c t e r i s t i c .

STL-QPSR 4/1987 - 50 -

EIGHT CHOIR SINGERS 1.4

FOUR PROFESSIONAL SOLO SINGERS

F 4 - F3 IN SPEECH [ k H z ]

Fig 6. Correlograms of the difference F4-F3 for all tokens; (a) results from choir singers in the present experiment, (b) data from pro- fessional solo singers (Sundberg, 1970).

STL-QPSR 4/:1987

The long-term-average spectrum (LTAS) l e v e l d i f f e r e n c e between t h e 3000 Hz and 500 Hz b a n d s is a more d i r e c t i n d i c a t o r o f t h e l e v e l o f t h e s i n g e r ' s f o r m a n t (Ross ing & a l . , 1986) . T h e r e f o r e , LTAS w e r e made o f t h e e n t i r e material. The l e v e l o f t h e 3 kHz band showed on ly a moderate r e l a t i v e i n c r e a s e (mean = 1.4 dB) i n s i n g i n g a s compared t o speech . Th i s change c o u l d b e a s c r i b e d t o t h e a v e r a g e 7.2 dB i n c r e a s e o f SPL

observed i n t h e sung c a s e ; i t is w e l l known t h a t SPL i n c r e a s e s are accompanied b y a r e d u c t i o n o f t h e o v e r a l l s p e c t r u m t i l t ( F a n t , 1959; Sundberg , Ternstrom, Perk ins , & Gramming , 1986).

The ques t i on now is whether or n o t t h e s u b j e c t s agreed more c l o s e l y amongst e a c h o t h e r on t h e f o r m a n t f r e q u e n c y v a l u e s i n s i n g i n g as com- pared t o s p e e c h , i-e., i f t h e y t u n e d t h e i r f o r m a n t f r e q u e n c i e s t o a p a t t e r n common t o t h e g r o u p members. I n o r d e r t o i n v e s t i g a t e t h i s , w e adopted t h e s tandard d e v i a t i o n s f o r t h e formant f r equenc i e s as a s c a t t e r measure a l lowing u s t o ana lyze t h e formant scatter a c r o s s subjec ts . Fig. 7 shows a c o r r e l o g r a m o f t h e s t a n d a r d d e v i a t i o n s a c r o s s s u b j e c t s f o r formants 1-41 compar ing spoken and sung vowe l s . S i n c e t h e s t a n d a r d d e v i a t i o n s are shown i n Hz, g r e a t e r v a l u e s are t o b e e x p e c t e d f o r t h e h igher formants. Expressed i n percent t h e s t anda rd d e v i a t i o n s were i n t h e r a n g e o f 5-10% f o r a l l f o u r f o r m a n t s . I t c a n b e s e e n t h a t t h e s t anda rd d e v i a t i o n s o f formants 1-3 were g e n e r a l l y s m a l l e r i n singing. Using a t-test f o r p a i r w i s e dependent measures, w i t h t h e SD v a l u e s as primary d a t a , t h e S D o f f o r m a n t s 1, 2, and 3 poo led was found t o b e s i g n i f i c a n t l y lower ( ~ ~ 0 . 0 1 ) i n s i n g i n g . T h i s s u p p o r t s t h e h y p o t h e s i s t h a t t h e s u b j e c t s tuned t h e i r lower formants f o r t h e v a r i o u s vowels to p a t t e r n s common f o r t h e group.

It is i n t e r e s t i n g t h a t , a c c o r d i n g t o Fig. 5 , a l l s u b j e c t s l o w e r e d t h e i r F4 i n s i n g i n g , w h i l e a c c o r d i n g t o Fig. 7 , t h e S D i n F4 a c r o s s s u b j e c t s r e m a i n e d t h e same i n s i n g i n g . T h i s s u g g e s t s t h a t w i t h i n s u b j e c t s , F4 was changed s y s t e m a t i c a l l y f o r s i n g i n g , t h o u g h t o v a l u e s t h a t d i f f e r e d b e t w e e n s u b j e c t s t s u c h t h a t t h e S D was u n a f f e c t e d when computed o v e r s u b j e c t s . Given t h e d i f f e r e n c e s b e t w e e n i n d i v i d u a l s , it seemed p e r t i n e n t t o c a l c u l a t e a l s o t h e f o r m a n t s c a t t e r a c r o s s v o w e l s (Fig. 8 ) . By and l a r g e , t h i s s c a t t e r is h i g h e r t h a n t h e scatter a c r o s s s u b j e c t s , s i n c e d i f f e r e n t vowels are being pooled w i t h each other . We no te t h a t t h e SD's i n F1 and F21 b e i n g m a i n l y d e t e r m i n e d by t h e set o f vowels used, a r e f a i r l y independent of sub jec ts . Th i s e x p l a i n s t h e c l o s e grouping o f t h e p o i n t s f o r F1 and F2. Moreover, t h e SD v a l u e s f o r F1 and F2 were s l i g h t l y lower i n s ing ing a l s o across vowels , cf.1 Fig. 3a. The SD i n F3 and F4 are less vowe l d e p e n d e n t and more p e r s o n a l , and show markedly lower scatter i n t h e sung case. S ince t h e scatter i n F4 a c r o s s s u b j e c t s w a s unchanged i n s ing ing , it would seem t h a t each c h o i r s i n g e r s u b j e c t has a s y s t e m a t i c bu t persona l way o f pu t t i ng F4 i n t o a "singing" mode. To a lesser e x t e n t , t h i s might hold also f o r F3.

-

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S.D. in Fn for spoken vowels [ log Hz1

F i g . 7 . S tandard d e v i a t i o n s acrodd e i g h t s u b j e c t s ( l o g Hz) -in F1, F2, F3, and F4 i n spoken and sung vowels.

S.D. in Fn in speech [ log Hz ]

Fig . 8. S tandard d e v i a t i o n s a c r o s s n i n e vowels ( l o g Hz) i n F1, F2, F3, and F4 f o r t h e e i g h t s u b j e c t s i n speech and s i n g i n g .

STL-QPSR 4 / 1987 - 54 -

a s barbershop q u a r t e t s , s i m i l a r spectrum envelopes should maximize beat- ing i n m i s t u n e d c o n s o n a n t i n t e r v a l s ; i n t h a t c a s e , t h e a m p l i t u d e s o f t h e common p a r t i a l s are more l i k e l y t o match. T h i s m i g h t g i v e t h e s i n g e r s b e t t e r a u d i t o r y c u e s t o t h e c o r r e c t i n t o n a t i o n . I n l a r g e r ensembles, on t h e o t h e r hand, bea t ing must be abundant and probably t o o random t o b e o f a n y u s e i n a i d i n g i n t o n a t i o n . I n c a s e s where a f o r m a n t is p l a c e d on a p a r t i a l t h a t is common t o two s i m u l t a n e o u s l y sound ing tones, a s m a l l s c a t t e r may b e h e l p f u l f o r i n t o n a t i o n ( T e r n s t r o m &

Sundberg , 198 2).

The s inger 's formant is a voice proper ty which usua l ly is acqui red by s o l o i s t t r a i n i n g . Our c h o i r s i n g e r s d i d n o t show a n y p r o m i n e n t s i n g e r ' s formant. In a comparison of s o l o and chora l s ing ing , Rossing &

al. (1986) found a much more p r o m i n e n t s i n g e r ' s f o r m a n t even i n t h e cho ra l mode o f s i n g i n g . However, i n t h a t i n v e s t i g a t i o n , t h e s u b j e c t s were s i n g e r s who pe r fo rmed p r o f e s s i o n a l l y b o t h a s s o l o and as c h o r a l s i n g e r s , and t h e c h o i r s t h e y be longed t o were o f a h i g h p r o f e s s i o n a l standard. T h i s shows t h a t t h e p r e s e n c e o f a s i n g e r ' s f o r m a n t d i f f e r s between choi rs . The present r e s u l t s would be more r e p r e s e n t a t i v e of t h e average a m a t e u r c h o i r s i n g e r . I f SO, it would b e i n a p p r o p r i a t e f o r a s inge r t o s i n g w i t h a s i n g e r ' s f o r m a n t i n a n a m a t e u r c h o i r . Doing SOI

t h i s s i n g e r would f a i l t o blend wi th t h e ensemble sound (cf., SundbergI

1977). On t h e o t h e r hand, i f a l l c h o i r members s i n g w i t h a s i n g e r ' s formant, which might occur i n some opera c h o i r s t t h e blending should not be a f f e c t e d . I n any e v e n t , t h e d e g r e e t o which a s i n g e r ' s f o r m a n t is present i n a c h o r a l sound must b e r e l e v a n t t o t h e t imbre o f t h e c h o r a l sound.

The present i n v e s t i g a t i o n has demonstrated t h a t cho ra l bas s s i n g e r s f o r some reason adopt c e r t a i n vowel formant p a t t e r n s t h a t are d i f f e r e n t from and more u n i f i e d t h a n t h o s e t h e y u s e i n speech . I t r e m a i n s t o b e inves t iga t ed t o what e x t e n t t hese u n i f i e d formant p a t t e r n s are shared a l s o by t h e o t h e r p a r t s o f a c h o i r . Also , it would b e i n t e r e s t i n g t o map t h e formant p a t t e r n s cha rac t e r i z ing d i f f e r e n t t ypes of choirs . In such a s t u d y , it would c e r t a i n l y b e r e w a r d i n g t o complement f o r m a n t frequency measurement by s y n t h e s i s and chora l sounds.

Acknowledgments The p a r t i c i p a t i o n of t h e c h o i r s i n g e r s is g r a t e f u l l y acknowledged.

Our thanks are a l s o extended t o t h e cho ra l d i r e c t o r s Margareta Skoglund and Lars T i l l e n i u s f o r t h e i r a s s i s t ance . This p r o j e c t w a s supported by the Swedish Council f o r Research i n t h e Humanities and Soc ia l Sciences.

STL-QPSR 4/19E7

References Cleveland, T.F. (1976) : "The a c o u s t i c p r o p e r t i e s o f v o i c e t i m b r e t y p e s and t h e i r i m p o r t a n c e i n t h e d e t e r m i n a t i o n o f v o i c e c l a s ~ i f i c a t i o n " ~ d i s s e r t a t i o n , Un ive r s i t y of Southern Ca l i fo rn i a , Los Angeles.

Goodwin, A. (1980) : " A c o u s t i c s t u d y o f i n d i v i d u a l v o i c e s i n c h o r a l blend", J. R e s . i n S i n g i n g - 3:2), pp. 25-36.

Rossing, T.D. , Sundberg I J. , & T e r n s t r o m , S. (1986) : " A c o u s t i c compar i - son o f v o i c e u s e i n s o l o and c h o i r s i n g i n g " , J.Acoust.Soc.Am. - 79:6, pp. 1975-1981.

Rossing , T.D., Sundberg , J. , & T e r n s t r o m , S. ( 1987) : " A c o u s t i c compar i- son of soprano s o l o and c h o i r s inging" , J.Acous~-SOC.A~. - 82:3 t pp. 830- 836.

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Sundberg , J. ( 1977) : "The a c o u s t i c s o f t h e s i n g i n g v o i c e " , S c i e n t i f i c American 236, March, pp. 82-91. - Sundberg, J., T e r n s t r o m , S., P e r k i n s , W.H., & Gramming, P. (1986) : "Long-term average spectrum a n a l y s i s of phonatory e f f e c t s of no i se and f i l t e r e d a u d i t o r y feedback", STL-QPSR 1/1987, pp. 57-80.

Ternstrom, S. & Sundberg , J. (1986) : " A c o u s t i c s o f c h o i r s i n g i n g " pp. 12-22 i n S. T e r n s t r o m (ed.) A c o u s t i c s f o r Cho i r and O r c h e s t r a , Publ . i s sued by t h e Royal Swedish Academy of Music, No. 52, Stockholm.

Ternstrom, S., Sundberg , J., & A. ~ o l l d h (1983) : " A r t i c u l a t o r y pe r - t u r b a t i o n of p i t c h i n s i n g e r s deprived of a u d i t o r y feedback" STL-QPSR 2- 3/1983, pp. 144-155. ( f o r t h c o m i n g i n J S H R ) .