Dept. for Speech, Music and Hearing
Quarterly Progress and Status Report
Performance rules for computer controlled performance of contemporary keyboard music
Friberg, A. and Fryd ´en, L. and Bodin, L-G.
and Sundberg, J.
journal: STL-QPSR volume: 28
number: 4 year: 1987 pages: 079-085
http://www.speech.kth.se/qpsr
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STL-QPSR 4/1987
The p u r p o s e o f t h e p r e s e n t i n v e s t i g a t i o n w a s t o e x p l o r e t h e p o s s i - b i l i t i e s o f u s i n g t h e s e p e r f o r m a n c e r u l e s i n t h e n o v e l f r a m e w o r k o f non- t o n a l m u s i c e i t h e r w r i t t e n t o be p e r f o r m e d b y m u s i c i a n s o r g e n e r a t e d a n d performed b y c o m p u t e r . The p r e s e n c e o f a n u n d s r l y i n g t o n a l h a r m o n y c o n s t i t u t e d a r e q u i r e m e n t f o r t w o o f t h e r u l e s . A s i n much c o n t e m p o r a r y music! h a r m o n y i n t h e t r a d i t i o n a l s e n s e i s m i s s i n g t h e s e r u l e s h a d t o be r e f o r m u l a t e d . Thus, a m o d i f i c a t i o n o f t h e s e r u l e s was r e q u i r e d .
I t c o u l d b e a s s u m e d t h a t t h e r u l e s w o u l d w o r k b e t t e r w i t h m u s i c i n t e n d e d t o be p e r formed by m u s i c i a n s on t r a d i t i o n a l i n s t r u m e n t s ! s i n c e t h e r u l e s were d e v e l o p e d f o r t h i s k i n d o f m u s i c . C o m p u t e r m u s i c ! b y c o n t r a s t , is o f t e n n o t i n t e n d e d t o b e p e r f o r m e d i n t h i s way. T h e r e f o r e ,
it was c o n s i d e r e d i n t e r e s t i n g t o t r y t h e r u l e s o n b o t h t h e s e t y p e s o f music.
R u l e s
A g r o u p o f f i v e r u l e s , a l l w i t h c o n t e x t s c o n s i s t i n g o f a few n o t e s o n l y ! was s e l e c t e d from t h e p e r f o r m a n c e r u l e s y s t e m . I n g e n e r a l t h e s e r u l e s w e r e assumed t o be t h e s t r o n g e s t c a n d i d a t e s f o r t h i s music. They o p e r a t e d o n t h e a m p l i t u d e a n d d u r a t i o n p a r a m e t e r s a n d w e r e ! t h u s , d i - r e c t l y a p p l i c a b l e t o p i a n o performance. I n a d d i t i o n , a s a s u b s t i t u t e f o r t h e r u l e r e f l e c t i n g h a r m o n i c p r o g r e s s i o n s i n t r a d i t i o n a l m u s i c , a new r u l e was f o r m u l a t e d which worked w i t h a LONGER CONTEXT.
A s u b s e t o f e i g h t r u l e s w a s used i n t h e e x p e r i m e n t ;
( 1 ) The s h o r t e r t h e s o £ t e r s h o r t e n s t h e n o t e s i n p r o p o r t i o n t o t h e i r d u r a t i o n .
( 2 ) Tempo i n c r 2 a s e i n a s c e n d i n g m e l o d i c m o t i o n s h o r t e n s n o t e s o c c u r r i n g i n a sequence o f r i s i n g p i t c h i n t e r v a l s . The e f f e c t o f t h e r u l e is t o make t h e s h o r t e n e d n o t e s s o u n d a s i f t h e y aim a t t h e " t a r g e t "
n o t e t e r m i n a t i n g t h e a s c e n d i n g motion.
( 3 ) The s h o r t e r t h e s h o r t e r i n c r e a s e s t h e c o n t r a s t i n d u r a t i o n b y making s h o r t n o t e s r e l a t i v e l y s h o r t e r .
( 4 ) Lengthening o f s h o r t e r n o t e a t h a l v e d d u r a t i o n r e d u c e s t h e c o n t r a s t i n d u r a t i o n i n cases when a s h o r t n o t e i s p r e c e d e d b y a n o t e o f twice its d u r a t i o n and f o l l o w e d by a l o n g e r note.
( 5 ) Lengthening o f e x t r e m e l y s h o r t n o t e s a d d s d u r a t i o n t o v e r y s h o r t n o t e s s u r r o u n d e d b y l o n q e r n o t e s , w h e r e b y t h e p r s c e d i n ~ n o t e i s s h o r t e n e d by t h e same amount.
STL-QPSR 4/1987
( 6 ) Chromatic-charge i s a n e q u i v a l e n t t o t h e m e l o d i c a n d h a r m o n i c c h a r g e p r e v i o u s l y u s e d f o r t o n a l m u s i c . E a c h n o t e i s a s s i g n e d a c h a r g e v a l u e t h a t is i n v e r s e l y p r o p o r t i o n a l t o t h e n o t e ' s c h r o m a t i c d i s t a n c e t o t h e f o l l o w i n g n o t e , i f n e e d e d t r a n s p o s e d t o t h e same o c t a v e . Then, a mean v a l u e f i l t e r i n g w i t h a window c o n t a i n i n g f i v e n o t e s is a p p l i e d . The r e s u l t i n g a v e r a g e is t h e n u s e d f o r i n c r e a s i n g t h e sound l e v e l s a n d d u r a t i o n s o f t h e n o t e s . I n t h i s way, t h e r u l e g e n e r a t e s c r e s c e n d o s and diminuendos.
( 7 ) Micropauses i n l e a p s i n s e r t v e r y s h o r t s i l e n t i n t e r v a l s i n m e l o d i c l e a p s . The d u r a t i o n o f t h e s e m i c r o p a u s e s i s p r o p o r t i o n a l t o t h e w i d t h o f t h e l e a p .
( 8 ) S y n c h r o n i z a t i o n o f v o i c e s a p p l i e s i n c o m p o s i t i o n s c o n t a i n i n g more t h a n o n e v o i c e . The s y n c h r o n i z a t i o n i s a c h i e v e d b y e i t h e r s y n - c h r o n i z i n g a l l n o t e s o c c u r r i n g o n t h e f i r s t b e a t i n e a c h b a r o r , b e t t e r , b y d e v i s i n g a s y n c h r o n i z a t i o n v o i c e , c o n s t i t u t e d b y t h e s h o r t e s t n o t e s which o c c u r s , a t e a c h time, i n t h e s c o r e (Sundberg &
a l l 1 9 9 7 ) . I n a d d i t i o n , a t h r e s h o l d o f 50 msec w a s a p p l i e d f o r a n o t e ' s minimum d u r a t i o n . The d u r a t i o n o f a n o t e m u s t s u r p a s s a minimum d u r a t i o n i n o r d s r t o be p e r c e p t i b l e . T h i s r u l e i s s i m i l a r t o c e r t a i n d u r a t i o n r u l e s used i n s p e e c h s y n t h e s i s ( C a r l s o n , F r i - b e r g , ~ r y d h , G r a n s t r o m , & Sundbergl 1957). Also, a n a m p l i t u d e and d u r a t i o n n o r m a l i z a t i o n p r o c e d u r e was used k e e p i n g t h e a v e r a g e sound l e v e l and t h e t o t a l d u r a t i o n o f t h e p i e c e c o n s t a n t .
These r u l e s were t e s t e d by t h e a u t h o r s on v a r i o u s p i e c e s o f contem- p o r a r y music. For r e a s o n s t o be d i s c u s s e d l a t e r r t h e q u a n t i t i e s by which
t h e r u l e s a f f e c t e d t h e p e r f o r r n a n c z had t o b e i n c r e a s e ? a s c o m p a r e d t o what n o r m a l l y a p p l i e s t o t r a d i t i o n a l m u s i c . The q u a n t i t y o f e a c h r u l e was c h o s e n d e p e n d i n g , among o t h e r t h i n g s , o n t h e c h a r a c t e r o f t h e p i e c e . When t h e r e s u l t i n g p e r f o r m a n c e s seemed m u s i c a l l y a p p r o p r i a t e , a f o r m a l l i s t e n i n g e x p e r i m e n t was c a r r i e d o u t , i n which f i v e s u b j e c t s , a l l work- i n g p r o f e s s i o n a l l y w i t h t h i s k i n d of m u s i c , were a s k e d f o r t h e i r p r e f e r - e n c e .
L i s t e n i n g e x p e r i m e n t
A s m e n t i o n e d a b o v e , we u s e 3 t w o d i f f e r e n t k i n d s o f m u s i c ; m u s i c composed f o r p i a n o and c o m p u t e r - j e n e r a t e d randoin music. Seven e x a m p l e s were s e l e c t e d ( s e e T a b l e I ) .
Random a 1 : ~ o r i t h m s were uszfl f o r composing t h e l a s t f o u r p i e c e s i n t h e T a b l e . I n t h e c o m p o s i t i o n s w i t h q u a n t i z e d d n r z ~ t i n ~ s , o n l y t h r e ? d i f f e r e n t d u r a t i o n s were p e r m i t t e d . I n t h e c o ~ n p c ~ s i t i o n s w i t h non-quan-
t i z e d d u r a t i o n s , a t o t a l o f 2 7 ] i f f e r e n t - J u r = i t i o n s were p e r m i t t e d a n d s e q u e n c e s ,3f vore t h a n t w o not.rs o f t h e same 3 , ~ r a t i o n werz n o t a l l o w s ? .
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Models f o r t h e composing a l g o r i t h m s were t a k e n from a s u r v e y by Dodge &
Jerse ( 1 9 8 5 ) .
P. Boulez: F i r s t e i g h t m e a s u r e s of P i a n o s o n a t a . R Webern: T h i r d p i a n o v a r i a t i o n o p 27
I. Xenakis: E x t r a c t from Herma.
WN+Q: White Noise f r e q u e n c y v a r i a t i o n w i t h +Quantized d u r a t i o n s . CW-Q: White Noise f r e q u e n c y v a r i a t i o n w i t h non-Quantized d u r a t i o n s . PN+Q: P i n k Noise f r e q u e n c y v a r i a t i o n w i t h +Quantized d u r a t i o n s . PN-Q: P i n k Noise f r e q u e n c y v a r i a t i o n w i t h non-Quantized d u r a t i o n s .
T a b l e I. Music e x c e r p t s s e l e c t e d f o r t h e l i s t e n i n g e x p e r i m e n t .
Three d i f f e r e n t s e t u p s f o r t h e q u a n t i t y o f e a c h r u l e were used; one f o r t h e Webern p i e c e l one f o r t h e p i e c e s by Boulez and Xenakis! and one f o r t h e computer g e n e r a t e d melodies. Most o f t h e q u a n t i t i e s o f e a c h r u l e were t h e same i n a l l t h e r u l e s e t u p s . They were a b o u t t w o or f o u r times t h e i r normal v a l u e s p r e v i o u s l y used f o r t r a d i t i o n a l music. The l a r g e s t d i f f e r e n c e b e t w e e n t h e s e t u p s o c c u r r e d i n r u l e 3 ( t h e s h o r t e r l t h e s h o r t e r ) f o r t h e Webern m u s i c w h e r e t h e q u a n t i t y w a s i n c r e a s e d e i g h t times a s compared t o t h e o t h e r s e t u p s .
The m u s i c e x a m p l e s were a r r a n g e d i n p a i r s o n a d i g i t a l t e s t t a p e . I n e a c h p a i r ! t h e s a m e e x c e r p t w a s p l a y e d o n e t i m e w i t h a n d t h e o t h e r t i m e w i t h o u t a p p l i c a t i o n o f t h e r u l e s . The o r d e r o f p a i r s and t h e o r d e r w i t h i n p a i r s w e r e r a n d o m l y s e l e c t e d . The t a s k o f t h e l i s t e n e r s w a s t o select which performance t h e y p r e f e r r e d i n e a c h p a i r . The s u b j e c t s were a s k e d t o p a y a t t e n t i o n t o t h e p e r f o r m a n c e a s a w h o l e a n d t o d i s r e g a r d s i n g l e " b a d " n o t e s .
For t h e p i a n o music e x a m p l e s l it seemed e s s e n t i a l t o use a r e a l i s - t i c sound t h a t was e a s i l y a s s o c i a t e d w i t h a human p e r f o r m e r ! w h i l e f o r t h e n o n - p i a n o e x a m p l e s ! i t a p p e a r e d more l o g i c a l t o u s e a p u r e l y s y n - t h e t i c sound t h a t w a s n o t a s s o c i a t e d w i t h a n y c o n v e n t i o n a l i n s t r u m e n t . T h e r e f o r e l t h e s o u n d u s e d f o r t h e f i r s t f i v e e x c e r p t s w a s t h a t o f a sampled p i a n o a s p r o d u c e d b y a C a s i o FZ1 s a m p l e r . For t h e l a s t f o u r examples! a p u r e l y s y n t h e t i c s o u n d o n a Yamaha FBOl s y n t h e s i z e r w a s used.
The pair-wise comparison w a s p r e f e r r e d l a s i t w a s c o n s i d e r e d essen- t i a l n o t t o r a i s e t o o h i g h d e m a n d s o n t h e s u b j e c t s ; a t e s t w h e r e t h e m u s i c a l e x a m p l e s a p p e a r e d i n a t o t a l l y random o r d e r a n d w h a r e t h e s u b j e c t s a s s e s s e d t h e m u s i c a l q u a l i t y o f t h e performance would be more demanding.
The s u b j e c t s w e r e two p r o f e s s i o n a l p i a n i s t s s p e c i a l i z e d on perform- a n c e o f c o n t e m p o r a r y m u s i c ! a n d t h r e e c o m p o s e r s o f e l e c t r o - a c o u s t i c
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music. T h e y f o u n d t h e t a s k f a i r l y s i m p l e s i n c e , i n m o s t cases, t h e y r e a d i l y h e a r d a d i f f e r e n c e b e t w e e n t h e t w o p e r f o r m a n c e s .
R e s u l t s
PIANO SOUND WITH RULES WITHOUT RULES
Webern 4 1
B o u l e z 4 1
X e n a k i s 4 1
WN-Q 5 0
PN-Q 5 0
SYNTHESIZER SOUND
WN-Q 5
PN-Q 4
WN+Q 5
PN+Q 5
T a b l e 11. The number o f s u b j e c t s p r e f e r r i n g t h e v e r s i o n s p l a y e d w i t h or w i t h o u t a p p l i c a t i o n o f t h e r u l e s .
A s c a n b e s e e n f r o m T a b l e I1
,
t h e r e i s a c l e a r p r e f e r e n c e f o r t h e r u l e - g e n e r a t e d p e r f o r m a n c e s i n a l l cases. The p r e f e r e n c e i s s l i g h t l y more e v i d e n t f o r t h e random m e l o d i e s . T h i s is s u r p r i s i n g i n v i e w o f t h e f a c t t h a t t h e r u l e s were d e v e l o p e d f o r m u s i c p l a y e d o n c o n v e n t i o n a l i n s t r u m e n t s .D i s c u s s i o n a n d C o n c l u s i o n s
The p r e s e n t i n v e s t i g a t i o n showed t h a t p e r f o r m a n c e r u l e s d e v e l o p e d f o r t r a d i t i o n a l t o n a l m u s i c improved t h e p e r f o r m a n c e a l s o o f c o n t e m p - r a r y , a t o n a l m u s i c . O n l y f e w r u l e s c o u l d n o t be a p p l i e d f o r v a r i o u s r e a s o n s . The r e v i s i o n s o f t h e r u l e s were small b u t p r o b a b l y i m p o r t a n t .
I n a t o n a l m u s i c , t h e r e a r e n o c h o r d s i n a t r a d i t i o n a l s e n s e . A s a c o n s e q u e n c e , t h e n o t i o n s o f m e l o d i c c h a r g e a n d h a r m o n i c c h a r g e b e c o m e m e a n i n g l e s s . I n a n e a r l y s t a g e , w e t r i e d p e r f o r m a n c e s where t h e m e l o d i c and h a r m o n i c c h a r g e s were s i m p l y o m i t t e d . These p e r f o r m a n c e s seemed t o s u f f e r from a l a c k o f long-term e v e n t s , and t h e m u s i c g a v e t h e impres- s i o n o f a n aimless wandering. A s soon a s t h e c h r o m a t i c c h a r g e was i n t r o - d u c e d , t h i s d i s e a s e was c u r e d . We f i n d i t i n t e r e s t i n g t h a t m u s i c p e r - formance seems t o need e v e n t s e m b r a c i n g , and t h u s marking
,
t h e f o r m a t i o n o f g r e a t e r b l o c k s .I n r a n d o m g e n e r a t e d I ~ U S ~ C , w i d e l e a p s a r e v e r y l i k e l y t o o c c u r , w h i l e l o n g s e q u e n c e s o f s m a l l m e l o d i c i n t e r v a l s are rare. I n t r a d i t i o n a l m u s i c , o n t h e o t h e r h a n d , m e l o d i c m o v e r n e n t s a l o n g t h e s c a l e a r e £ r e - q u e n t . The new r u l e t h a t increased t h e sound l e v e l i n s e q u e n c e s o f small
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i n t e r v a l s may s e r v e t h e p u r p o s e o f m a r k i n g e m p h a s i s , w h i c h w o u l d b e a p p r o p r i a t e ; i n a l l t y p e s o f c o m m u n i c a t i o n i t seems i m p o r t a n t t o e m - p h a s i z e t h e u n e x p e c t e d e l e m e n t s ( C a r l s o n & al., 1987).
Another m o d i f i c a t i o n r e q u i r e d f o r t h i s a p p l i c a t i o n o f t h e r u l e s was t h a t t h e q u a n t i t i e s needed a d j u s t m e n t , a s m e n t i o n e d above. Most o f t h e r u l e s h a d t o be e x a g g e r a t e d i n o r d e r t o p r o d u c e t h e d e s i r e d e f f e c t . Also, i n s o m e cases t h e a m o u n t o f a r u l e h a d t o b e a l t e r e d b e t w e e n d i f f e r e n t p i e c e s . The r e a s o n f o r t h i s is n o t known. However, t h e f o l l o w - i n g e x p l a n a t i o n s seem l i k e l y .
F i r s t , w e u s e d m e r e l y s i x r u l e s w h i l e t h e c o m p l e t e r u l e s y s t e m now c o n t a i n s 1 4 main r u l e s . When i n t r o d u c i n g a new r u l e i n t h e s y s t e m , w e o f t e n o b s e r v e d t h a t a r e d u c t i o n o f t h e q u a n t i t i e s o f t h e e x i s t i n g r u l e s i s n e c e s s a r y i n o r d e r t o a v o i d e x a g g e r a t e d e f f e c t s . A s m a l l number o f r u l e s would t h e n e n t a i l t h e need o f i n c r e a s i n g t h e q u a n t i t i e s o f t h e s e r u l e s .
Second, i t i s p o s s i b l e t h a t c o n t e m p o r a r y m u s i c c a l l s f o r a m o r e o v e r t marking o f m u s i c a l e v e n t s t h a n t r a d i t i o n a l music. For r e a s o n s o f s t y l e , i t w o u l d b e m o r e d i f f i c u l t t o d e t e c t t h e m u s i c a l s t r u c t u r e i n c o n t e m p o r a r y m u s i c t h a n i n t r a d i t i o n a l m u s i c . F o r e x a m p l e , i t w o u l d b e more d i f f i c u l t t o p r e d i c t t h e c o n t i n u a t i o n o f a series o f tones. I t is p o s s i b l e t h a t t h i s l e a d s t o a n e e d f o r i n c r e a s e d q u a n t i t i e s o f t h e r u l e s .
One o f t h e r e a s o n s why t h e r u l e s had a b e t t e r e f f e c t on t h e random m e l o d i e s may be t h a t t h e p i e c e s c o m p o s e d b y a human c o m p o s e r a l r e a d y c o n t a i n s more o f t h e s p e c i a l i n t e r e s t i n g q u a l i t y t h a t p e r f o r m a n c e may enhance. I n a n y e v e n t I a d e a d p a n p e r f o r m a n c e o f t h e h u m a n l y c o m p o s e d p i e c e s seemed more a c c e p t a b l e t h a n when t h e same t y p e o f p e r f o r m a n c e was a p p l i e d t o t h e r a n d o m l y composed p i e c e s .
The p r e s e n t l i s t e n i n g e x p e r i m e n t was c a r r i e d o u t w i t h e x p e r t s o n l y , t h a t i s , c o m p o s e r s a n d p i a n i s t s . A p o s s i b l e q u e s t i o n i s t o w h a t e x t e n t t h e r e s u l t s h o l d t r u e a l s o f o r a t y p i c a l a u d i e n c e a t c o n t e m p o r a r y music c o n c e r t s . Our a s s u m p t i o n is t h a t t h e s e t w o g r o u p s o f l i s t e n e r s d o n o t d i s a g r e e t o a n y g r e a t e r e x t e n t ; f o r e x a m p l e , i t seems i m p o s s i b l e t h a t a s u c c e s s f u l p i a n i s t c o u l d m a i n t a i n i d e a l s n o t s h a r e d by h i s a u d i e n c e . The r e a s o n why we c h o s e e x p e r t s as l i s t e n e r s w a s t o a v o i d t h e g r e a t e r number o f s u b j e c t s .
I n t h e e x p e r i m e n t , w e have shown t h a t t h e r u l e s improved t h e per- formance. On t h e o t h e r h a n d , o u r m e t h o d d o e s n o t a l l o w u s t o c o n c l u d e t h a t o u r r u l e s are o p t i m a l ; f o r i n s t a n c e , w e c a n n o t e x c l u d e t h e p o s s i b i - l i t y t h a t a r a n d o m d i s t r i b u t i o n o f e x p r e s s i v e v a r i a t i o n s w o u l d n o t p r o d u c e a c o m p a r a b l e improvement o f t h e performance. On t h e o t h e r hand, a t a n e a r l y s t a g e d u r i n g t h e development o f t h e r u l e s f o r marking chro- matic c h a r g e , w e t r i e d t o make c r e s c e n d o s w h e r e t h e a v e r a g e c h r o m a t i c c h a r g e i n c r e a s e d . The m u s i c a l e f f e c t of t h i s w a s u n s a t i s f a c t o r y , how- e v e r , and t h e o p p s i t e f o r m u l a t i o n o f t h e r u l e was c l e a r l y p r e f e r a b l e .
