Handle: Engineering Artificial Musical Creativity at the “Trickery” Level - Computational Creativity Research: Towards Creative Machines - page 285

are represented using objects from the sort Recommendation . Simple machinery
for representing affects is achieved using the sort Affect and the predicate symbol
feels . We model affects as a subsort of fluents in the event calculus. The way the
meaning of a music phrase produces an affect is to be captured by translates .
With this syntactic machinery we can account for different agents interpreting
a piece of music differently. What might be the meaning of a musical piece? It
definitely includes affects produced in a listener. In addition to affects, the meaning
can include objective properties of the music, such as its tempo, which the current
version of Handle can process.
The General Problem of Conducting : The general problem of conducting can be
stated as follows: Given a score score and the composer's intention that the listener
listener should feel affect a , is there a music phrase p which is the result of per-
forming score with the conductor's recommendation r such that the meaning of the
phrase p translates into affect a in listener ?

I ( h , t , feels ( listener , a )) ⃒

∃ p : MusicPhrase r : Recommendation .

( B ( h , t , performance ( r , score ) = p ∧ translates ( meaning ( p ), a ))).

What axioms do we need to enable the conductor to determine his actions? At
a minimum, we need a formula specifying combination of the music particles into
music phrases. Axiom A 1 states that two music phrases can combine if and only if

their syntactic types let them combine. If they combine, the combined phrase has
syntax and semantics dictated by the original pieces.

∀ m 1 m 2 : MusicPhrase

allowed ( m 1 , m 2 )

⃔
∃

A 1

m : MusicPhrase . combine ( m 1 , m 2 ) = m

type ( m ) = apply ( type ( m 1 ), type ( m 2 )) ∧

meaning ( m ) = reduce ( meaning ( m 1 ), meaning ( m 2 ))

We need knowledge capturing how the meaning of music translates into affects in
agents. Before formalizing this, we need an axiom stating that musical meanings
produce affects. Axiom A 2 states that if a piece of music has some meaning, there

is an event that causes an affectual response. Here start is a defined function symbol
giving us the start of a music phrase.

∀ m : MusicPhrase ∃ e : Event a : Affect t : Moment

A 2

initiates ( e , a , t ) ∧ translates ( meaning ( m ), a ) ∧ t > start ( m )

Axiom A 3 states a basic property of affects: affects have to be instantiated or asso-

ciated with agents.