Music as a Formal Language

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1 Music as a Formal Language Finite-State Automata and Pd Bryan Jurish moocow@ling.uni-potsdam.de Universität Potsdam, Institut für Linguistik, Potsdam, Germany pd convention 2004 / Jurish / Music as a formal language p. 1/19

2 Overview The Big Idea: Music as a Formal Language A Brief Tour of Formal Language Theory Finite-State Machines The pd-gfsm Pd Externals Future Directions Concluding Remarks pd convention 2004 / Jurish / Music as a formal language p. 2/19

3 The Big Idea Music as a formal language Syntactic characterization Generic musical structure Formal languages for music Expressive power Practical requirements Applications Open Questions Cognitive plausibility? Musical language spoken language? pd convention 2004 / Jurish / Music as a formal language p. 3/19

4 Formal Language Theory Alphabets and Strings Finite (terminal) Alphabet Σ = {a 1,..., a n } Free Monoid Σ, (finite strings over Σ) Formal Languages Formal Language L Σ Grammars and Automata Grammar G = V, Σ, P, S generates language L = L(G) by production rules α β P Automaton M = Q, Σ, Γ, δ, q 0, F recognizes language L = L(M) by transition rules δ pd convention 2004 / Jurish / Music as a formal language p. 4/19

5 Chomsky Inclusion Hierarchy Turing Machines Linear Bounded Turing Machines Pushdown Automata Finite-State Automata Type-0 { w, M w L(M)} Type-1 {ww w Σ } Type-2 {a n b n n } Type-3 {a n n } Rule Grammars Context-Sensitive Grammars Context-Free Grammars Regular Grammars pd convention 2004 / Jurish / Music as a formal language p. 5/19

6 Musical Structure Tone Dependencies Context-Free Non-Context-Free Musical Languages ML CFL pd convention 2004 / Jurish / Music as a formal language p. 6/19

7 Context-Sensitive Languages Indexed Languages (IL) {a 2n n } Type-1 (CSL) {a n! n } MCSL Convergent MCSLs (T AL = LIL = HL = CCL) {a n b n c n d n n } Type-2 (CF L) {a p p prime } Linear CF Rewrite Languages (LCF RL) {www w a Dyck word} pd convention 2004 / Jurish / Music as a formal language p. 7/19

8 Practical Considerations Improvisation Property Flexibility Mutability Given a valid prefix v Σ of a word vw L, it is decidable in constant time for each a Σ whether there is a w Σ such that vaw L. Amounts to incremental computability. Minimize requirements on what might constitute musical structure. Enable efficient runtime change of language structure. pd convention 2004 / Jurish / Music as a formal language p. 8/19

9 Finite-State Machines Finite-State Acceptor (FSA) A = Q, Σ, δ, q 0, F Q a finite set of states, Σ a finite terminal alphabet, δ : Q Σ 2 Q a finite transition function, q 0 a distinguished initial state, and F Q a set of final states. Rooted directed graph with edge labels in Σ. Finite-State Transducer (FST) M = Q, Σ, Γ, δ, q 0, F Basically an FSA with edge labels in Σ Γ. Weighted FSMs Extend δ by marking each arc with a weight w. pd convention 2004 / Jurish / Music as a formal language p. 9/19

10 Finite State Machines: Example A Recognizer for Simple Cadences IV/1 I/1 0 1 V/1 V/0.3 IV/ pd convention 2004 / Jurish / Music as a formal language p. 10/19

11 Finite State Machines: Applications Markov Chains weighted FSAs incremental stochastic sequence generation Hidden Markov Models weighted FSTs runtime quantization and classification Rational Transformations control message rewrite rules Regular Expressions user-interface specifications pd convention 2004 / Jurish / Music as a formal language p. 11/19

12 The pd-gfsm Library gfsm alphabet NAME Maps Pd atoms integer labels AT&T text format I/O gfsm automaton NAME Weighted finite-state transducer AT&T text and native binary format I/O Suitable for large machines ( 3 million states) gfsm state NAME STATE ID Holds current state for incremental processing gfsm markov NAME Trainable Markov chain patch pd convention 2004 / Jurish / Music as a formal language p. 12/19

13 gfsm markov Example 1 Simple 12-Bar Blues C, F, C, C, F, F, C, C, G, F, C, G, C symbol add $1 gfsm_markov m1 0 C:-/2 C:-/1 0 C G:-/2 C:-/1 G F:-/2 C:-/3 F:-/1 F:-/1 F pd convention 2004 / Jurish / Music as a formal language p. 13/19

14 gfsm markov Example 2 12-Bar Blues with upper duration labels C 1, F 1, C 2, F 2, C 2, G 1, F 1, C 1, G 1, C 1 any2list add $1 $2 gfsm_markov m1 0 G:1/2 C:1/1 G F:1/1 C:1/1 0 C F:2/1 F:1/1 C:1/1 C:2/2 F pd convention 2004 / Jurish / Music as a formal language p. 14/19

15 gfsm markov Example 3 12-Bar Blues with complex state labels C.1, F.1, C.2, F.2, C.2, G.1, F.1, C.1, G.1, C.1 symbol add $1 gfsm_markov m1 0 C.1:-/1 0 C.1 G.1:-/1 C.1:-/1 G.1 F.1:-/1 C.1:-/1 F.1:-/1 G.1:-/1 F.1 C.2:-/1 C.2 F.2:-/1 C.2:-/1 F.2 pd convention 2004 / Jurish / Music as a formal language p. 15/19

16 Future Directions FSM Operations Algebra: compose, intersect, remove-ε Continuous FSMs Threading Compilers & Interfaces Regular Expressions 2-Level Rules Graphical Editor Stochastic Modelling Viterbi Algorithm Baum-Welch Re-estimation pd convention 2004 / Jurish / Music as a formal language p. 16/19

17 Concluding Remarks Expressive Power RL CFL ML MCSL PDL = T L Practical Considerations Improvisability Flexibility Mutability Embedded Implementation pd-gfsm FSMs (weak) in Pd (strong) Best of both worlds pd convention 2004 / Jurish / Music as a formal language p. 17/19

18 The End pd convention 2004 / Jurish / Music as a formal language p. 18/19

19 Mild Context-Sensitivity For every mildly context-sensitive L MCSL: Contstant Growth There is a fixed upper bound j on the minimum length difference between two words of L. Intuition: j length of a measure. Polynomial Parsing Time w? L is decidable in O( w k ) time for some k. Too weak? Improvisation property Bounded Cross-Serial Dependencies There is an upper bound m on the number of cross-serial structural dependencies exhibited by words of L. Too strong? Theme and Variation pd convention 2004 / Jurish / Music as a formal language p. 19/19

ECS 120: Theory of Computation UC Davis Phillip Rogaway February 16, Midterm Exam

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