Algorithms for pattern discovery and pitch spelling in music

Algorithms for pattern discovery and pitch spelling in music

Music Processing Algorithms David Meredith Recent projects Musical pattern matching and discovery Finding occurrences of a query pattern in a work Finding works that are similar to a query work Discovering themes in a work Pitch spelling Predicting the pitch names (e.g., ) of notes in a piano-roll representation (e.g., MIDI) Algorithms for pattern

matching and pattern discovery in music Uses of musical pattern discovery algorithms In content-based music retrieval Creating an index of memorable patterns to enable faster retrieval For music analysts, performers and listeners A motivic/thematic analysis can assist understanding and appreciation In transcription

Helps with inferring beat and metrical structure similar patterns have similar metrical structure Helps with inferring grouping and phrasing parallellism (Lerdahl and Jackendoff, 1983) most important factor in grouping In composition and improvisation Cure composers block by suggesting new material based on patterns discovered in music already written Automatically create new music that develops Importance of repeated patterns in music analysis and cognition Schenker (1954. p.5):

repetition is the basis of music as an art Bent and Drabkin (1987, p.5): the central act in all forms of music analysis is the test for identity Lerdahl and Jackendoff (1983, p.52): the importance of parallelism [i.e., repetition] in musical structure cannot be overestimated. The more Most musical repetitions are neither perceived nor intended Rachmaninoff, Prelude in C sharp minor, Op.3, No.2, bars 1-6

Interesting musical repetitions are structurally diverse Want to discover all and only interesting repeated patterns i.e., themes and motives Class of interesting repeated patterns is structurally diverse because patterns vary widely in structural characteristics many ways of transforming a musical pattern to give another pattern that is perceived to be a version of it Example of repeated motive

Barber, Sonata for Piano, Op.26, 1st mvt, bars 1-4 Example of thematic transformation J.S.Bach, Contrapunctus VI from Die Kunst der Fuge, bars 1-5 String-based algorithms for discovering musical patterns Most previous approaches assume music represented as strings each string represents a voice or part each symbol represents a note or an interval between two consecutive notes in a voice

Similarity between two patterns measured in terms of edit distance calculated using dynamic programming Problems with the string-based approach Edit distance B is an embellished version of A If both patterns represented as strings each symbol represents pitch of note Problems with stringbased approach Polyphony

If searching polyphonic music and do not know voice to which each note belongs (e.g., MIDI format 0 file); or interested in patterns containing notes from 2 or more voices then combinatorial explosion in number of possible string representations if dont use all possible representations Using multidimensional point sets to represent music (1) Using multidimensional point sets to represent music (2)

SIA - Discovering all maximal translatable patterns (MTPs) Pattern is translatable by vector v in dataset if it can be translated by v to give another pattern in the dataset MTP for a vector v contains all points mapped by v onto other points in the dataset O(kn2 log n) time, O(kn2) space where k is no. of dimensions & n is no. of points O(kn2) average time with hashing SIATEC - Discovering all occurrences of all MTPs Translational Equivalence Class (TEC) is set of all translationally invariant occurrences of a pattern

Absolute running times of SIA and SIATEC SIA and SIATEC implemented in C run on a 500MHz Sparc on 52 datasets 6n3456, 2k5 < 2 mins for SIA to process piece with 3500 notes Need for heuristics to isolate interesting MTPs

2n patterns in a dataset of size n SIA generates < n2/2 patterns => SIA generates small fraction of all patterns in a dataset Many interesting patterns derivable from patterns found by SIA BUT many of the patterns found by SIA are NOT interesting 70,000 patterns found by SIA in Rachmaninoffs Prelude in C# minor probably about 100 are interesting => Need heuristics for isolating interesting patterns in output of Heuristics for

isolating musical themes and motives Cov=6 CR=6/5 Cov=9 CR=9/5 Comp = 1/3 Comp = 2/5 Comp = 2/3 Coverage Number of points covered by occurrences of the pattern Compactness = Number of points in pattern Number of points in region spanned by pattern Compression ratio

Coverage Number of points in pattern + Freq. of occurrence of pattern -1 COSIATEC - Data compression using SIATEC Start Dataset SIATEC List of pairs Print out best pattern, P, and its translators Remove occurrences of P from dataset Is dataset empty? Yes End No Using COSIATEC for finding themes and motives in music

First iteration Second iteration SIAM - Pattern matching using SIA Query pattern Dataset k dimensions n points in dataset m points in query O(knm log(nm)) time O(knm) space O(knm) average time with hashing

Improving SIAM Ukkonen, Lemstrm & Mkinen (2003) Use sweepline-like scanning of the dataset (Bentley and Ottmann, 1979) Generalized to approximate matching of sets of horizontal line-segments However, restricted to 2-dimensional representations (unlike SIA-family) Improved complexity to O(mn log m + n log n + m log m) running time (without hashing) O(m) working space

Implemented as algorithm P2 on C-BRAHMS demo web site Improving SIAM - MSM (Clifford et al., 2006) Finding size of maximal match is 3SUM hard (i.e., O(n2) ) Reduce problem of multi-dimensional point-set matching to 1d binary wildcard matching

Random projection to 1D Length reduction by universal hashing Binary wildcard matching using FFTs Find best match and check in O(m) time exactly how many points match at the location that can be inferred from this match Reduces time complexity to O(n log n) Evaluating MSM: Precision-Recall 11-pt Precision-Recall Curve 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2

0.1 0 0 0.2 0.4 0.6 0.8 1 Recall OMRAS MSM

Compared with OMRAS (Pickens et al., 2003) Test set of 2338 documents, 480 used as queries All score encodings in strict score time Queries had notes deleted, transposed and inserted Evaluating MSM: Running time Run on prefixes of various sizes of first movement of Beethovens 3rd Symphony Each prefix matched against itself Compared with largest common subset algorithm of Ukkonen, Lemstrm and Mkinen (2003) MSM nearly 2 orders of magnitude faster (log scale)

Pitch spelling algorithms Chromatic pitch A pitch spelling algorithm takes this... Time Diatonic pitch ...and computes this Time Why are pitch spelling algorithms useful?

In transcription, for generating a correctly notated score from a MIDI or audio file In content-based music retrieval For representing better the perceived tonal relationships between notes Allows us to find occurrences that sound like the query but contain different chromatic intervals For better understanding the cognitive processes that underlie the perception of tonal music Why is the same sound spelt differently in different contexts?

1 3 2 4 Comparative analysis of pitch spelling algorithms Algorithms analysed, evaluated and (in some cases) improved Longuet-Higgins (1976, 1987, 1993) Cambouropoulos (1996,1998, 2001, 2003) Temperley (2001) Chew and Chen (2003, 2005) Meredith (2003, 2005, 2006)

Test corpus 195972 notes, 216 movements, 8 baroque and classical composers almost exactly equal number of notes Freq MIDI Note number The PS13s1 algorithm Tonic chroma and pitch name class Time Initial pitch name class Ebb Bbb Fb 2 9 4 Cb Gb Db

Ab Eb Bb F C G D A E B F#

C# G# D# A# 11 8 3 10 5 0 7 2 9 4

11 6 1 10 6 1 1 T T1 T 2 T T

1 1 T 1 8 3 Freq MIDI Note number The PS13s1 algorithm Tonic chroma and pitch name class Initial pitch name class Ebb Bbb Fb 2

9 4 Time Cb Gb Db Ab Eb Bb F C G D A

E B F# 11 8 3 10 5 0 7 2

9 4 11 6 6 1 C# G# D# 1 T1 T 1 T T

1 1 T 1 T 2 8 3 A# 10 Evaluation criteria and performance metrics Evaluation criteria

Spelling accuracy - how well an algorithm predicts the pitch names Style dependence - how much spelling accuracy depends on style Performance metrics Note error rate - proportion of notes in corpus spelt incorrectly Style dependence - standard deviation of note error rates over 8 composers Robustness to temporal deviations Best versions of algorithms also run on version of test corpus in which onsets and durations were randomly adjusted To evaluate how well algorithms would work on files generated directly from performances

Results for algorithms that were most accurate over clean corpus Algorithm Clean corpus Noisy corpus NER% SD NER% SD PS13s1x 0.56

0.4 9 0.61 0.54 Temperley* 0.70 1.1 3 3.32 3.91 Chew and Chen+ 0.85 0.3 5 0.99 0.55

Cambouropoulos+ 0.85 0.4 0.93 0.53 Kpre= 10, Kpost= 42 7 *Two-pass, half tempo corpus, without enh. change (MH2PX2) 1.79and 1.7 1.75 1.71 +Longuet-Higgins New optimized versions (CamOpt CCOP01-06) Only when music processed a voice at a 9 time (LH1V) x Future work Further development of SIA family of algorithms

Compare SIA algorithms with methods developed in other more mature fields (e.g., computer vision, graph matching) Improve time complexity of SIA algorithms with techniques such as ones used in MSM Adapt algorithms for approximate matching and scaling (matching at different tempi) Adapt SIA and SIATEC for early pruning of uninteresting patterns Further work on PS13s1 Incorporate PS13s1 into complete MIDI-to-notation transcription system

Incorporate PS13s1 into Sibelius notation software Use PS13s1 for key-tracking and harmonic analysis Use PS13s1 for feature extraction on audio data Web-scale content-based music search engine Query-by-humming: Sound-based browsing Allows users to browse for music that has

similar tempo, rhythm, harmony, melody, timbre, etc. Indexing on Interactive input system that allows user to enter query multiple times and/or adjust displayed interpretation melody, harmony, rhythm, tempo, loudness, timbre,... Crawling iTunes, Amazon, MusicBrainz, MySpace, ... Interactive music systems

Design of interactive musical spaces in which motion is mapped onto sound in interesting ways e.g., experimentation with various different pitch and timbre spaces Design of software and hardware that maximises creativity e.g. instruments and software that can be used by both musically trained and untrained to create interesting music and manipulate it Transcription

From MIDI to notation Requires algorithms for pitch spelling (e.g., PS13s1) key tracking (also PS13s1?) metrical structure analysis (finding the beat) voice analysis quantization of note duration values phrase structure analysis Composition and improvisation Creating templates for new pieces of music by analysing the tonal, rhythmic and thematic structures of corpora of existing works Auto-completion or a composers deblocker

Intelligent algorithmic improvisation system Analyses music already written and suggests ways in which it might be continued Finds salient themes and motives in music already generated Creates new music that manipulat these themes in interesting ways Algorithm for complete stylistic composition Input a set of songs or works to be analysed System composes a new work that has similar

structure to those analysed Open-source objectoriented music processing framework Supports the rapid development and testing of algorithms for analysing, retrieving, recognizing, transcribing, composing and performing music. Classes and interfaces that successfully encapsulate the properties of a musical passage, work or collection of works Supports the operations and transformations that a musician, musicologist, composer, listener or performer might want to carry out on the music.

Systems for corpusbuilding Need large, varied and high quality ground truth test-corpora for testing algorithms in music analysis and music information retrieval Currently such corpora are scarce Need more effective methods for digitizing musical resources such as scores and expert analyses and performances Serious obstacle to progress in MIR and computational musicology

Faster and more reliable systems for creating structured digital encodings from printed scores, recordings Such systems are of value to libraries and other parties (e.g., internet search engines) interested in making such resources available online. SLUT Mange tak! References

Bent, I. and Drabkin, W. (1987) Analysis. Macmillan. Bentley, J. and Ottmann, T. (1979) "Algorithms for reporting and counting geometric intersections". IEEE Transactions on Computers, C(28), 643-647. Clifford, R., Christodoulakis, M., Crawford, T., Meredith, D. and Wiggins, G. A. (2006) "A fast, randomised, maximal subset matching algorithm for document-level music retrieval". In Proceedings of the 7th International Conference on Music Information Retrieval (ISMIR 2006), Victoria, Canada. Hsu, J.-L., Liu, C.-C. and Chen, A. L. B. (1998) "Efficient repeating pattern finding in music databases". In Proceedings of the 1998 ACM 7th International Conference on Information and Knowledge Management, pages 281-288. Lemstrm, K. (2000) String Matching Techniques for Music Retrieval. PhD dissertation, Department of Computer Science, University of Helsinki. Lerdahl, F. and Jackendoff, R. (1983) A Generative Theory of Tonal Music. MIT Press, Cambridge MA. Meredith, D., Lemstrm, K. and Wiggins, G. A. (2002) "Algorithms for discovering

repeated patterns in multidimensional representations of polyphonic music". Journal of New Music Research, 31(4), 321-345. Meredith, D. (2006) "Point-set algorithms for pattern discovery and pattern matching in music". In Content-Based Retrieval, Dagstuhl Seminar Proceedings, 06171. Pickens, J., Bello, J. P., Monti, G., Sandler, M., Crawford, T., Dovey, M. and Byrd, D. (2003) "Polyphonic score retrieval using polyphonic audio queries: A harmonic modeling approach". Journal of New Music Research, 32(2), 223-236. Roland, P.-Y. (1999) "Discovering patterns in musical sequences". Journal of New Music Research, 28(4), 334-350. Schenker, H. (1954) Harmony. University of Chicago Press, London. Ukkonen, E., Lemstrm, K. and Mkinen, V. (2003) "Geometric algorithms for transposition invariant content-based music retrieval" In Proceedings of the Fourth International Conference on Music Information Retrieval (ISMIR 2003), Baltimore.

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