Learning to Align Polyphonic Music. Slide 1 Learning to Align Polyphonic Music Shai Shalev-Shwartz Hebrew University, Jerusalem Joint work with Yoram Singer, Google Inc. Joseph Keshet, Hebrew University

Learning to Align Polyphonic Music. Slide 2 Motivation Symbolic representation: Acoustic representation: Two ways for representing music

Learning to Align Polyphonic Music. Slide 3 Symbolic Representation time pitch - pitch symbolic representation: - start-time

Learning to Align Polyphonic Music. Slide 4 Acoustic Representation Feature Extraction (e.g. Spectral Analysis) acoustic representation: acoustic signal:

Learning to Align Polyphonic Music. Slide 5 The Alignment Problem Setting time pitch actual start-time:

Learning to Align Polyphonic Music. Slide 6 The Alignment Problem Setting Goal: learn an alignment function alignment function actual start-times acoustic representation - pitch symbolic representation - start-times

Learning to Align Polyphonic Music. Slide 7 Previous Work Dynamic Programming (rule based) Dannenberg 1984 Soulez et al Orio & Schwarz 2001 Generative Approaches Raphael 1999 Durey & Clements 2001 Shalev-Shwartz et al. 2002

Learning to Align Polyphonic Music. Slide 8 Our Solution Discriminative Learning Algorithm Training Set Alignment function Discriminative Learning from examples

Learning to Align Polyphonic Music. Slide 9 Why Discriminative Learning? “ When Solving a given problem, try to avoid a more general problem as an intermediate step ” (Vladimir Vapnik’s principle for solving problems using a restricted amount of information) Or, if you would like to visit Barcelona, buy a ticket ! Don’t waste so much time on writing a paper for ISMIR 2004 …

Learning to Align Polyphonic Music. Slide 10 Outline of Solution 1.Define a quantitative assessment of alignments 2.Define a hypotheses class - what is the form of our alignment functions : a.Map all possible alignments into vectors in an abstract vector-space b.Find a projection in the vector-space which ranks alignments according to their quality 3.Suggest a learning algorithm

Learning to Align Polyphonic Music. Slide 11 Assessing alignments e.g.

Learning to Align Polyphonic Music. Slide 12 Feature Functions for Alignment feature function for alignment Assessing the quality of a suggested alignment acoustic and symbolic representation suggested alignment (actual start-times) e.g.

Learning to Align Polyphonic Music. Slide 13 Feature Functions for Alignment correct alignment slightly incorrect alignment grossly incorrect alignment Mapping all possible alignments into a vector space

Learning to Align Polyphonic Music. Slide 14 Main Solution Principle grossly incorrect alignment correct alignment slightly incorrect alignment Find a linear projection that ranks alignments according to their quality

Learning to Align Polyphonic Music. Slide 15 slightly incorrect alignment Main Solution Principle (cont.) An example of projection with low confidence correct alignment grossly incorrect alignment

Learning to Align Polyphonic Music. Slide 16 slightly incorrect alignment Main Solution Principle (cont.) An example of incorrect projection correct alignment grossly incorrect alignment

Learning to Align Polyphonic Music. Slide 17 Hypotheses class The form of our alignment functions: predict the alignment which attains the highest projection defines the direction of projection

Learning to Align Polyphonic Music. Slide 18 Learning algorithm Optimization Problem: Given a training set : Find: a projection and a maximal confidence scalar such that the data is ranked correctly:

Learning to Align Polyphonic Music. Slide 19 Algorithmic aspects Iterative algorithm: Works on one alignment example at a time The algorithm works in polynomial time although the number of constraints is exponentially large Simple to implement Convergence: Converges to a high confidence solution #iterations depends on the best attainable confidence Generalization: The gap between test and train error decreases with the #examples. The gap is bounded above by

Learning to Align Polyphonic Music. Slide 20 Experimental Results Task: alignment of polyphonic piano music Dataset: 12 musical pieces where sound and MIDI were both recorded + other performances of the same pieces in MIDI format Features: see in the paper Algorithms: Discriminative method Generative method: Generalized Hidden Markov Model (GHMM) Using the same features as in the discriminative method Using different number of Gaussians (1,3,5,7)

Learning to Align Polyphonic Music. Slide 21 Experimental Results (Cont.) Our discriminative method outperforms GHMM GHMM-1 GHMM-3 GHMM-5 GHMM-7 Discriminative Loss (ms)

Learning to Align Polyphonic Music. Slide 22 The End