Dual-domain Hierarchical Classification of Phonetic Time Series Hossein Hamooni, Abdullah Mueen University of New Mexico Department of Computer Science

What is Phoneme? Phonemes are very small units of intelligible sound (usually less than 200 ms). Phonetic spelling is the sequence of phonemes that a word comprises. Example:  Coat ([ kōt] /K OW T/)  From ([ frəm] /F R AH M/)  impressive ([ imˈpresiv ] /IH M P R EH S IH V/) 2

Phoneme Classification What is phoneme classification?  Input: A short segment of audio signal.  Output: What phoneme it is. Phoneme classification is a complex task:  More than 100 classes (based on International Phonetic Alphabet)  Variation in speakers, dialects, accents, noise in the environment, etc. Phoneme classification can be used in:  Robust speech recognition  Accent/dialect detection  Speech quality scoring 3

Related Work Different methods for phoneme classification have been used in the literature:  Hidden Markov model [Lee, 1989]  Neural network [Schwarz, 2009]  Deep belief network [Mohamed, 2012]  Support vector machine [Salomon, 2001]  Hierarchical methods [Dekel, 2005]  Boltzmann machine [Mohamed, 2010] Although data mining society has shown that k-NN classifiers can work well on time series data, it hasn’t been tried on phoneme yet. 4 [C. Lopes, F. Perdigao, 2011]

Our Dual-domain Approach 5 Time Domain: Using k-NN Dynamic Time Warping (DTW) Expensive Speed up by lower bounding techniques Frequency Domain: Using k-NN Euclidean distance between Mel- frequency cepstrum coefficients (MFCC) Fast

Real Example 6

Challenge 7 DTW is expensive (quadratic in time and space complexity) We need to apply a speed up technique  Solution: Lower bounding techniques w w

DTW Lower bounding 8 Resampling to equal length doesn’t always work !!!

DTW Lower bounding 9  We use the prefix of the longer signal (Prefixed LB_Keogh)  We show that Prefixed LB_Keogh is a lower bound if: w > difference between lengths of two signals  We set w = c * length of the longer signal  We ignore all pairs of signals that don’t satisfy the above condition x Speedup Training Set Size Window Size (c%) Accuracy(%) c = 30%

Data Collection 10  370,000 phonemes are segmented from:  Data is publicly available.

Phoneme Segmentation 11 The Penn Phonetics Lab Forced Aligner (p2fa)  Takes a signal and a transcript  Produces timing segmentations (word level and phoneme level)

Accuracy (All layers) 12  10-fold cross validation  100 random phonemes in each fold

Accented Phoneme Classification x Training Set Size Accuracy MFCC DTW  British vs. American accent  Using Oxford test set  2-class classification problem  No hierarchy

Conclusion  We present a dual-domain hierarchical method for phoneme classification.  We generate a novel dataset of 370,000 phonemes.  We achieve up to 73% accuracy rate for 39 classes.  Our lower bounding technique gives us up to 3X speedup. 14

15 Thank You Data and code available at: