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http://dx.doi.org/10.7776/ASK.2012.31.7.427

A Fast Normalized Cross-Correlation Computation for WSOLA-based Speech Time-Scale Modification  

Lim, Sangjun (Department of Electronics Eng., Pusan National University)
Kim, Hyung Soon (Department of Electronics Eng., Pusan National University)
Publication Information
The Journal of the Acoustical Society of Korea / v.31, no.7, 2012 , pp. 427-434 More about this Journal
Abstract
The overlap-add technique based on waveform similarity (WSOLA) method is known to be an efficient high-quality algorithm for time scaling of speech signal. The computational load of WSOLA is concentrated on the repeated normalized cross-correlation (NCC) calculation to evaluate the similarity between two signal waveforms. To reduce the computational complexity of WSOLA, this paper proposes a fast NCC computation method, in which NCC is obtained through pre-calculated sum tables to eliminate redundancy of repeated NCC calculations in the adjacent regions. While the denominator part of NCC has much redundancy irrespective of the time-scale factor, the numerator part of NCC has less redundancy and the amount of redundancy is dependent on both the time-scale factor and optimal shift value, thereby requiring more sophisticated algorithm for fast computation. The simulation results show that the proposed method reduces about 40%, 47% and 52% of the WSOLA execution time for the time-scale compression, 2 and 3 times time-scale expansions, respectively, while maintaining exactly the same speech quality of the conventional WSOLA.
Keywords
Time-scale modification; WSOLA; Fast normalized cross-correlation computation;
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