VTLN in the MFCC domain: band-limited versus local interpolation
Ehsan Variani, Thomas K. Schaaf · 2011
We propose a new easy-to-implement method to compute a Lin-ear Transform (LT) to perform Vocal Tract Length Normalization (VTLN) on truncated Mel Frequency Cepstral Coefficients (MFCCs) normally used in distributed speech recognition. The method is based on a Local Interpolation which is independent of the Mel filter design. Local Interpolation (LILT) VTLN is theoretically and experimentally compared to a global scheme based on band-limited interpolation (BLI-VTLN) and the conventional frequency warp-ing scheme (FFT-VTLN). Investigating the interoperability of these methods shows that the performance of LILT-VTLN is on par with FFT-VTLN and BLI-VTLN. Models trained with LILT- and BLI-VTLN performance degrades if FFT-VTLN is used as a front-end. The degradation for LILT-VTLN is slightly less, indicating that it produces models that are a better match for FFT-VTLN. Index Terms — Automatic speech recognition, VTLN, fre-quency warping, linear transform