Perceptual-MVDR based analysis-synthesis of pitch synchronous frames for pitch modification
Rangarao Muralishankar, M. Ravi Shanker, A. G. Ramakrishnan · 2008
In our earlier work [1, 2], we employed minimum variance distortionless response (MVDR) and MVDR Bauer respectively, as spectral estimation techniques in place of modified-linear prediction in Discrete cosine transform (DCT) based pitch modification [3]. As a general extension, we introduce psychoacoustic characteristics to [1, 2] resulting in Perceptual-MVDR (PMVDR) and PMVDR-Bauer algorithms utilized here for spectral estimation. Further, we employ Bauer method of spectral factorization in our later algorithm since it results in causal inverse filter. These are used to obtain residual signal from pitch synchronous speech frames. The residual signal is resampled using DCT/IDCT depending on the target pitch scale factor. Finally, forward filters realized from the above factorization are used to get pitch modified speech. The modified speech is evaluated subjectively by 10 listeners and mean opinion scores (MOS) are evaluated for pitch factors from 0.5 to 2. Modified bark spectral distortion (MBSD) measure is also employed to evaluate objective performance. We found that the proposed approach has been rated with higher MOS and has achieved lower MBSD than the time domain pitch synchronous overlap [4], modified-LP method [3] and MVDR based methods [1, 2]. Further, we modified the pitch contours of 20 affirmative sentences to sound like interrogative sentences, using the current as well as our earlier algorithms and compared their performance.