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Bandwidth Extrapolation of Audio Signals

Bandwidth Extrapolation of Audio Signals. Sung-Won Yoon David Choi. February 8 th , 2001. Motivation Proposed system Lapped orthogonal transform (LOT) High frequency regeneration Experiment Expected results Workplan. Outline. Results should be Similar to original wideband signal

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Bandwidth Extrapolation of Audio Signals

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  1. Bandwidth Extrapolation of Audio Signals Sung-Won Yoon David Choi February 8th, 2001 Bandwidth Extrapolation of Audio Signals

  2. Motivation Proposed system Lapped orthogonal transform (LOT) High frequency regeneration Experiment Expected results Workplan Outline Bandwidth Extrapolation of Audio Signals

  3. Results should be Similar to original wideband signal Perceptually better quality X Y Bandwidth Extrapolation X Narrowband LOT coefficients Wideband LOT coefficients nonlinear system Bandwidth Extrapolation of Audio Signals

  4. Proposed System High Frequency Regeneration LOT Narrowband signal Wideband signal LOT-1 LPF 2 LOT Bandwidth Extrapolation of Audio Signals

  5. Lapped Orthogonal TransformH. Malvar & D. Staelin, 1989 2N • Avoids blocking artifact • No increase in bit rate 50% Overlap 2N N LOT coefficient Bandwidth Extrapolation of Audio Signals

  6. Trained system Parameters p are chosen to fit the training data Mapping from narrowband signal to wideband signal Estimate LOT coefficients Magnitude only Y X High Frequency Regeneration From narrowband signal Regenerated high frequency Bandwidth Extrapolation of Audio Signals

  7. Each estimated high frequency coefficient is a weighted combination of the low freq. coefficients Linear Estimation • Possible sparse representation of weights • Weights possibly chosen to exploit psychoacoustic phenomena (masking) Bandwidth Extrapolation of Audio Signals

  8. , Principal Components Analysis • Quasi-stationarity of windowed audio signals • PCA applied on the LOT coefficients • Classification of LOT blocks may be necessary Bandwidth Extrapolation of Audio Signals

  9. For simplicity of analysis, initiate study with single instrument audio signals Investigate the correlation among frequency components Implement linear estimator and PCA Compare results Perceptual quality Mean square error Experiment Bandwidth Extrapolation of Audio Signals

  10. Extrapolation should improve the quality However: Expected Results “Several approaches were considered to extrapolate the high frequency spectral envelope. In all cases, the subjective quality was not satisfactory. This suggests that the high frequency formant structure of speech cannot be accurately predicted from the narrowband formants.” - J. Valin & R. Lefebvre, Bandwidth Extension of Narrowband Speech for Low Bit-rate Wideband Coding, IEEE, 2000 • Extensions may be necessary Bandwidth Extrapolation of Audio Signals

  11. Week 1: Investigate the relationship between the low and high LOT coefficients Quantify the relations that can be exploited Week 2: Carry out the linear estimation based on the knowledge of the LOT coefficients Week 3: Extend to PCA Week 4: Compare the results Prepare writeup and presentation Workplan Bandwidth Extrapolation of Audio Signals

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