Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals Sung-Won Yoon David Choi February 8 th, 2001

Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals Outline Motivation Proposed system Lapped orthogonal transform (LOT) High frequency regeneration Experiment Expected results Workplan

Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals Bandwidth Extrapolation Results should be –Similar to original wideband signal –Perceptually better quality Narrowband LOT coefficients Wideband LOT coefficients nonlinear system XXY

Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals Proposed System LOT LOT -1 High Frequency Regeneration 2 Narrowband signal Wideband signal LPF LOT

Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals Lapped Orthogonal Transform H. Malvar & D. Staelin, N 50% Overlap 2NN LOT coefficient Avoids blocking artifact No increase in bit rate

Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals High Frequency Regeneration Trained system Parameters p are chosen to fit the training data Mapping from narrowband signal to wideband signal –Estimate LOT coefficients –Magnitude only XY From narrowband signal Regenerated high frequency

Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals Linear Estimation Each estimated high frequency coefficient is a weighted combination of the low freq. coefficients Possible sparse representation of weights Weights possibly chosen to exploit psychoacoustic phenomena (masking)

Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals Principal Components Analysis, Quasi-stationarity of windowed audio signals PCA applied on the LOT coefficients Classification of LOT blocks may be necessary

Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals Experiment 1.For simplicity of analysis, initiate study with single instrument audio signals 2.Investigate the correlation among frequency components 3.Implement linear estimator and PCA 4.Compare results -Perceptual quality -Mean square error

Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals Expected Results Extrapolation should improve the quality However: Extensions may be necessary “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

Sung-Won Yoon, David ChoiEE368C Project Proposal Bandwidth Extrapolation of Audio Signals Workplan 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