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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
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Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
Bandwidth Extrapolation of Audio Signals
Sung-Won YoonDavid Choi
February 8th, 2001
Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
Outline
• Motivation• Proposed system• Lapped orthogonal transform (LOT)• High frequency regeneration• Experiment• Expected results• Workplan
Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
Bandwidth Extrapolation
• Results should be– Similar to original wideband signal– Perceptually better quality
NarrowbandLOT coefficients
Wideband LOT coefficientsnonlinear system
X X Y
Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
Proposed System
LOT
LOT-1
High FrequencyRegeneration
2
Narrowband signal Wideband
signal
LPFLOT
Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
Lapped Orthogonal TransformH. Malvar & D. Staelin, 1989
tx2N
50% Overlap
2N N
LOT coefficient
• Avoids blocking artifact• No increase in bit rate
Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
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
XfY p
X Y
From narrowband signal
Regenerated high frequency
Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
Linear Estimation
• Each estimated high frequency coefficient is a weighted combination of the low freq. coefficients
ijii
j XwY
• Possible sparse representation of weights
• Weights possibly chosen to exploit psychoacoustic phenomena (masking)
Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
Principal Components Analysis
H
L
XY TLH
),...,(
....
1
1
N
N
diag
zzR ,
• Quasi-stationarity of windowed audio signals• PCA applied on the LOT coefficients
• Classification of LOT blocks may be necessary
Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
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 PCA4. Compare results
- Perceptual quality- Mean square error
Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
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
Bandwidth Extrapolation of Audio SignalsSung-Won Yoon, David Choi EE368C Project Proposal
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
