LIST OF FIGURES. Figure No. Title Page No. Fig. l. l Fig. l.2

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1 LIST OF FIGURES Figure No. Title Page No. Fig. l. l Fig. l.2 Fig. l.3 A generic perceptual audio coder. 3 Schematic diagram of the programme of the present work on perceptual audio coding. 18 Schematic diagram of the programme of the present work on enhancement and modification of speech and audio for the hearing impaired. 19 Basic structure of the ISONPEG audio encoder. 22 ISONPEG Audio decoder. 22 Human auditory system. 27 Cochlea. 28 Cross section of basilar membrane. 28 Resonant frequencies of various points along the basilar membrane. 29 Hearing threshold in quiet. 30 The frequency-to-place transformation. 3 1 Noise masking tone. 35 Tone masking noise. 35 Schematic representation of simultaneous masking. 36 Time and frequency resolution. 45 Subband coding scheme. 47 Flow diagram of time-scale analysis algorithm. 48 Logarithmic set of bandwidths. 49 Orthogonal subband coding scheme. Biorthogonal subband coding scheme. Wavelet packet decomposition. Haar-scaling and wavelet functions. Daubechies- scaling and wavelet functions. Symlet- scaling and wavelet functions. Coiflet- scaling and wavelet functions. Biorthogonal spline- scaling and wavelet functions. Block diagram of the proposed audio coder.

2 DWT tree structure of the proposed audio coder. DWT based audio decoder. Local maxima. Tonal maskers. Tonal and non-tonal maskers. Non-tonal components vs. absolute threshold. Tonal component vs. absolute threshold. Elimination of tonal components too closed to each other. Masking thresholds. Global masking threshold. Flow chart for making the raw codebook. Flow chart for optimizing the codebook. Encoder and decoder algorithms. Variation of compression ratio with order of the wavelet (Daubechies family). Variation of coding delay with order of the wavelet (Daubechies family). Variation of compression ratio with order of the wavelet (Symlet family). Variation of coding delay with order of the wavelet. (Symlet family). Performance of various wavelets on different frames of audio signal ('kadalinakkare.wav'). Performance of various wavelets on different frames of audio signal ('castanets.wav'). Enhanced DWT based audio coder. Pre-echo distortion in MPEG standard. Pre-echo distortion elimination in the proposed audio coder. Error power spectra plot (one frame of 'castanets'). Power spectra plot-castanets: DCT and Scalar quantization. Power spectra plot- castanets: DWT and Scalar quantization. Power spectra plot-castanets: DWT and Vector quantization. Power spectra plot-castanets: DWT and Scalar + VQ. Block diagram of the wavelet packet based audio coder. Wavelet packet decomposition. xvi

3 Block diagram of the enhanced wavelet packet based audio encoder. 132 Power spectra plot - castanets: DWP and scalar quantization. 138 Power spectra plot - castanets: DWP and vector quantization. 138 Power spectra plot - castanets: DWP and scalar + VQ. 139 Power spectra plot - else3: DWP and scalar quantization. 139 Power spectra plot - else3: DWP and vector quantization. 140 Power spectra plot - else3: DWP and scalar + VQ. 140 Block diagram of the proposed low complexity wavelet packet based audio coder. 140 Global masking threshold for frame 10 of castanets.wav. 141 Quantization noise level. 142 Power spectra plot - castanets: Low complexity scheme with scalar quantization. 142 Power spectra plot - castanets: Low complexity scheme with vector quantization. 148 Power spectra plot - castanets: Low complexity scheme with scalar + VQ. 149 Power spectra plot - else3: Low complexity scheme with scalar quantization. 149 Power spectra plot - else3: Low complexity scheme with vector quantization. Power spectra plot - else3: Low complexity scheme with scalar + VQ. Block diagram of scalable perceptual audio coding scheme. 151 Flexible wavelet packet tree structure designed to support three sampling kquencies.. Power spectra plot - clap: Flexible DWP and scalar quantization. 157 Power spectra plot - clap: Flexible DWP and vector quantization. 157 Power spectra plot - male: Flexible DWP and scalar quantization. 158 Power spectra plot - male: Flexible DWP and vector quantization. 158 Power spectra plot - crow: Flexible DWP and scalar quantization. 159 Power spectra plot - crow: Flexible DWP and vector quantization. 159 Power spectra plot - crow: Flexible DWP and scalar + VQ. 160 Power spectra plot - female2: Flexible DWP and scalar quantization. 160 xvii

4 Fig.5.33 Fig.5.34 Fig.5.35 Fig.5.36 Fig.6.1 (a) Fig.6.1 (b) Fig.6.1 (c) Fig.6.1 (d) Fig.6.1 (e) Fig.6.2 Fig.6.3 Fig.6.4 Fig.6.5 Fig.6.6 (a) Fig.6.6 (b) Fig.6.6 (c) Fig.6.6 (d) Fig.6.6 (e) Fig.6.7 Fig.6.8 Fig.6.9 Fig.6.10 Fig.6. l l (a) Fig.6. l l (b) Fig.6.11 (c) Fig.6.11 (d) Fig.6.11 (e) Power spectra plot - female2: Flexible DWP and vector quantization. Power spectra plot - female2: Flexible DWP and scalar + VQ. Power spectra plot - castanets: Flexible DWP and scalar quantization. Power spectra plot - castanets: Flexible DWP and vector quantization. Power spectra plot - castanets: Flexible DWP and scalar + VQ. Power spectra plot - else3: Flexible DWP and scalar quantization. Power spectra plot - else3: Flexible DWP and vector quantization. Power spectra plot - else3: Flexible DWP and scalar + VQ. Plot of original signal ('clap'). Plot of reconstructed signal (CR=6). Plot of reconstructed signal (CR=10). Plot of reconstructed signal (CR= 15). Plot of reconstructed signal (CR=25). Power spectra plot (clap, CR=6). Power spectra plot (clap, CR=lO). Power spectra plot (clap, CR=15). Power spectra plot (clap, CR=25). Plot of original signal ('female2'). Plot of reconstructed signal (CR=6). Plot of reconstructed signal (CR= 10). Plot of reconstructed signal (CR= 15). Plot of reconstructed signal (CR=25). Power spectra plot (female2, CR=6). Power spectra plot (female2, CR=lO). Power spectra plot (female2, CR=15). Power spectra plot (female2, CR=25). Plot of original signal ('castanets'). Plot of reconstructed signal (CR=6). Plot of reconstructed signal (CR=10). Plot of reconstructed signal (CR= 15). Plot of reconstructed signal (CR=25).

5 Power spectra plot (castanets, CR=6). Power spectra plot (castanets, CR=lO). Power spectra plot (castanets, CR=15). Power spectra plot (castanets, CR=25). Block diagram of two stage SNR scalable audio codec. Performance of two stage SNR scalable audio codec ('castanets', 'CR=25'); Power spectra plots at 1 and 2 for two stage SNR scalable audio codec. ('castanets','cr=25'). Performance of two stage SNR scalable audio codec ('clap', 'CR=25'). Power spectra plots at 1 and 2 for two stage SNR scalable audio codec. ('clap','cr=25'). Performance of two stage SNR scalable audio codec ('clap', 'CR=lO'). Power spectra plots at 1 and 2 for two stage SNR scalable audio codec. ('clap', 'CR=lO'). Sample audiogram of a normal person Sample audiogram of an impaired person with sensorineural deafness Basic hearing model. Block diagram of the generic elecronic hearing aid. Block diagram of the generic digital hearing aid. DWT tree structure according to the audiogram standard with octave steps. Soft thresholding characteristics. Hearing aid output for patient 2 (signal-clap without noise). (signal-clap without noise). Hearing aid output for patient 2 (signal-clap with noise). (signal-clap with noise). Hearing aid output for patient 2 (signal-female voice without noise). 220 (signal-female voice without noise). 220 Hearing aid output for patient 2 (signal-female voice with noise). 221

6 (signal-female voice with noise) Hearing aid output for patient 12 (signal-clap without noise). 222 Wavelet coefficients before and after modification for patient12 (signal-clap without noise). 222 Hearing aid output for patient 12 (signal-female voice without noise). Wavelet coefficients before and after modification for patient 12 (signal-female voice without noise). 223 Hearing aid output for patient 12 (signal-clap with noise). 224 (signal- clap with noise). 224 Hearing aid output for patient 12 (signal-female voice with noise). 225 Wavelet coefficients before and after modification for patient l2 (signal-female voice with noise). 225 Audiogram standard (half octave steps). 226 Wavelet packet tree structure for digital hearing aid Original signal and hearing aid outputs (signal- clap without noise). 228