Block Diagram of MPEG AAC

55 Pages·2009·5.76 MB·English

Design of MPEG-4 AAC Encoder
Authors:
Chi-Min Liu, Wen-Chieh Lee, Chung-Han Yang, Kang-
Yan Peng, Ting Chiou, Tzu-Wen Chang, Yu-Hua Hsiao,
Hen-Wen Hue and Chu-Ting Chien
Outline
Introduction

Psychoacoustic Model

M/S Coding

Window Switch

Temporal Noise Shaping

Experiments & Demonstration

Conclusion

Introduction–
NCTU-AAC Encoder
Audio in
W-Switch
Psychoacoustic
Model
Filterbank
g
n
i
k
TNS c
Bit Reservoir
a
P

m
a
M/S e
r
t
S
-
t
i
B
Bit Allocation Quantization
VLC
Introduction–
NCTU-AAC Encoder
Audio in
W-Switch
Psychoacoustic
Model
Filterbank
g
n
i
k
TNS c
Bit Reservoir
a
P

m
a
M/S e
r
t
S
-
t
i
B
Bit Allocation Quantization
VLC
1. Introduction–
NCTU-AAC Encoder
Audio in
W-Switch
Psychoacoustic
Model
Filterbank
g
n
i
k
TNS c
Bit Reservoir
a
P

m
a
M/S e
r
t
S
-
t
i
B
Bit Allocation Quantization
VLC
1. Introduction
Modules

Psychoacoustic Model

M/S Coding

Window Switch

Temporal Noise Shaping

Objective

Theoretical Frameworks

Quality

Complexity

2. Psychoacoustic Model
Approach

MDCT-based instead of FFT-based.

New Masking Models

Detection of tonal attack band.

Detection of tone-rich signal.

2. Psychoacoustic Model (c.1)
MDCT and FFT

Similar spectrum.

MDCT spectrum is

chaotic due to the
aliasing.
MDCT leads to the

consistent spectrum
for analysis and
encoding process.
2. Psychoacoustic Model (c.2)
DCT Spectrum
Q-Bands instead of Lines or P-Bands

Tone/Noise information based on

Band Flatness instead of Frame Predictivity

GM N1 1 1 N1
flatness  b , GM  x , AM  x
N
b b i b i
AM N
b i0 i0
For tone-rich signal in band, flatness approximates to 0

b
For noise-rich signal in band, flatness approximates to 1

b
2. Psychoacoustic Model--
Adaptive TMN and NMT offset
Utilization Human Perception

Insensitivity in high frequency

The masking effect in high frequency is

higher than the lower one
Offset
4
3.5
3
2.5
2 Offset
1.5
1
0.5
0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49