Low-Power MPEG-4 HE-AAC Version-2 Encodercmliu/Courses/... · Computational Complexity Filter Bank 32 (=2048/64) 64-pt DCTs-IV are saved for per frame. PS and SBR reduce about 50%

Low-Power MPEG-4

HE-AAC Version-2 Encoder

Chi-Min LiuHan-Wen Hsu

Chung-Han YangWen-Chieh Lee

http://psplab.csie.nctu.edu.tw

Outline

Introduction

Overview of CEMFB and CMFB

Parameter Extraction in CMFB

Down-Mixing by Phase Adjustment

Quality Measurement

Introduction

HE-AAC v.2 SBR+PS+AAC.

“Low-Power” Encoder A Fast Computation algorithm by simplifying the

computation from complex domain to real domainwith a limited quality degradation.

SBR

AACPS

Introduction

SBR — Bandwidth extension

Original Spectrum Decoded AAC LF Spectrum

HF Generation in SBR HF Adjustment in SBR

Introduction

PS coding — Stereo extension

Introduction

HE-AAC Encoder

SynthesisCEMFB

AACEncoder

SBREncoder

StereoParameterExtractor

HybridAnalysis

Filterbank

Down-Mixing

AACSBRPSBit-Stream Formatter

AnalysisCEMFB

L

RM

Introduction

Modules involved in “Low Power” Encoders Complex Exponential Filterbanks.

Data Calculation in Complex Domain

SynthesisCEMFB

AACEncoder

SBREncoder


HybridAnalysis

Filterbank

Down-Mixing


AnalysisCEMFB

L

RM

Introduction

Addressed Problem Our previous papers on Low Power SBR in AES 122

This paper on PS.

SynthesisCEMFB

AACEncoder

SBREncoder


HybridAnalysis

Filterbank

Down-Mixing


AnalysisCEMFB

L

RM

Outline

Introduction




Quality Measurement

CMFB (Cosine Modulated Filter Bank)

CEMFB (Complex-Exponential Modulated Filter Bank)

0Q1Q 2Q 3Q*

0Q*

1Q*

2Q*

3Q

04-channel CMFB

0Q1Q 2Q 3Q

04-channel CEMFB



Why is CEMFB adopted?CEMFB CMFB

X 2 X 2X 1 X 1

Aliasing Free Aliasing Suffering


Aliasing in CMFB

4-channel CMFB0

0Y0

0Y

0

1Y0

1Y

0

2Y0

2Y

0

3Y0

3Y

Freq.-π/2M π/2M -π π0

)(zHk

][nx

1

0Y3

0Y1

0Y 2

0Y2

0Y 3

0Y

2

1Y1

1Y3

1Y 1

1Y3

1Y 2

1Y

2

2Y3

2Y1

2Y 2

2Y 3

2Y1

2Y

3

3Y1

3Y2

3Y2

3Y 3

3Y1

3Y


M M )(zFk

][ˆ nxk

0

1Y0

1Y

0

0Y0

0Y

0

2Y0

2Y

0

3Y0

3Y

Aliasing Eliminationby a Mutually

“Perfect” Cancellation


Aliasing in CEMFB

0

3Y


0

0Y

0

1Y

0

2Y

)(zHk

][nx

4-channel CEMFB

M M

2

3Y 3

3Y 0

3Y1

3Y


1

0Y3

0Y0

0Y2

0Y

3

1Y 0

1Y 1

1Y2

1Y

0

2Y2

2Y3

2Y1

2Y

)(zFk

][ˆ nxk

0

3Y

0

0Y

0

1Y

0

2Y

Aliasing Elimination by near -zero overlap

Outline

Introduction


Parameter Extraction in CMFB Signal Modeling

IID (Inter-channel Intensity Difference)

ICC (Inter-Channel Coherence)


Quality Measurement

-20 -15 -10 -5 0 5 10 15 20-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

Parameter Extraction in CEMFB —

Analytic Modeling for CEMFB Subband Signals

Hilbert transform

0 0

0 )2/(sin2

][

2

n

nn

nnh

, ][][][ˆ

k

knxkhnx

j

j)( jeH

90-degree phase shifter

-π π

ω

2


Analytic Modeling for CEMFB Subband Signals

CMFB subband

CEMFB subband

][ˆ][][ nxjnxnx

-π π

ω

1

1

1

)( jejH

Image part is cancelled.

Analytic signal

otherwise

eXeX

j

j

,0

0,2

real

image][nx


Cross-Correlation Function

Cross-correlation

Signal energy

ICC (Inter-Channel Coherence)

)()()(][][)( *

,

*

,

jjj

yx

k

yx eYeXeRnkykxnr

deYeXr jj

yx )()()0( *

21

,

deXeXr jj

xx )()(2

1)0( *

,

Energy of real signal (CMFB)

Energy of analytic signal (CEMFB)

Energy relation


Energy Relation of Real and Analytic Signals

0

*

24

, )()()0( deXeXrE jj

xxx

xx EE 2

0

**

, )()(2

2)()(

2

1)0( deXeXdeXeXrE jjjj

xxx


Cross-Correlation Relation of Real and Analytic Signals

ICC for real signals (CMFB)

0

22

21

*

21

,,

)()()(

)()()0(

deRdeIjeR

deYeXr

jjj

jj

yxyx

-π π

ω

1

)()(* jj eYeX

The image term of X*Y are cancelled mutually.



ICC for analytic signals (CEMFB)

00

24

0

*

24

,,

)()(

)()()0(

deIjdeR

deYeXr

jj

jj

yxyx

-π π

ω

4

)()(4 * jj eYeX

The image term of X*Y are kept.



ICC for real and analytic signals

ICC relations

)0()()()0( ,21

0

*

22

,, yx

jj

yxyx rdeYeXr

0

24

,, )(2 deIj j

yxyx

yxyx ,, 2


Extraction ofIID and ICC Parameters

)()(2

)(2log10

)(

)(log10)( ,1010,

biidbe

be

be

bebiid rl

r

l

r

l

rl

h

l

k

kk

L

n

Ll nnklbe

1

0

2

21,)(

h

l

k

kk

L

n

Lr nnkrbe

1

0

2

21,)(

xx EE 2

IID (Inter-channel Intensity Difference) approximation

)()( ,,biidbiid rlrl


Extraction ofIID and ICC Parameters

ICC approximation

,1,1,)(1

0

2

*

2,

h

l

k

kk

L

n

LLrl nnkrnnklbe

)()(

)(

)(2)(2

)(2

)()(

)()(

,,,

, bebe

be

bebe

be

bebe

bebicc

rl

rl

rl

rl

rl

rl

rl

xx EE 2 yxyx ,, 2

)()(

)()(

,

, bebe

bebicc

rl

rl

rl

Down-Mixing by Phase AdjustmentCEMFB —

Summary

Relations between the real and analytic signals

Approximation of IID and ICC

xx EE 2

yxyx ,, 2

)()(

)()(

,

, bebe

bebicc

rl

rl

rl

)()( ,,biidbiid rlrl

Only one channel needs CEMFB.

Outline

Introduction




Quality Measurement


Adjustment Phase Extraction

CEMFB Subband

CMFB Subband

Down-mixing Subband

ie21

][][][21 nyenxnd i

1

0

2

21

)2,0[][][maxarg

N

n

i nyenx

1

0

* ][][N

n

nynx

1

0

*

1

0

*

][][

][][

N

n

N

nj

nynx

nynx

e

KLT-like Criterion

Down-Mixing by Phase Adjustment—

Comparison for sc03.wav

with Phase Adjustment

without Phase Adjustment

ODG: -2.86

ODG: -3.06


Tone Modulation Artifact


Smooth Method

Cosine smooth connection of coefficient vector

FrameiFramei+1

k0

i

1i

time index

n

FrameiFramei+1

k0

i

1i

time index

n 2

cos2

11

iiii

k

nn


Artifact Reduction by Smooth Method

Outline

Introduction


Parameter Extraction in CEMFB


Quality Measurement

Complex HE-AAC V.2

Complex HE-AAC V.2 + KLT Down-Mix

LP HE-AAC V.2 Real HE-AAC V.2 LP HE-AAC V.2 + KLT-like Down-Mix

es01 -2.21 -2.18 -2.25 -2.24 -2.29

es02 -2.71 -2.73 -2.7 -2.7 -2.8

es03 -2.82 -2.84 -2.79 -2.79 -2.85

sc01 -3.3 -3.18 -3.32 -3.33 -3.24

sc02 -3 -3.05 -3 -3.02 -3.09

sc03 -2.62 -2.65 -2.56 -2.74 -2.57

si01 -2.75 -3.02 -2.72 -2.77 -2.95

si02 -2.63 -2.42 -2.68 -2.74 -2.46

si03 -1.99 -2.19 -2.03 -2.02 -2.31

sm01 -2.89 -3.05 -2.86 -2.96 -3.06

sm02 -3.15 -3.05 -3.13 -3.23 -3.13

sm03 -2.52 -2.55 -2.52 -2.56 -2.51

AVG -2.7158 -2.7425 -2.7133 -2.7583 -2.7717

ODG Comparison @ 36kbps

Real HE-AAC v.2 ODG: -3.23

LP HE-AAC v.2ODG: -3.13

AVG ODG Comparison @ 24k, 36k and 48k bps

AVG ODG

-3.5

-3.3

-3.1

-2.9

-2.7

-2.5

-2.3

-2.1

48k 36k 24k

OD

G

Complex Low Power Real

Remarks

Low Power Merits Computation, Data Movement, Memory.

SynthesisCEMFB

AACEncoder

SBREncoder


HybridAnalysis

Filterbank

Down-Mixing


AnalysisCEMFB

L

RM

Computational Complexity

Filter Bank 32 (=2048/64) 64-pt DCTs-IV are saved for per

frame.

PS and SBR reduce about 50% cost for IID, ICC, energy, and tonality computation.

Complex LP LP + KLT-Like Adustment

128-64 Analysis FB

2*264-pt DCT-IV

2+1 64-pt DCT-IV

2+1 64-pt DCT-IV

64-32 Downsampled Synthesis FB

1 64-pt DCT-IV

1 32-pt DCT-IV

1 64-pt DCT-IV

Q & Ahttp://psplab.csie.nctu.edu.tw

Computational Complexity

Filter Bank

Complex: 5 64-pt DCTs.

LP: 3 64-pt DCTs, 1 32-pt DCTs.

LP + KLT-like: 4 64-pt DCTs.

PS and SBR reduces about 50% cost for IID, ICC, energy, and tonality computation.


CEMFB Subband

CMFB Subband

Down-mixing Subband

ie21

For AAC


CEMFB Subband

CMFB Subband

Down-mixing Subband

ie21

21

Real Part

For SBR

備註

48k 36k 24k

Com LP All Real com LP All Real com LP All Real

es01 -1.36 -1.47 -1.45 -2.21 -2.25 -2.24 -3.17 -3.26 -3.3

es02 -1.43 -1.45 -1.45 -2.71 -2.7 -2.7 -3.47 -3.46 -3.49

es03 -1.61 -1.61 -1.61 -2.82 -2.79 -2.79 -3.69 -3.68 -3.69

sc01 -3.24 -3.26 -3.28 -3.3 -3.32 -3.33 -3.39 -3.41 -3.44

sc02 -2.88 -2.87 -2.91 -3 -3 -3.02 -3.24 -3.21 -3.23

sc03 -2.29 -2.25 -2.52 -2.62 -2.56 -2.74 -2.96 -2.96 -2.99

si01 -2.59 -2.55 -2.59 -2.75 -2.72 -2.77 -3 -2.99 -3.08

si02 -2.37 -2.41 -2.52 -2.63 -2.68 -2.74 -3.31 -3.29 -3.27

si03 -1.63 -1.74 -1.72 -1.99 -2.03 -2.02 -2.85 -3 -3.03

sm01 -2.66 -2.64 -2.76 -2.89 -2.86 -2.96 -3.42 -3.46 -3.52

sm02 -2.91 -2.81 -2.9 -3.15 -3.13 -3.23 -3.52 -3.49 -3.52

sm03 -2.4 -2.4 -2.46 -2.52 -2.52 -2.56 -2.84 -2.88 -2.91

average -2.2808 -2.2883 -2.3475 -2.7158 -2.7133 -2.7583 -3.2383 -3.2575 -3.2892

Documents

Low-Power MPEG-4 HE-AAC Version-2 Encodercmliu/Courses/... · Computational Complexity Filter Bank 32 (=2048/64) 64-pt DCTs-IV are saved for per frame. PS and SBR reduce about 50%