Effect of the Phase on Effect of the Phase on Speech and Musical Speech and Musical signals using DWT signals using DWT

By:By:Hafiz, MalikHafiz, Malik

ECE418,DSPIIECE418,DSPIISpring,02Spring,02

Talk outlineTalk outline

IntroductionIntroduction Block DiagramBlock Diagram ResultsResults ApplicationsApplications conclusionconclusion

IntroductionIntroduction

What is Phase and phase-shift?What is Phase and phase-shift? Effect of the phase on the signals?Effect of the phase on the signals? How to play with phase?How to play with phase?

What is phase & phase shift?What is phase & phase shift?

Start/peak location of a signal with certain Start/peak location of a signal with certain reference. reference.

Phase shift is nothing more than a temporal shift.Phase shift is nothing more than a temporal shift.

The red curve is the original signal, the blue one is the signal that has been phase-shifted; in black, the result of adding these two.

Effect of the phase-shift on the Effect of the phase-shift on the mixed signalsmixed signals

XXresultresult = = XXorignalorignal+ + XXshiftshift

when summing two identical signals, one phase-shifted a when summing two identical signals, one phase-shifted a few milliseconds vs. the other, some frequencies will be few milliseconds vs. the other, some frequencies will be amplified, some others will be attenuated.amplified, some others will be attenuated.

The higher in the frequency spectrum, the more noticeable The higher in the frequency spectrum, the more noticeable

the changes in the resulting sound.the changes in the resulting sound.

All-Pass Systems and their All-Pass Systems and their applicationsapplications

What are All-Pass Filters ?What are All-Pass Filters ? Can I use All-Pass Filters to shift the Can I use All-Pass Filters to shift the

Phase….???Phase….??? Yes! Why not…Yes! Why not…

Overview of All-pass systems Overview of All-pass systems

• Pole-Zero

• Magnitude • Phase

How to play with phase???How to play with phase???

1.1. Using Transformed domain i.e. Using Transformed domain i.e. FT,CT, etcFT,CT, etc

2.2. Using all-Pass filtersUsing all-Pass filters

Block DiagramBlock Diagram

Output Audio

waveletAnalysis

Filterbank

All-Pass system

waveletsynthesis

Filterbank

Input Audio

Wavelet Analysis/SynthesisWavelet Analysis/Synthesis Filter Banks with phase shift system Filter Banks with phase shift system

output audio with embedded

data

HPF

LPF

APF

LPF

LPFLPF

APF

HPFAPF

Data hiding

Input audio

Result: Result: Using All-Pass filters & DWTUsing All-Pass filters & DWT

cDs & cA Superimposed coef.

Result2: Result2: Using All-Pass filters & DWTUsing All-Pass filters & DWT

A8 & D8 onlyD1 only

Results….Results….

D8 & A8 D1 only With all

original

Musical signal

Results… Results…

original

With allD1 onlyA8 & D8

Audio signal

Magnitude Response due to phase-Magnitude Response due to phase-shiftshift

original D8 only

A8 & D8With all

ApplicationsApplications

Data HidingData Hiding1.1. WatermarkingWatermarking

2.2. CaptioningCaptioning

Hiding signature to the songsHiding signature to the songs Hiding signature to the imagesHiding signature to the images

Future DirectionFuture Direction

More sophisticated system for data hiding can be More sophisticated system for data hiding can be developed with out deteriorating the quality of developed with out deteriorating the quality of the audio by exploiting the fact that human the audio by exploiting the fact that human perception is bit insensitive to certain bands of perception is bit insensitive to certain bands of frequency. frequency.

This thing can be done by frequency selective This thing can be done by frequency selective phase-shifting.phase-shifting.

This method i.e. frequency selective phase-This method i.e. frequency selective phase-shifting will also work for images as well as video.shifting will also work for images as well as video.

Thanks!!!!Thanks!!!!

Hafiz, MalikHafiz, Malik