class auditory perception

7/28/2019 Class Auditory Perception

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Department of Electrical & Computer Engineering

Auditory Perception

Meena Ramani

04/09/2004


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Note

For this lecture many of the slides will be

accompanied by scanned pictures shown onthe OHP from Zwicker and Fastls

Psycho-acoustics facts and models 2nd edition


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Main Outline

Anatomy of the Ear and Hearing DONE

Auditory perception

Hearing aids and Cochlear implants.

Extra: Direction of Arrival Estimation


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Auditory perception

Shepard Tones

Masking

Ohms Acoustic Law Critical Bands

Webers law

Just Noticeable Frequency


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Roger Penrose M.C. Escher

Ascending andDescending

OpticalIllusion

AudioIllusion


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Shepard Tones Circularity in Judgments of Relative Pitch, Roger N. Shepard,

JASA 1964.

Sensitivity to descending pitch

Sensitivity to volume changes between thesepitches.

A set of eight tones all an octave apart

The tones simultaneously descend in pitch till half oftheir original pitch.

Jump back up to their original pitch and repeat the cycle.

Perceive this change?

Unique volume curve

Effect: Seamless transition in the cycle.

Its all in your head!

Omit two of the eight tones in the mid frequency range.
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You know I can't hear you when the water isrunning!

MASKING
http://images.google.com/imgres?imgurl=http://www.clallam.net/EnvHealth/assets/images/tap_water.jpg&imgrefurl=http://www.clallam.net/EnvHealth/html/dw_availability.htm&h=192&w=169&sz=6&tbnid=Cs8vMAYzLjwJ:&tbnh=97&tbnw=86&start=20&prev=/images%3Fq%3Dtap%2Bwater%26hl%3Den%26lr%3D%26rls%3DGGLD,GGLD:2004-10,GGLD:en%26sa%3DNhttp://images.google.com/imgres?imgurl=http://www.cbfisap.sfa.ed.gov/tutorial/lesson5/images/phone.gif&imgrefurl=http://www.cbfisap.sfa.ed.gov/tutorial/lesson5/l05_008.htm&h=250&w=198&sz=13&tbnid=VOO6YPrv3IsJ:&tbnh=104&tbnw=83&start=66&prev=/images%3Fq%3Dcell%2Bphone%2Bman%26start%3D60%26hl%3Den%26lr%3D%26rls%3DGGLD,GGLD:2004-10,GGLD:en%26sa%3DNhttp://images.google.com/imgres?imgurl=http://homepage.ntlworld.com/myronf/images/mask.jpg&imgrefurl=http://homepage.ntlworld.com/myronf/mask.html&h=599&w=899&sz=44&tbnid=D-YQopVtFMkJ:&tbnh=96&tbnw=144&start=42&prev=/images%3Fq%3Dmask%2B%26start%3D40%26hl%3Den%26lr%3D%26rls%3DGGLD,GGLD:2004-10,GGLD:en%26sa%3DN


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Masking

Low-frequency, broad banded sounds (like water running) will maskhigher frequency sounds which are softer at the listener's ear (a

conversational tone from across the room).

Example 2: Truck in street

Masking occurs because two frequencies lie within a critical band and

the higher amplitude one masks the lower amplitude signal. Masking can be because ofbroad band, narrowband noise, pure and

complex tones.

Masking threshold

Amount of dB for test tone to be just audible in presence of noise

See OHP Figure
http://images.google.com/imgres?imgurl=http://homepage.ntlworld.com/myronf/images/mask.jpg&imgrefurl=http://homepage.ntlworld.com/myronf/mask.html&h=599&w=899&sz=44&tbnid=D-YQopVtFMkJ:&tbnh=96&tbnw=144&start=42&prev=/images%3Fq%3Dmask%2B%26start%3D40%26hl%3Den%26lr%3D%26rls%3DGGLD,GGLD:2004-10,GGLD:en%26sa%3DN


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Masking by Broad band noise

White noise- frequency independent PSD

Masked thresholds are a function of frequency.

Low and very high frequency almost same as TOQ.

Above 500Hz, thresholds increase with increase in frequency

Increasing white noise by 10dB increases masked threshold up by10dB for frequencies >500Hz.

=>Linear behavior of masking

NOTE: TOQs frequency dependence almost completelydisappearsEars frequency selectivity and critical bands.

See OHP Figure


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Masking by Narrow band noise

Narrow band


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Masking by Narrow band noise (cont)

Noise (Varying Amplitude, Fixed Frequency)

1KHz noise

20-100dB

Slope of rise seems independent of Amplitude

But slope of fall is dependent on amplitude Non-Linear frequency dependence

Strange effect at high masker amplitudes:

At high amplitudes ear begins to listen to anything audible!!

Begin to hear difference noise (noise and testing tone)

See OHP Figure


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Masking by Pure and Complex tones Pure tones:

Below threshold of Quiet of test tone can hear only masking tone

Above it


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Temporal Aspects of Masking

Previously assume long lasting test and masking sounds

Speech has a strong temporal structure

Vowels --loudest parts

Consonants faint

Often plosive consonants are masked by preceding loud vowel


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Temporal Aspects of Masking (cont)

Simultaneous Masking

Pre-Stimulus/Backward/Premasking

1st

test tone 2nd

Masker Poststimulus/Forward/Postmasking

1st Masker 2nd test tone


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Types of MaskingSimultaneous masking

Duration less than 200ms test tone threshold increases with decrease induration.

Duration >200ms constant test tone threshold

Assume hearing system integrates over a period of 200ms

Postmasking (100ms)

Decay in effect of masker 100ms More dominant

Premasking (20ms) Takes place before masker is on!!

Each sensation is not instantaneous , requires build-up time

Quick build up for loud maskers Slower build up for softer maskers

Less dominant effect

See OHP Figure


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Ohms Acoustic Law

The sound quality of a complex tone depends ONLY on theamplitudes and NOT relative phases of its harmonics.


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Critical Bands

Proposed by Fletcher Noise which masks a test tone is the part of its spectrum which lies

near the tone

Masking is achieved when the power of the tone and the power

of the noise spectrum lying near the tone and masking it are

the same.

Bands defined this way have a BW which produces same acoustic

power in the tone and in the noise in the band when the tone is

masked.CRITICAL BANDS

See OHP Figure


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Critical Band (cont.)

How to measure?

Masking of a band pass noise using 2 tones

CB corresponds with1.5mm spacing on BM.

24 such band pass filters

BW of the filters increases with increasing center frequency Logarithmic relationshipWebers law example.

Bark scale

See OHP Figure


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Webers law

Weber's Law states that the ratio of the increment threshold tothe background intensity is a constant.

So when you are in a noisy environment you must shout to be heard

while a whisper works in a quiet room.

when you measure increment thresholds on various intensitybackgrounds, the thresholds increase in proportion to the

background.


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Just noticeable change in

Frequency (Pg:183)

Similar to variation in the critical band structure

This is because it depends on number of BPFs

More BPF better resolution

Till about 500Hz JND is about 3.6Hz. After 500Hz it varies as 0.007f

See OHP Figure
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HEARINGAIDS
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Outline

Facts on hearing loss

Cell phones and hearing loss

Types of Hearing aid Inside a hearing aid

Audiogram


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Facts on Hearing Lossin Adults

One in every ten (28 million) Americans has hearing loss.

The vast majority of Americans (95% or26 million) with hearing losscan have their hearing loss treated with hearing aids.

Only 5% of hearing loss in adults can be improved through medical orsurgical treatment

Millions of Americans with hearing loss could benefit fromhearing aids but avoid them because of the stigma.


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Cell phonesand Hearing aids

Cell Phones emit a type of electromagnetic energy that interfereswith the operation of hearing aids.

The Federal Communications Commission in mid-July 2003 orderedthe cell phone industry to help out the hard-of-hearing.

Within two years, cell-phone manufacturers must offer at leasttwo phones with reduced interference for each type of cellulartechnology used, or ensure that one-fourth of phones thecarriers sell produce less interference.

The FCCs final milestone is February 2008.


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Types ofHearing aids

Behind The earIn the Ear

In the Canal Completely in the

canal


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Anatomy of a HearingAid

Microphone

Tone hook

Volume control

On/off switch Battery compartment


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Inside aHearing aid

1: The microphone

The microphone picks up sound waves from the air and transformsthem into electrical signals.

2: The microphone suspension

The microphone suspension holds the microphone in place.

3: The loudspeaker

The loudspeaker sends the amplified sounds into your ear. The

loudspeaker is also called the receiver and sometimes the telephone.

4: The battery drawer

The battery drawer holds the battery in place.

5: The amplifier

The amplifier makes the signals that come from the microphone louder.

6: The telecoil

The telecoil makes it possible for you to hear one specific person if you

are in a place that supports the use of a telecoil. Many classrooms,

churches and cinemas have telecoil. The telecoil makes it possible for

you to hear i.e. your teacher without hearing the noise around you. It is

also possible to use the telecoil at home - with the TV or the radio.


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Audiograms


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Direction of Arrival (DOA) estimation algorithm


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Talk outline

Necessity for DOA

DOA algorithm Requirements Types of DOA algorithms

Delay and sum

Minimum variance

MUSIC

Coherent MUSIC

Root MUSIC ESPRIT

Comparison Measures

Computational Intensity comparison

Accuracy Comparison

Accuracy vs Computational intensity Conclusion


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Where does the DOA come into the picture?

Has 2 microphones

DOA Estimation

qs

& qn

Beamformer

Lets meet

at 11?!?

7 is good

for me

too!!

11 sounds

good!!
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Direction of Arrival Estimation Algorithms

The DOA algorithm must satisfy the following conditions :

Low computational intensity(MIPS/MFLOPS)

High accuracy(RMSE)

High speed Easy implementation

Good performance at low SNRs

Works on a 2 microphone array system with 4cm

separation between them.


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DOA Algorithms

Spatial Correlation

methods

Subspace decomposition

methods

MUSIC

Multiple Signal Estimation

ESPRIT

Estimation of Signal parameters

using rotational invariance

Delay and Sum Minimum Variance

Coherent MUSIC

Root MUSIC


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DOA Method Equation for Implementation

Delay and Sum

Minimum

Variance

MUSIC

Coherent

MUSIC

Root MUSIC

ESPRIT

*

( ) ( ) ( )P a Saq q q

*

1( )

( ) ( ) ( )P

a inv s aq

q q

*

* *

( ) ( )( )

( ) ( )N N

a aP

a E E a

q qq

q q

'( )

' 'N N

a aP

a E E aq

1 0sin . ( ) /( )K c angle z d q

10

sin arg( ) /( )K K

c dq


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Comparison Measures

To evaluate the computational intensity

MFLOPS comparison plot

To evaluate the accuracy

Root Mean Square Error comparison plot To evaluate the effect at low SNRs

SNR vs Estimated angle plot

To evaluate overall performance

Accuracy vs computational intensity


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Evaluation of computational Intensity:

MFLOPS comparison chart Min Variance

0.93 Mflops

Coherent MUSIC

0.3958 Mflops

DS

0.3573 Mflops

MUSIC

0.0813 Mflops

ESPRIT

0.0086 Mflops

Root MUSIC

0.0068 Mflops


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Comparison of accuracy at different SNR values

0 5 10 15 20 250

20

40

60

80

100

120

140

160

180

Frame Number

EstimatedDOA

(degrees)

Comparison of Estimated DOAs: SNR=10dB,Speech= 90' ,Noise=0'

ESPRITRMUSIC

CMUSICMUSICMVDS

0 5 10 150

20

40

60

80

100

120

140

160

180Estimated DOAS for only those regions which are speech

Frames Number

Estim

atedDOA(Degrees)


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Comparison of Accuracy-MFLOPS


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Conclusion

Tradeoff between Accuracy and Computational intensity

leads to the conclusion that ESPRIT is the Direction of

arrival estimation algorithm best suited for our purpose

MFLOPS value: 0.0086

RMSE value:~3 (at 10dB)

C i f E i d DOA SNR dB S h N i


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0 5 10 15 20 250

20

40

60

80

100

120

140

160

180

Frame Number

Estimate

dDOA

(degrees)

Comparison of Estimated DOAs: SNR=10dB,Speech= 90' ,Noise=0'

ESPRITRMUSICCMUSIC

MUSICMVDS


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0 5 10 150

20

40

60

80

100

120

140

160

180Estimated DOAS for only those regions which are speech

Frames Number

EstimatedDOA

(Degrees)


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class auditory perception

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