What is noise? White noise Impulsive noise Active noise Cancellation Car is a noisy environment: noise level between 65 and 75 db Adaptive Noise Cancellation Adaptive filter Algorithms used to adjust the coefficients of the digital filter

1. Faculty of Engineering
Telecommunication Engineering Department
Digital Speech Processing
‫الرحمي‬ ‫الرمحن‬ ‫هللا‬ ‫سم‬‫ب‬
An-Najah National University

3. Hearing Loss
Exposure to high noise levels causes hearing loss. This
loss of hearing may be temporary, permanent, or a
combination of both.
Temporary hearing loss results from exposure to short-
term loud noises. As time passes, temporary hearing loss
will disappear. Permanent hearing losses cannot be
treated.

4. Speech Interference & masking :
One cannot effectively use speech communication in an
environment in which the background noise level is too high.
Sometimes, the masking of warning shouts by background
noise is responsible for industrial accidents.

5. Types :

6. Impulse Noise
 Usually caused by Electromagnetic Interference, Scratches on the
recording disks, and ill synchronization in digital recording and
communication.
 High levels of such a noise (+200 Decibels) may damage internal
organs, while (+180 Decibels) are enough to destroy or damage
human ears.
 Impulsive sounds, such as Gun Shots, Hammer Blows, Explosions
of fireworks or other Blasts, are sounds that significantly exceed
the background sound pressure level for a very short duration.

7. White
Noise Blue
Noise
Brown
Noise
Red noise
Gray
NoisePink
Noise
Purple
Noise
Green
Noise
Orange
Noise
Black
Noise

8. Contains more energy as the frequency increases.

9.  To the human ear, Brown noise is similar to White noise but at a lower freq.
 Examples in nature include waves on the beach and some wind noise.
 Mimics the signal noise produced by Brownian motion.
 Also another name for Red noise.

10. Similar to white noise, but has been filtered to make the sound
level appear constant at all frequencies to the human ear.

11. Contains an equal sound pressure level in each octave band.
Energy decreases as frequency increases.

12.  Contains more energy as the frequency increases.
 Similar to Brown noise except that the power density increases 6 dB per
octave as the frequency increases.
 It is also known as Violet noise or differentiated white noise.

13. Green Noise : An unofficial term which can mean the mid-
frequencies of white noise, or the "background noise of the world".
Orange Noise : An unofficial term describing noise which has been
stripped of harmonious frequencies.
These bands of zero energy are centered
about the frequencies of musical notes. Since
all in-tune musical notes are eliminated, the
remaining spectrum could be said to consist
of Sour, Citrus, or “Orange" notes.

14. Contains an equal amount of energy in all frequency bands.

15. In other words, the signal contains equal power within a fixed
bandwidth at any center frequency.
Black Noise : A term with numerous conflicting definitions, but
most commonly refers to silence with occasional spikes.
White noise draws its name from white light in which the power
spectral density of the light is distributed over the visible band in
such a way that the eye's three color receptors (cone cells) are
approximately equally stimulated.

18. White noise has a variety of benefits and applications. Because
of its sound masking properties, white noise is ideal both as a
concentration aid and a relaxation aid, and is useful in a huge
range of situations.
Sleeping and Snoring Relief
 Unlike other snoring solutions, white noise doesn't work by
trying to stop snoring.
 Block snoring and other unwanted sounds, leading to deeper,
more restful sleep.
 For traffic noise, or noisy neighbors, white noise offers the
sleeping solution.

19. White Noise Benefits and Uses
Office White Noise
 White noise is used in the workplace, because real white
noise allows the brain to ignore even distracting ambient
sounds.
 White noise CDs can be played in any radio or even through
a computer's speakers, to provide personal relief from
distractions.
 Today, workplaces are adopting integrated white noise
systems, in which white noise is played evenly over a
speaker-system throughout large workspaces to provide
relief, and even some degree of speech privacy, to employees

20. http://acoustical-sound-masking.com/index.htm
Office White Noise

21. White Noise Benefits and Uses
Travel White Noise & Portable white noise
 Think of : Noisy Hotel Rooms, Plane rides.
 Portable white noise can be taken on a plane to soothe the
chatter and crying babies.
 White noise machines often have adapters available to make
them helpful on international trips -- and a white noise CD can
be taken anywhere a portable cd player can go.

22. White Noise Benefits and Uses
White Noise For Infants
 Often there is a sudden sound : a slamming door, music, a
raised voice, or the TV , that disturbs a sleeping baby.
 White noise for baby is a very popular solution for babies and
young children.
 Perfectly safe, white noise for infants is designed to block
harsh and unfriendly noises.
 In this way, white noise can be used to help create a safe and
comforting environment for infants.
 There are special varieties of white noise ("baby white noise")
that featuring soothing sounds.

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24. Sound Masking Noise Cancellation

25. The addition of natural or artificial sound ( such as or pink
noise) into an environment to cover up unwanted sound by
using auditory masking.
Mechanisms of masking is
Suppression.
This happens because the
original neural activity
caused by the first signal is
reduced by the neural
activity of the other sound.

27. In air-to ground communications
between a pilot and the control
tower. Since there is often a large
amount of engine and wind noise
within the cockpit of the fighter
aircraft, communication is often a
difficult problem.
However, If a secondary microphone
is placed within the cockpit of an
aircraft, then one may estimate the
noise that is transmitted and when
the pilot speaks into the microphone, and subtract this estimate from
the transmitted signal ,thereby increasing the signal to noise ratio.

29.  d(n) : Desired Voice
 V1(n) : Noise will be added to the desired Voice
 V2(n) : Noise measured by a secondary sensor used to estimate V1(n)
 X(n) = d(n) + V1(n) : Noisy corrupted Voice
 V1
^
(n) : Estimated Noise using wiener filter
 𝑑^(n) = X(n) - V1
^
(n) : Estimated Desired Voice

30.  𝑅v2 : Autocorrelation matrix of v2(n).
 𝑟v1v2 : Vector of cross-correlation between the Noise V1(n) and
wiener filter input , V2(n) .
𝑟v1v2(k) = E{ V1(n) V2(n-k)}
= E{ [ x(n) – d(n) ] V2(n – k ) }
= E{X(n) V2(n – k) } – E { d(n) V2(n –k ) }
If we assume that v2(n) is uncorrelated with d(n) ,then the second
term is zero and the cross-correlation becomes
𝑟v1v2(k)= E{x(n) V2(n –k)}= 𝑟xv2(k)
 There for the Wiener- Hopf equation is

32. Questions ?