Active Noise Cancellation

Ankit Sanjay Shah1 et al. Int. Journal of Engineering Research and Applications www.ijera.com
ISSN: 2248-9622, Vol. 6, Issue 5, (Part - 2) May 2016, pp.48-51
www.ijera.com 48 | P a g e
Active Noise Cancellation
Ankit Sanjay Shah1
, Mohnish Sunil Pophale2
, Chaitanya Sunildatta Prabhune3
Department1-3
: Electronics & Telecommunication Organisation1-3
: MIT College of Engineering
City, Country1-3
: Pune, India
Project Guide : Prof. Y. K. Subbarao Assistant Professor (Electronics & Telecommunication)
Organisation : MIT College of Engineering City, Country : Pune, India
I. INTRODUCTION
Communication is an integral part of daily life for
conveying information. But, what comes with the
information is various types of unwanted signals,
called as NOISE. Noise pollution or Noise disturbance
is the disturbing or excessive noise that may harm
humans as also animals. The source of most outdoor
noise worldwide is due to machines and transportation
systems i.e. motor vehicles, aircraft, trains etc. (Refer
Fig. 1.1). Outdoor noise can often be summarized by
the term “Environmental Noise”. Noise pollution can
also be caused due to inefficient infrastructural
facilities in cities, for instance, side-by-side industrial
and residential areas. There are various sources of
indoor noise such as those caused by machines,
building activities, and music performances,
especially in some workplaces. Noise-induced hearing
loss can be caused by outside (e.g. trains) or inside
(e.g. music) noise.
Fig. 1.1 Sources of noise
In this paper, we have used Simulink model to get the
desired noise cancelled signal.
II. REVIEWOF THE RELATED
LITERATURE
The idea for this project was inspired from the
SILENTIUM products(Ref. fig. 2.1) & „Noise
Cancelling Headphones‟ by Sony, BOSE, Panasonic
etc., which are becoming very popular in recent years.
Noise cancellation makes it possible to enjoy music
without raising the volume excessively.
Workshop S-CubeKit S-ChipTM
Fig. 2.1 Silentium Products (Ref. [6])
Noise cancellation is of major concern in the acoustic
industries also. The noise of blowers in a ventilation
system is carried over a few kilometres through a duct.
This affects the acousticenvironment. Use of passive
silencers and baffles alone does not solve this problem
as, only the high frequency noise components are
cancelled out, while the lower frequency components
are reverberated inside the ventilation
duct.Accompanying the passive silencers, an active
noise silencer is required in order to cancel these noise
components.
RESEARCH ARTICLE OPEN ACCESS
ABSTRACT
In this work, we develop a new approach to active noise cancellation. Theoretically, we use a 180 degree phase
shift of the noise, i.e. generate an anti-noise, to cancel the original signal. Here, we have designed FIR filter
which is driven by the input signal and has the noise signal as the feedback, and output of which is the required
result. The active noise control system contains an electro-acoustic device that cancels the unwanted audio
signal by generating an anti-noise of equal amplitude and opposite phase. The original, unwanted sound and the
anti-noise combine acoustically, resulting in the cancellation of both sounds. The effectiveness of cancellation
of the unwanted signal depends on the accuracy of the amplitude and phase of the generated anti-noise.
Keywords: Active Noise Cancellation, LMS algorithm, FIR filter, Simulink, DSP kit, Silentium.

However, in India, only a few of such projects are
implemented practically (on hardware). If such
products are imported, they cost very high (approx.
₹1 lakh). This definitely does not help the Indian
economy. Hence, there is an ardent need of
manufacturing such product in India, after
consideration of factors such as the effectiveness,
reliability and the most importantly, its cost.
III. BLOCK DIAGRAM
Refer Fig.3.1. for block diagram
Fig 3.1. System Block Diagram
Fig. 3.1 Represents the block diagram of the system to
be implemented. The system input is through a
Microphone and is passed to the Analog to Digital
Converter (ADC), which converts the analog input to
digital samples at a sampling rate of 8 kHz.
The first lowpass filter designed based on FIR
algorithm is used to limit data frequency below cut-off
frequency.Frame Subtractor block is used to find the
difference between successive frames, i.e., Z[n+1]-
Z[n]. The framegenerated is a vector of size “m x n”.
This gives us the reference signal. The original and the
reference signalare added out-of-phase to obtain the
noise signal, which is then used as feedback for the
adpative algorithm.The adaptive filter block adapts the
filtered weights as per the feedback it receives.
The second lowpass filter is used as a precautionary
measure to avoid any addition of internal noise due to
hardware limitations. The Digital to Analog Converter
(DAC) converts the digital samples of output to
analog output at a reconstruction sampling rate of 8
kHz.
IV. LIST OF COMPONENTS
A. HARDWARE REQUIREMENTS
DSP kit – TMS320C6713
Microphone
Speaker
Power supply
B. SOFTWARE REQUIREMENTS
Matlab R2014a
Simulink
Code Composer Studio v3.1
V. SYSTEM DESIGN&
IMPLEMENTATION
Refer Fig.5.1 for System Design diagram
Fig. 5.1, representing the system design, consists of
acoustic environment selector switch. It allows to
provide the interna as well as external input. All the
signals are stored in workspace and they can be played
by clicking the buttons provided.
The adaptive algorithm block (Normalized Least
Mean Square) consists of five ports namely input,
desired, stepsize, adapt and reset.
Fig.5.1. Simulink model for Active Noise
Cancellation using Least Mean Square Algorithm (Ref
[5])
Input: The original input of the system is through an
external microphone connected to the system at this
port.
Desired: The reference signal is fed through this port.
Step-size: It defines the rate of adaptaion of the
adaptive filter, generally denoted by µ.
Adapt: It is used to make the adaptive algorithm ON
or OFF. It is an optional port.
Reset: It resets the entire system to take the original
input again and start the process afresh.
In most of the practical applications, Adaptive filters
areused and are preferred over fixed digital filters
because adaptivefilters have the property of adjusting
its frequencyresponse and allowing the filter to adapt
to the response as theinput signal characteristics vary.
The general configuration of an Adaptive Filter is
shown in Fig. 5.2.
It has two inputs: the primary input d(n),
whichrepresents the desired signal plus noise, and
thereference signal x(n), which is the noise to be
filtered out ofthe system.

Fig. 5.2 Adaptive Filter Algorithm Block Diagram
The goal of adaptive filtering systems is to reduce the
noiseportion, and to obtain the uncorrupted signal
which is desired. In orderto achieve this, a reference
of the noise signal, called reference signal x(n), is
needed. However, the reference signal istypically not
the same as the noise present in theprimary signal; it
may be different in amplitude, phase or
frequency.Therefore, the reference signal cannot be
simply subtracted fromthe primary signal to obtain the
desired signal at the output.
A. Least Mean Square algorithm
The LMS algorithm is a gradient based algorithm that
uses gradient vectors of the filter tap weights to
converge to the optimal weigner solution. With every
iteration, the weights of the adaptive filter get updated,
which can be calculated by the following equation:
w(n+1)= w(n) + 2 µ e(n) x(n)
where, x(n) is the input vector,
w(n) represents the co-efficients of the FIR filter,
µ is the stepsize that decides the time of convergence.
If the value of µis too small, the time required for the
convergence will be too long; if the value is too large,
the filter may become unstable and the output can
diverge.
B. Normalised Least Mean Square Algorithm
To overcome the drawback of Least Mean Square
algorithm in case of the large stepsize, normalized
LMS algorithm is used in which the stepsize can be
calculated as follows:
where, α is the NLMS adaption constant, that is used
to optimize the convergence rate of the algorithm and
should satisfy the condition 0<α< 2. „c‟ is a constant
term used for normalization, which is always less than
1.
The filter weights using NLMS algorithm are updated
by the equation:
Fig 5.3 Simulink Model of filter used in Fig 5.1 (Ref. [5])
In fig 5.3, the input is given to system from the
external microphone. This audio input is then filtered
out to allow only frequencies below 3 kHz. This is
then given to frame subtractors to get the reference
signal which is the noise signal.
The reference signal and the original signal are then
added out of phase to give us the noise signal which is
given to digital filter and further to the adaptive
algorithm block.
The filter selector switch is used to select from two
filter options available:
1) Bandpass Filter
2) Lowpass Filter
Both the filter designs are based on FIR principle of
order 39. The Bandpass filter is designed so as to pass
frequencies in between 0.3 & 0.5 (normalised). The
lowpass filter is designed so as to pass frequencies
below 0.25 (normalised).
The numerator coefficients found out are passed to
Digital Filter block along with the signal to be filtered
out. The output of this filter is given to LMS
algorithm block for further processing.
V. FUTURE SCOPE
This system can be incorporated at workplaces such as
schools and colleges, industrial workshops as well as
residential areas near airports, market places etc.
Other adaptive algorithms may be used to enhance the
efficiency of the system. Combination of existing
technology and our system may bring out a new
invention which is efficient and cost effective system
in the near future.

REFERENCES
[1] Raj Kumar Thenua and S. K. Agrawal,
“Hardware Implementation of Adaptive
Algorithms forNoise Cancellation,”
International Journal of Information and
Electronics Engineering, Vol. 2, No. 2,
March 2012.
[2] Alan V. Oppenheim, Ehud Weinstein, Meir
Feder, Kambiz C. Zangi, Dan Gauger,
“Single-Sensor Active Noise Cancellation,”
IEEE transactions on speech and audio
processing, vol. 2, no. 2, April 1994.
[3] Vaibhav Narula, Mukul Sagar, Pranab
Joshi,Puneet S. Mehta,Sudhanshu Tripathi,
“Real-Time Active Noise Cancellation with
Simulink and Data Acquisition Toolbox,”
Proc. of Int. Conf. on Advances in Electrical
& Electronics 2011.
[4] Texas Instruments, “Design of Active Noise
Control Systems with the TMS320 family,”
Application Report 1996.
[5] Available at http://mathworks.com
[6] Silentium http://silentium.com

Active Noise Cancellation

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