ACTIVE NOISE CONTROL
• Active noise control (ANC) has received much attention in recent
years. In an ANC system, a secondary source is introduced to
generate anti-noise of equal amplitude but of opposite phase with
reference to the primary noise. ANC techniques can be utilized to
extract a signal buried in noise or to cancel unwanted noise.
WHAT IS NOISE ?
• Noise means any unwanted sound.
• Unwanted waveforms that can interfere with communication.
WHAT IS ACTIVE NOISE CANCELLATION ?
• Method for reducing unwanted sound by the addition of a
second sound specifically designed to cancel the first.
WHAT IS ADAPTIVE FILTER ?
• Adjust themselves to an ever-changing environment.
• Changes its parameters so its performance improves
through its surroundings.
WHY WE USE ADAPTIVE FILTER?
• Because some parameters of the desired processing operation are not
known in advance or are changing.
• A filter which adapts itself to the input signal given to it.
• It is non-Linear and Time Variant.
• The adaptive filtering system contains four signals: reference
signal, d(n), input signal, x(n), output signal, y(n), and the error
signal, e(n). The filter, w(n), adaptively adjusts its coefficients
according to an optimization algorithm driven by the error
y(n) w n x n
( ) ( )
• Least Mean Squares Algorithm (LMS) widely used Adaptive
algorithm for noise cancellation.
• The Least Mean Squares Algorithm (LMS) updates each
coefficient on a sample-by-sample basis based on the error
w (n 1) ( ) ( ) ( ) k w n e n x n k k
• μ (mu) is critical is Convergence Coefficient.
• μ is set by trail and error for each Application.
APPROACHES OF ANC
• Reference noise and
cancelled noise are used
• 2 inputs and 1 output
• Only cancelled noise are
used – one input and one
n of S(z),
Path , S(z)
• Coherent input is captured,
filtered and feed into LMS
•Estimation of the secondary
path transfer function is
obtained by identification
• Implement it on Hardware.
• Use Laboratory Duct model technique to design Adaptive
Active Noise Cancellation System.
• Active noise cancellation with a fuzzy adaptive filtered-X
• Noise Cancellation Headsets (headphone)
• Bikes and cars.
• Space satellite antennas.
• Jet engines and heavy machinery.
• Noise-Muter and more..
• Adaptive recurrent fuzzy neural networks for active noise control
• Digital Signal Processing : Principles, Algorithms and
Applications 4e by Proakis and Manolakis.
• Signal Processing for Active Control by Stephen Elliott.