ACTIVE noise control (ANC)
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05-10-2010, 12:32 PM

.pdf   sub_band_adaptive_algorithm.pdf (Size: 801 KB / Downloads: 181)
A New Delayles s Subband Adaptive Filtering
Algorithm for Active Noise Control Systems

Ali A. Milani, Student Member, IEEE, Issa M. S. Panahi, Senior Member, IEEE, and
Philipos C. Loizou, Senior Member, IEEE


Subband adaptive filtering (SAF) techniques play a
prominent role in designing active noise control (ANC) systems.
They reduce the computational complexity of ANC algorithms,
particularly, when the acoustic noise is a broadband signal and the
system models have long impulse responses. In the commonly used
uniform-discrete Fourier transform (DFT) -modulated (UDFTM)
filter banks, increasing the number of subbands decreases the
computational burden but can introduce excessive distortion,
degrading performance of the ANC system. In this paper, we propose
a new UDFTM-based adaptive subband filtering method that
alleviates the degrading effects of the delay and side-lobe distortion
introduced by the prototype filter on the system performance.
The delay in filter bank is reduced by prototype filter design and
the side-lobe distortion is compensated for by oversampling and
appropriate stacking of subband weights. Experimental results
show the improvement of performance and computational complexity
of the proposed method in comparison to two commonly
used subband and block adaptive filtering algorithms.
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09-05-2011, 11:03 AM

Presented by:
Manish Gaur

.pptx   ANC.pptx (Size: 3.01 MB / Downloads: 77)
Active Noise Control

How does Active Noise Cancellation (ANC) works ?
Basic principles by introducing a canceling anti-noise signal that has the same amplitude but the exact opposite phase and resulting a reduction noise signal
Active control is sound field modification, particularly sound field cancellation, by electro acoustical means.
A control system drives a speaker to produce a sound field that is an exact mirror-image the offending sound (the "disturbance"). The speaker thus "cancels” the disturbance, and the net result is no sound at all.
As an alternative to passive noise cancellation techniques and often in combination with them, active noise cancellation (ANC) offers an effective solution in certain applications.
In contrast to passive techniques, ANC systems are small, portable, adjustable to different environments, and less costly.
There are main four parts of active control system-:
The plant is the physical system to be controlled; typical examples are a headphone and the air inside it, or air traveling through an air-conditioning duct.
Sensors are the microphones. accelerometers, or other devices that sense the disturbance and monitor how well the control system is performing.
Actuators are the devices that physically do the work of altering the plant response; usually they are electromechanical devices such as speakers or vibration generators.
The controller is a signal processor (usually digital) that tells the actuators what to do, the controller bases its commands on sensor signals and, usually, on some knowledge of how the plant responds to the actuators.
Traditionally, two basic methods are used in ANC systems-:
Adaptive cancellation system.
Active noise cancellation system.
Noise is detected by one or more microphones. The system then adapts itself to generate anti-noise waveform which minimizes the residue (mic.) noise.
Adaptive cancellation can be used for both periodic and non-periodic noise.
When used with non-periodic noise the adaptive method is limited because it usually involves a prediction or an estimation process.
Active noise cancellation system is based on the synthesis method.
This involves sampling and storing one or more noise cycles .
based on this information received an actual anti-noise waveform is generated to suppress the noise.
The noise cancellation circuit works by detecting the noise of the surrounding environment using a microphone attached to the earpieces of the headset.
The system is quite versatile with regards to the type of noise it will attenuate.

Phones in a factory work in a very noisy environment. Noise of different machines and equipment is also transmitted in the phone line.
Active noise control is a possibility for efficient noise suppression, even if the spectra of the speech and the noise are overlapped in the frequency domain.
Propeller-driven airplanes generate a high-level noise which is disturbing for the passengers

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