Digital Signal Processing - Vibrations & Acoustics


Digital Signal Processing Lab
The Digital Signal Processing (DSP) Lab is under the under the management of Dr. Sen-Maw Kuo.  The main research emphasis is focused on real-time DSP applications.  The projects being conducted by the lab are primarily active noise control (ANC) and active vibration control (AVC) systems.  

Active Noise Control (ANC)
ANC systems are used to cancel unwanted noise.  ANC systems work on the principle of superposition; an anti-noise signal of the same magnitude and opposite phase is generated to cancel the unwanted primary noise. Typically, the primary noise is picked up by a microphone, and sent to the DSP and an anti-noise is produced to cancel with the original noise. ANC systems support a wide variety of applications; the applications pursued in this laboratory are given below.

Snore ANC System
Snore is generated during sleep due to obstruction in the upper airway. Research indicates that snoring is not only very annoying but also has significant daytime consequences to the bed partner. To provide an effective, harmless and comfortable solution, feed forward ANC systems have been designed to reduce the volume level of the snore being heard by the bed partner. TMS320C32 DSP is being used to generate the anti-snore. Various configurations of the ANC systems are being explored to improve the snore cancellation.

Figure 1: Demo setup for Snore ANC

Global ANC System
The noise on a factory floor can be loud, distracting, and hazardous.  To reduce the overall noise on a factory floor from a machine, a global ANC system is needed.  The local ANC systems used in the Snore and Incubator Systems cancel the noise at a particular location.  To achieve the global cancellation the sound must be focused to a point or small region.  This is done by partial surrounding the machine in an acoustical barrier and suspending a dome above.  A local ANC system is placed between the acoustical barrier and the dome in the region that the sound is focused to cancel the maximum amount of noise. The experimental setup has demonstrated significant attenuation of low frequencies. 

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Figure 2:  Demo setup for Global ANC

Incubator ANC System
Pre-term babies are very fragile and must cope with their environment with immature organ systems. Their auditory, visual and central nervous systems are the last to mature. These last stages of development occur in part, during the time the premature baby is in the incubator. It has been recognized that noise levels in Neo-natal ICUs and inside incubators are harmful for the development of these babies. This has given rise to a need for active noise control in such systems.

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Figure 3:  Demo setup for Incubator ANC

Noise Masking using Psychoacoustics
This research delves into a new research area of noise masking for ANC systems.  Soothing audio is used to mask the residual snore noise which is still annoying to the human ear in a very quiet environment. To reduce the overall volume level, the masker is passed through a psychoacoustic processor that takes advantage of the limitations in the human auditory system.  As a further step towards improving the system performance, off-line and on-line modeling of secondary paths are being implemented using soothing audio.

Active Vibration Control (AVC)
Active vibration control works on the same principle as ANC, but to cancel vibration in structures. AVC systems use shakers and accelerometers in place of speakers and microphones in ANC systems.  The following projects are applications of AVC that are currently being worked on in the DSP lab. 

AVC Seat
Whole-body vibration (WBV) has been attributed to lower back pain, fatigue, and discomfort.  An active vibration control seat is being designed to reduce the WBV experienced by the operators of agricultural, construction, forestry, and mining equipment.    

ROCK Project:  Vibration Isolation Platform
The Army Rapid Optimization of Commercial Knowledge Project is based out of EIGERlab in Rockford, IL.  This project is designed to create new manufacturing technologies.  The DSP lab is involved with designing a vibration isolation platform for micro milling.  The platform will use AVC to reduce low frequency vibration.  By using AVC, the platform will be very light weight and mobile compared to the two ton tables that are currently used to absorb the vibration. 

College of Engineering and Engineering Technology
Northern Illinois University
DeKalb, IL 60115-2854