Noise cancellation

E.P.P.A. Derks, B.A. Pauly, J. Jonkers, E.A.H. Timmermans and L.M.C. Buydens, Adaptive noise cancellation on inductively coupled plasma spectroscopy. Chemom. Intell. Lab. Syst., (1998) in press. 

The major advantage of this dramatic time reduction lies in the ability to scan the sample repeatedly, combine the relaxation-decay patterns collected from each scan, and then perform a Fourier transform upon the final composite relaxation-decay pattern. This technique, in essence, increases the spectral sensitivity by allowing the NMR signals acquired from each scan to be constructively added to each other while the noise cancels itself de-con structively. This approach greatly increases the sensitivity of the instrument and allows NMR experiments to be performed on samples that have low concentrations of the desired nucleus (i.e., for 31P, 20 mg of P/L is a feasible concentration with instrument time of hours to a few days). 

Figure 6.18 Block diagram of an adaptive noise-cancellation system.

The performance of a head-mounted two-microphone adaptive noise-cancellation system was investigated by Weiss [Weiss, 1987] and Schwander and Levitt [Schwander and Levitt, 1987]. In this system, an omnidirectional microphone was used for the speech signal and a rear-facing hypercardioid microphone mounted directly above the speech microphone was used for the noise reference. In a room having a reverberation time of 0.4 sec, this system improved the speech recognition score to 74 percent from 34 percent correct for the unprocessed condition for normal-hearing listeners given... 

Small voltage generators (sensors) car crash sensors to activate air-bags, noise cancellation, active suspension for cars, anti- knock sensor for i.c. engines, liquid level sensing, etc. 

If hundreds of individual runs are averaged, the background noise cancels. 

Fig. 6.1.15 Timing of correlated double sampling (CDS) a) circuit reset, b) sampling noise cancellation, c) sensing...

Performance at Baseband with a Novel Electronic Noise Canceller." SPIE 1435 (1991) 298-309. 

It is often necessary to earth one end of the screen for practical reasons. If the end at Ag in Figure 13.15 is earthed then the earth path resistance Rg shunts the screen completely and some of the screen current will flow along the earth path. This will unbalance the core and screen currents and so noise cancellation will not occur. A noise voltage will appear in the core circuit. Earthing the screen at the end Bg overcomes this difficulty because the positive channel of the amplifier is a virtual earth. In some cases the connection at Bg is made at a clean or instrument earth if the receiving device has only one channel or input terminal (the chassis or framework would be the second channel or... 

Allen, J.N., Abdel-Aty-Zohdy, H.S., Ewing, R.L. Electronic nose inhibition in a spiking neural network for noise cancellation. In Proceedings of the 2004 IEEE Symposium on Computational Intelligence in Bioinformatics and Computational Biology, CIBCB 2004, pp. 129-133 (2004)... 

Berghe, J.V. and Wouters, J., An adaptive noise canceller for hearing aids using two nearby microphones, The Journal of the Acoustical Society of America, 103,1998, 3621. 

Active HeoriM ProtecHoe Devices—are noise-attenuating helmets that provide active noise cancellation, communications features, and attenuation. They reduce noise by introducing destructive cancellation that applies opposite-phase sound waves at the ear. Some are designed for hearing protection and others for one- or two-way communication. 

As the biomolecular interaction delivers a very weak electronic signal, integrated amplification and noise canceling are often... 

Figure 8.18 shows a commonly used circuit for power line noise cancellation. Figure 8.19 shows three situations of power line capacitively coupled noise voltage. Suppose first (left)... 

If you work around engines, blowers, motors, vacuums, pumps, generators, compressors, fans, etc., you need protection against low-frequency noise — noise that conventional passive earmuffs alone can t handle. Only NoiseBuster Active Noise Reduction Safety Earmuffs combine high-performance passive earmuffs with advanced active noise cancellation technology for the most comprehensive hearing protection available to industry today. 

I have a theory (as opposed to a dream) that Heaven is a three-class Boeing 111. You can sit in a narrow seat that does not recline and eat chicken-like substances next to a screaming baby in coach class. Alternatively, you can sit in a slightly wider seat that reclines a bit more and eat a beef-like substance in business class. But the goal is to spend eternity in first class—specifically, Singapore Airlines first class. Here your seat reclines to a completely flat position, and there is a power outlet, personal video player, wireless access to the Internet, and noise-canceling headphones. There are also chefs, not microwave ovens. 

Noise. One system for abating unwanted sound is active noise control. The first successful application of active noise control was noise-canceling headphones,... 

Microphones in this group include hand-held noise-canceling units for mobile communications and industrial plant operations, handset and headset-boom microphones for intercom and order wire circuits, and public address microphones. Each user group has its own particular set of needs, met through variations on a few basic designs. 

Adaptive noise canceling makes use of an auxiliary or reference input in addition to the noisy signal from the primary sensor. If a reference for the noise is desired, the auxiliary microphone is placed at a position in the noise field where the signal is weak or undetectable. This scheme operates on the basis of two main assumptions ... 

The earKest work on adaptive noise cancelers can be traced to the mid 1960s to Kelly of Bell Telephone Laboratories, who first proposed the use of an adaptive filter for echo cancellation of speech signals. Kelly s contribution is cited in the bookby Haykin (1991). Widrow et al. (1975) extended the concept and built a device to cancel 60-Hz interference at the output of an electrocardiograph amplifier and recorder. Lim and Oppenheim (1979) discuss the use of adaptive noise cancellation on speech and find that, at some SNR, the technique actually decreases the intelligibility of the speech signal. 

In active noise cancellation, the noisy input signal is adaptively filtered to produce a signal that is supplied to a canceling microphone. The output from the canceling microphone destructively interferes with the noise (Oppenheim et al, 1994). A block diagram appears in Fig. 12.99. 

Oppenheim, A.V., Weinstein, E., Zangi, K.C., Feder, M., and Gauger, D. 1994. Single-sensor active noise cancellation. IEEE Trans. Speech and Audio Processing 2(2) 285-290. 

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