Blind identification of source signals is studied from both theoretical and algorithmic aspects. A mathematical structure is formulated from which the acceptable indeterminacy is represented by an equivalence relation. The concept of identifiability is then defined. Two identifiable cases are shown along with blind identification algorithms. The performance of FOBI (fourth-order blind identification), EFOBI (extended FOBI), and AMUSE algorithms is evaluated by some heuristic arguments and simulation results. It is shown that EFOBI outperforms the FOBI algorithm, and the AMUSE algorithm performs better than EFOBI in the case of nonwhite source signals. AMUSE is applied to a speech extraction problem and shown to have promising results. >

Indeterminacy and identifiability of blind identification

Speech recognition in adverse environments

A consistent framework is presented for the calculation of the optimal performance of feedforward and feedback control systems in attenuating random disturbances. In both cases, the optimization problem is transformed into a quadratic form using an internal model of one part of the physical system under control. The resulting architecture for the feedback controller is known as internal model control (IMC) and is widely used in the H/sub /spl infin// control literature. With this controller architecture, the optimum performance of a multichannel feedback system can be readily calculated using the quadratic optimization techniques already developed in the sampled time domain for multichannel feedforward control. The robustness of the stability of such a feedback controller to changes in the plant response can be separately assessed using a generalization of the complementary sensitivity function, which has a particularly simple form when IMC is used. The stability robustness can be improved by incorporating various forms of effort weighting into the cost function being minimized, some of which are already used for adaptive feedforward controllers. By way of example, the performance is calculated of both feedforward and feedback controllers for the active attenuation of road noise in cars. The variation of performance with loop delay is calculated for both types of control, and it is found that in this example, the potential attenuation is greatest using feedback control but only if the loop delay is less than 1.5 ms.

Performance of feedforward and feedback systems for active control

Acoustic noise analysis and speech enhancement techniques for mobile radio applications

The properties of noise fields in automobile interiors are discussed with a view toward speech enhancement for voice-activated mobile telephony. The limitations on performance of adaptive noise cancellation are explained in the context of the spatial correlation properties of the noise field. A simple delay-equalized near-field array of directional microphones is analyzed and found to be effective for increasing the signal-to-noise density ratio (SNR) and reducing the reverberant distortion of the speech, without introducing any further distortion. An array of N microphones, each with a delay and weight chosen according to its distance from the speech source, is a viable solution. Such an array gives gains on the order of N over the speech band, reduces reverberation, and does not introduce waveform distortion. Experimental results confirming the predicted performance are presented. >

https://summit.sfu.ca/system/files/iritems1/5560/b15090474.pdf

Speech enhancement for mobile telephony

This paper presents some preliminary results from adaptive noise cancellation experiments performed in a fighter aircraft cockpit simulator. The sound field and noise levels used in the experiment were very much more realistic than those used in previously reported experiments and the adaptive noise cancellation was performed in real time, using man mountable, Texas Instruments TMS 380 based hardware. The results confirm earlier assertions and indicate that generally, software and "off line" simulations have yielded optimistic results.

Practical adaptive noise reduction in the aircraft cockpit environment

It has been reported that the application of broadband noise cancelling techniques to the control of aircraft cockpit noise pickup is only successful at low frequencies This effect is explained in terms of measures of the noise transmission across a standard British oxygen mask and a discussion of the spatial characteristics of the cockpit's acoustic field A theoretical prediction of the maximum noise reduction given by a single channel noise cancelling system controlling a group of independantly excited noise transmission paths is presented

P. Wheeler

Papers

Practical adaptive noise reduction in the aircraft cockpit environment

Adaptive noise reduction in aircraft communication systems