Dale J. Shpak

Method and apparatus for automatic volume control in an audio system

An audio system (100) is provided with improved adaptive filter (206) to automatically adjust signal gain depending on the ambient noise level. The original music signal passes through a normalized adaptive filter (206), and is subtracted from the ambient room signal detected by a microphone (120), resulting in an error signal that is an estimate of the ambient noise. The error signal is used to update a set of adaptation coefficients so that the normalized adaptive filter more accurately simulates the room transfer function, resulting in an better estimate of the ambient noise. The audio system (100) is calibrated automatically upon initial use to determine adaptation coefficients and noise threshold level to prevent runaway gain. System parameters are adjusted using a controller (124) with a user-friendly interface (400).

A generalized Remez method for the design of FIR digital filters

A generalized Remez method for the design of finite impulse response (FIR) filters is proposed. The method is based on a new problem formulation which largely eliminates certain difficulties brought about by an undetermined approximating polynomial. The new method can be used to design maximal-ripple (MR), extra-ripple (ER), and weighted-Chebyshev filters satisfying prescribed specifications, and, with the addition of some simple techniques, filters can be designed that are free from transition region anomalies. The method incorporates a new initialization strategy and a selective search technique to reduce the amount of computation needed to carry out a design. Extensive experimental results show that the new method is robust and at least as efficient as existing methods for the design of weighted-Chebyshev filters. For MR as well as ER filters, the new method is both robust and very efficient. >

A method for the optimal pattern synthesis of linear arrays with prescribed nulls

A new L/sub /spl infin// optimal method for the synthesis of equispaced linear array functions with asymmetrical far-field pattern functions is proposed. This iterative method provides for the exact specification of the beam width, while at the same time allowing for the specification of the relative levels of individual sidelobes by index or as a function of bearing (e.g., angularly-extended nulls), as well as the realization of specified narrowband nulls. The resulting array factors are optimal in the weighted L/sub /spl infin// sense and, in general, have complex coefficients. This new Remez-type method employs multiple objective functions to provide the degrees of freedom that are required for exact null placement. Examples which demonstrate the design flexibility offered by the method are included for various sum and difference patterns, including superdirective and shaped-beam arrays.

Improved Design Method for Nearly Linear-Phase IIR Filters Using Constrained Optimization

A new optimization method for the design of nearly linear-phase IIR digital filters that satisfy prescribed specifications is proposed. The group-delay deviation is minimized under the constraint that the passband ripple and stopband attenuation are within the prescribed specifications and either a prescribed or an optimized group delay can be achieved. By representing the filter in terms of a cascade of second-order sections, a non-restrictive stability constraint characterized by a set of linear inequality constraints can be incorporated in the optimization algorithm. An additional feature of the method, which is very useful in certain applications, is that it provides the capability of constraining the maximum gain in transition bands to be below a prescribed level. Experimental results show that filters designed using the proposed method have much lower group-delay deviation for the same passband ripple and stopband attenuation when compared with corresponding filters designed with several state-of-the-art competing methods.

Hardware implementation of a wavelet based image compression coder

A VLSI architecture designed to perform real-time image compression using wavelets is described. The two basic modules of the architecture are a 2-D wavelet transform generator and a coder based on the SPIHT algorithm for lossy image compression. A folded architecture is proposed for computing the 2-D wavelet transform. The architecture uses 3 parallel computational units and 2 storage units. The hardware for the SPIHT coder uses 2 content addressable memories and 3 random access memories. The designs are modular and can easily be extended for different levels of wavelet decomposition and filter lengths. The derived architecture has been functionally verified for an 8/spl times/8 image size by simulating its VHDL code using Mentor Graphics.

Design of IIR Digital Differentiators Using Constrained Optimization

A new optimization method for the design of fullband and lowpass IIR digital differentiators is proposed. In the new method, the passband phase-response error is minimized under the constraint that the maximum passband amplitude-response relative error is below a prescribed level. For lowpass IIR differentiators, an additional constraint is introduced to limit the average squared amplitude response in the stopband so as to minimize any high-frequency noise that may be present. Extensive experimental results are included, which show that the differentiators designed using the proposed method have much smaller maximum phase-response error for the same passband amplitude-response error and stopband constraints when compared with several differentiators designed using state-of-the-art competing methods.

A flexible optimization method for the pattern synthesis of equispaced linear arrays with equiphase excitation

A synthesis method is proposed for linear arrays having equiphase excitation currents. In addition to allowing for the exact specification of the beamwidth and for the specification of individual sidelobe levels by index or as a function of bearing (e.g., angularly extended nulls), multiple deep narrow nulls can be specified at arbitrary bearing angles. The method is suitable for the design of broadside or endfire arrays with sum or difference patterns and can also be used for the design of superdirective arrays with good radiation efficiencies and sensitivity properties. For computational efficiency, the method uses a new constrained multivariable Remez-type L/sub infinity / approximation technique. >

L -infinity norm design of linear-phase robust broadband beamformers using constrained optimization

A new method for the design of linear-phase robust far-field broadband beamformers using constrained optimization is proposed. In the method, the maximum passband ripple and minimum stopband attenuation are ensured to be within prescribed levels, while at the same time maintaining a good linear-phase characteristic at a prescribed group delay in the passband. Since the beamformer is intended primarily for small-sized microphone arrays where the microphone spacing is small relative to the wavelength at low frequencies, the beamformer can become highly sensitive to spatial white noise and array imperfections if a direct minimization of the error is performed. Therefore, to limit the sensitivity of the beamformer the optimization is carried out by constraining a sensitivity parameter, namely, the white noise gain (WNG) to be above prescribed levels across the frequency band. Two novel design variants have been developed. The first variant is formulated as a convex optimization problem where the maximum error in the passband is minimized, while the second variant is formulated as an iterative optimization problem and has the advantage of significantly improving the linear-phase characteristics of the beamformer under any prescribed group delay or linear-array configuration. In the second variant, the passband group-delay deviation is minimized while ensuring that the maximum passband ripple and stopband attenuation are within prescribed levels. To reduce the computational effort in carrying out the optimization, a nonuniform variable sampling approach over the frequency and angular dimensions is used to compute the required parameters. Experiment results show that beamformers designed using the proposed methods have much smaller passband group-delay deviation for similar passband ripple and stopband attenuation than a modified version of an existing method.

Maximizing the Signal-to-Alias Ratio in Non-Uniform Filter Banks for Acoustic Echo Cancellation

A new method for designing non-uniform filter-banks for acoustic echo cancellation is proposed. In the method, the analysis prototype filter design is framed as a convex optimization problem that maximizes the signal-to-alias ratio (SAR) in the analysis banks. Since each sub-band has a different bandwidth, the contribution to the overall SAR from each analysis bank is taken into account during optimization. To increase the degrees of freedom during optimization, no constraints are imposed on the phase or group delay of the filters; at the same time, low delay is achieved by ensuring that the resulting filters are minimum phase. Experimental results show that the filter bank designed using the proposed method results in a sub-band adaptive filter with a much better echo return loss enhancement (ERLE) when compared with existing design methods.

Synthesis of Linear and Planar Arrays With Minimum Element Selection

A new method for the synthesis of linear and planar arrays having prescribed beamwidth and sidelobe levels and a minimum number of elements is proposed. In the method, the number of elements in an array is minimized while constraining the amplitude-response error in the mainlobe region, the attenuation in the sidelobe region, and the array dimensions. An iterative constrained optimization method is used where the amplitude-response error is linearly approximated at each iteration while concurrently minimizing a re-weighted L1 norm of the array coefficients. To ensure robustness of the array, we constrain a sensitivity parameter, namely, the white noise gain, to be above a prescribed level. Furthermore, the method also provides the additional flexibility of controlling the array dimensions, symmetry properties, and element positions of the array. Two variants have been developed: In the first variant, both the array coefficients and the positions of the elements are optimized; in the second variant, only the array coefficients are optimized while the elements are fixed at predefined positions. Experimental comparisons with several state-of-the-art competing methods show that the proposed method provides greater flexibility of controlling the robustness, beampattern response error, array dimensions, and element positions while at the same time the number of elements is less than or equal to that of the competing methods.