Abstract: In a frequency-domain excision system for a wide band receiver, a window function is applied to blocks of received signal samples and a transform function is applied to the windowed blocks. Each block of frequency-domain coefficients from the transform function is morphologically filtered to generate a threshold function representing an estimate of the spectrum of the desired wide band signal, and a non-linear gain function is applied to the coefficients. The gain function has a fixed-gain region for input values less than a threshold value from the threshold function, an excision region for input values greater than a multiple of the threshold value, and a soft limiting region between the fixed-gain region and the excision region. The inverse transform is performed on the excised blocks of coefficients, and an overlap-eliminating central portion of the inverse of the window function is applied to the resulting blocks of signal samples.

Abstract: In a frequency-domain excision system for a wide band receiver, a window function is applied to blocks of received signal samples and a transform function is applied to the windowed blocks. Each block of frequency-domain coefficients from the transform function is morphologically filtered to generate a threshold function representing an estimate of the spectrum of the desired wide band signal, and a non-linear gain function is applied to the coefficients. The gain function has a fixed-gain region for input values less than a threshold value from the threshold function, an excision region for input values greater than a multiple of the threshold value, and a soft limiting region between the fixed-gain region and the excision region. The inverse transform is performed on the excised blocks of coefficients, and an overlap-eliminating central portion of the inverse of the window function is applied to the resulting blocks of signal samples.

Abstract: By this invention, there is provided a process for producing crystalline 4,7.beta.-dimethyl-4-aza-5.alpha.-cholestan-3-one of structural formula (I) from 4,7.beta.-dimethyl-4-aza-5.alpha.-cholestan-3-one oil. ##STR1## This crystallization process of the present invention comprises crystallization of the oil optionally containing residual solvent with vigorous but controlled agitation. Preferably, this crystallization process is carried out at select and controlled temperatures. Further, 4,7.beta.-dimethyl-4-aza-5.alpha.-cholestan-3-one has been found to exist in at least two novel polymorphic nonsolvated forms, herein referred to as Form I and Form II. Form I can be prepared pure by careful control of the crystallization process.