The role and selection of the filter function in Fourier self-deconvolution revisited.

Overlapped bands often appear in applications of infrared spectroscopy, for instance in the analysis of the amide I band of proteins. Fourier self-deconvolution (FSD) is a popular band-narrowing mathematical method, allowing for the resolution of overlapped bands. The filter function used in FSD plays a significant role in the factor by which the deconvolved bands are actually narrowed (the effective narrowing), as well as in the final signal-to-noise degradation induced by FSD. Moreover, the filter function determines, to a good extent, the band-shape of the deconvolved bands. For instance, the intensity of the harmful side-lobule oscillations that appear in over-deconvolution depends importantly on the filter function used. In the present paper we characterized the resulting band shape, effective narrowing, and signal-to-noise degradation in infra-, self-, and over-deconvolution conditions for several filter functions: Triangle, Bessel, Hanning, Gaussian, Sinc2, and Triangle2. We also introduced and characterized new filters based on the modification of the Blackmann filter. Our conclusion is that the Bessel filter (in infra-, self-, and mild over-deconvolution), the newly introduced BL3 filter (in self- and mild/moderate over-deconvolution), and the Gaussian filter (in moderate/strong over-deconvolution) are the most suitable filter functions to be used in FSD.