The window method is a fast and efficient approach to fractional delay filter design. However, gain of designed filter,
differs from the ideal value which should be equal one. This effect, called gain deficit, negatively affects filter quality.
The essence of the gain deficit problem as well as method and results of gain deficit correction are stated in this article.
The influence of gain deficit correction on frequency response of the fractional delay filter and approximation error is
discussed. An algorithm for finding optimum gain deficit correction factor has been proposed and relations between correction factor and filter and window parameters are presented in the paper.