1. A method of performing convolutive blind source separation, comprising: transforming each of a plurality of input signals into frequency domain; calculating values of coefficients of unmixing filters corresponding to frequency bins by performing a gradient descent process on a cost function at least dependent on the coefficients of the unmixing filters, wherein in each iteration of the gradient descent process, gradient terms for calculating the values of the same coefficient of the unmixing filters are adjusted to improve smoothness of the gradient terms across the frequency bins; with respect to each of the frequency bins, estimating source signals by filtering the transformed input signals through the respective unmixing filter configured with the calculated values of the coefficients; and transforming the estimated source signals on the respective frequency bins into time domain, wherein the cost function is adapted to evaluate decorrelation between the estimated source signals.