A small gate array is evolved extrinsically to carry out a low pass filtering task defined over fifteen different frequencies. The circuit is evolved by assessing its response digitised sine waves. Two different fitness functions are contrasted. One is based on computing the sum of the absolute differences between the actual response and that desired, the other is defined by examining characteristics of the Discrete Fourier Transform of the output. The gate arrays possess some linear properties, which means that they are capable of filtering composite signals which have not been encountered in training. This includes signals with noise added and with frequencies which are not in the training set.