1. A method for processing an input signal represented as a graph, comprising the steps of: selecting a training data set, wherein the training data set includes pairs of signals, wherein each pair includes an unenhanced signal and a corresponding enhanced signal; determining a graph spectral transform as an orthogonal set of eigenvectors based on the graph; estimating, in a graph spectral domain, parameters of a graph filter based on the training data set; deriving the graph filter based on the graph spectral transform and the graph filter parameters; and processing the input signal using the graph filter to produce an output signal, wherein the steps are performed in a processor.