A bass line is an instrumental melody that encapsulates both rhythmic, melodic, and harmonic features and arguably contains sufficient information for accurate genre classification. In this paper a bass line based automatic music genre classification system is described. "Melodic Interval Histograms" are used as features and k-nearest neighbor classifiers are utilized and compared with SVMs on a small size standard MIDI database. Apart from standard distance metrics for k-nearest neighbor (Euclidean, symmetric KullbackLeibler, earth mover's, normalized compression distances) we propose a novel distance metric, perceptually weighted Euclidean distance (PWED). The maximum classification accuracy (84%) is obtained with knearest neighbor classifiers and the added utility of the novel metric is illustrated in our experiments.