Overly concise Matlab version. If you get Dan Ellis' ispecgram [1] you can do something like:

    [x, sr] = wavread('rick.wav');
    x_mono = mean(x,2);
    X = specgram(x_mono, nfft, sr);
    Y = X >= imdilate(X, ones(mask_size), 'same');
    y = ispecgram(Y, nfft, sr);
    % wavwrite(y, sr, 'roll.wav');

params: nfft, masksize (tuple)

[1] http://github.com/tbertinmahieux/MSongsDB/blob/master/Matlab...