A method for measuring bi-directional similarity between a first signal of a first size and a second signal of a second size includes matching at least some patches of the first signal with patches of the second signal for data completeness, matching at least some patches of the second signal with patches of the first signal for data coherence, calculating the bi-directional similarity measure as a function of the matched patches for coherence and the matched patches for completeness and indicating the similarity between the first signal and the second signal. Another method generates a second signal from a first signal where the second signal is different than the first signal by at least one parameter. The method includes attempting to maximize a bi-directional similarity measure between the second signal and the first signal.