An apparatus for determining a similarity information on the basis of one or more input signals is configured to determine a zero crossing information describing a number of zero crossings in a respective portion for a plurality of portions of at least one of the one or more input signals. The apparatus is configured to perform a comparison on the basis of the zero crossing information, in order to determine the similarity information. A method for determining a similarity information and a computer program are also described. Moreover, an apparatus for determining an autocorrelation information and an apparatus for determining a cross-correlation information are based on similar considerations.