The subject matter described in this specification can be embodied in a method that includes partitioning a received signal into a sequence of two or more segments. For a given segment in the sequence, the method includes calculating a set of frequency domain coefficients corresponding to the given segment, and identifying local peaks in the set of frequency domain coefficients by applying a threshold. The method also includes providing a multi-dimensional histogram from a plurality of peaks identified from multiple segments, wherein the multi-dimensional histogram jointly represents frequencies and coefficient values corresponding to each of the plurality of identified peaks.