Abstract: A characteristic thumbprint is extracted from a data signal, the thumbprint based on statistics relating to the data signal. The data signal can be compared indirectly by matching this thumbprint against one or more reference thumbprints. The data signal may be any type of signal, including streaming digitized audio or obtained from static files. A database may contain a number of these characteristic thumbprints, and the database can be searched for a particular thumbprint.

Abstract: A database includes a repository of data segments to be searched, called standard streams. But rather than searching all possible segments of each standard stream, the database includes a set of index files that reference a number of different segments in the repository. Each index file provides information about whether various data segments in the repository are likely to match a given test stream, although in the presence of noise there may be multiple possible matches. By consulting a number of the index files, a searching algorithm identifies a set of candidate data segments to test and thus reduces the number of streams that must be tested.