Methods and appratus for characterizing media

An apparatus to create a signature representative of media, the apparatus comprising:

• a transformer to convert at least a portion of a block of audio into a frequency domain representation including a plurality of frequency components;
• a decision metric processor to:
• define a band of frequency components having real and imaginary spectral components;
• define vectors for respective frequency components, the vector for a first one of the frequency components comprising the real and imaginary spectral components for the first one of the frequency components;
• and
• determine a decision metric using linear combinations of dot products of the vectors for the frequency components;
• and
• a signature determiner to determine the signature based on a value of the decision metric.

A method, comprising:

• converting at least a portion of a block of audio into a frequency domain representation including a plurality of frequency components;
• defining a band of frequency components having real and imaginary spectral components;
• defining a plurality of frequency bins within the band;
• determining respective difference functions for each of the frequency bins using a product of the real and imaginary spectral components of a corresponding group of the frequency bins, wherein the corresponding group for a first one of the frequency bins includes at least the first one of the frequency bins and a second one of the frequency bins selected based on the first frequency bin;
• determining a decision metric by summing the difference functions;
• and
• determining a bit for a signature based on a value of the decision metric.

A tangible article of manufacture comprising machine readable instructions which, when executed, cause a machine to at least:

• convert at least a portion of a block of audio into a frequency domain representation including a plurality of frequency components;
• define a band of frequency components having real and imaginary spectral components;
• define a plurality of frequency bins within the band;
• determine respective difference functions for each of the frequency bins using a product of the real and imaginary spectral components of a corresponding group of the frequency bins, wherein the corresponding group for a first one of the frequency bins includes at least the first one of the frequency bins and a second one of the frequency bins selected based on the first frequency bin;
• determine a decision metric by summing the difference functions;
• and
• determine a bit for a signature based on a value of the decision metric.