Patent ID: 8244527

Claim:
A method of correlating a test audio signal derived from a receiver to a reference audio signal, the method comprising: converting a first block of the test audio signal to a corresponding first frequency spectrum; selecting segments between first frequency components of the first frequency spectrum as first test segments, the first test segments having first test slopes; comparing, using a processor, signs of the first test slopes to signs of first reference slopes of first reference segments derived from the reference audio signal; selecting segments between second frequency components of a second frequency spectrum as second test segments having corresponding second test slopes; comparing, using the processor, signs of the second test slopes to signs of second reference slopes of second reference segments derived from the reference audio signal; and determining a match between the test audio signal and the reference audio signal when at least a threshold ratio of the first test segments match the first reference segments and at least a threshold ratio of the second test segments match the second reference segments.