13 Jan 2008
There is also reference to a patent disclosing an audio watermarking scheme dubbed 'El Dorado' assigned to Microsoft. Inventors: D. Kirovski & H. Malvar. "What is claimed is: 1. A method for encoding values within a digital audio signal, the method comprising: receiving the digital audio signal having frequency magnitude components; analyzing the relative energy levels of the frequency magnitude components of the signal; determining whether the signal has a large discrepancy in the relative energy levels of the frequency magnitude components, wherein the large discrepancy is a discrepancy of a factor of three or more; encoding at least one bit of the digital watermark into the digital signal based on the determination."