1. A method of digital watermark processing, the method comprising: receiving an audio signal; with one or more processors: performing a watermark decoding on the audio signal to extract, from the audio signal, a first electronic payload signal embedded in a preexisting watermark layer in the audio signal with a first pseudorandom mapping to time-frequency locations in the audio signal, the first electronic payload signal providing a reference to first metadata; from the watermark decoding, determining a watermark state of the audio signal; evaluating a watermarking rule based on the watermark state to determine new watermark encoding to apply to the audio signal to comply with the watermarking rule; and performing the new watermark encoding on the audio signal to embed a new watermark layer into the audio signal, the new watermark layer comprising a second electronic payload signal encoded with a second pseudorandom mapping to time-frequency locations; wherein the new watermark layer references the first metadata and second metadata, the second metadata being referenced by the second electronic payload signal.