Alexa Scientists Claim Audio Watermarking Technique Nearing 100% Accuracy

georgecarlyle76 brought our attention to Amazon's claim of an algorithm that 'solves the 'second-screen problem' in real-time.'
'Ever hear (no pun intended) of audio watermarking?' asks VentureBeat.
It's the process of adding distinctive sound patterns identifiable to PCs, and it's a major way web video hosts, set-top boxes, and media players spot copyrighted tracks. But watermarking schemes aren't particularly reliable in noisy environments, like when the audio in question is broadcasted over a loudspeaker. The resulting noise and interference -- referred to in academic literature as the 'second-screen' problem -- severely distorts watermarks, and introduces delays that detectors often struggle to reconcile. Researchers at Amazon, though, believe they've pioneered a novel workaround, which they describe in a paper newly published on the preprint server Arxiv ('Audio Watermarking over the Air with Modulated Self-Correlation') and an accompanying blog post. The team claims their method -- which they'll detail at the International Conference on Acoustics, Speech, and Signal Processing in May -- can detect watermarks added to about two seconds of audio with 'almost perfect accuracy,' even when the distance between the speaker and detector is greater than 20 feet...
So how's it work? As Tai explains, the model employs a 'spread-spectrum' technique in which watermark energy is spread across time and frequency, rendering it inaudible to human ears while robustifying it against postprocessing (like compression). And it generates watermarks from noise blocks of a fixed duration, each of which introduces its own distinct pattern to selected frequency components in the host audio signal. Conventional detectors would compare the resulting sequence of noise blocks -- the decoding key -- with a reference copy. But Tai and colleagues take a different approach: Their algorithm embeds the noise pattern in the audio signal multiple times and compares it to itself. Because said signal passes through the same acoustic environment, Tai explains, instances of the pattern are distorted in similar ways, enabling them to be compared directly. 'The detector takes advantage of the distortion due to the acoustic channel, rather than combatting it,' he added.

'Audio content that Alexa plays -- music, audiobooks, podcasts, radio broadcasts, movies -- could be watermarked on the fly,' explains Amazon's blog post. It argues that this could be useful 'so that Alexa-enabled devices can better gauge room reverberation and filter out echoes.'

Read more of this story at Slashdot.