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To store the data, the two doctoral students and their colleague, Master's student Gabriel Voirol, make minimal changes to the music. In contrast to other scientists' attempts in recent years, the researchers state that their new approach allows higher data transfer rates with no audible effect on the music. "Our goal was to ensure that there was no impact on listening pleasure," Eichelberger says.
Tests the researchers have conducted show that in ideal conditions, their technique can transfer up to 400 bits per second without the average listener noticing the difference between the source music and the modified version (see also the audio sample). Given that under realistic conditions a degree of redundancy is necessary to guarantee transmission quality, the transfer rate will more likely be some 200 bits -- or around 25 letters -- per second. "In theory, it would be possible to transmit data much faster. But the higher the transfer rate, the sooner the data becomes perceptible as interfering sound, or data quality suffers," Tanner adds.
The researchers from ETH Zurich's Computer Engineering and Networks Laboratory use the dominant notes in a piece of music, overlaying each of them with two marginally deeper and two marginally higher notes that are quieter than the dominant note. They also make use of the harmonics (one or more octaves higher) of the strongest note, inserting slightly deeper and higher notes here, too. It is all these additional notes that carry the data. While a smartphone can receive and analyse this data via its built-in microphone, the human ear doesn't perceive these additional notes.
[...] To tell the decoder algorithm in the smartphone where it needs to look for data, the scientists use very high notes that the human ear can barely register: they replace the music in the frequency range 9.8-10 kHz with an acoustic data stream that carries the information on when and where across the rest of the music's frequency spectrum to find the data being transmitted.
Eichelberger M, Tanner S, Voirol G, Wattenhofer R: Imperceptible Audio Communication[pdf]. 44th IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), Brighton, 12-17 May 2019
(Score: 3, Interesting) by JoeMerchant on Wednesday July 10 2019, @11:45AM (2 children)
What's a "normal" .mp3 data rate, like 128Kbps? Side channel and you're done: 128.4Kbps. Unless we're trying to be clever and chirp the data out in the actual audio (which is what this "sounds like.") In that case this is sort of the opposite of MP3 research which tried to store only those things important to human perception of audio.
Point of curiosity, if MP3 and this really achieve their respective goals, then MP3 encoding should pretty much destroy this data stream, since it's unimportant to human perception of the audio.
I did something very similar with steganography in still images - very high data rates, imperceptible differences in the image, but I needed to use .png or other lossless encoding schemes - and the resulting compressed files did grow as you stuffed more information in them, even though you couldn't see the differences. Encoding with .jpg would completely wipe out my encoding scheme.
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(Score: 2) by Pino P on Wednesday July 10 2019, @03:25PM (1 child)
It turns out that existing ATRAC, MP3, AC-3, AAC, Vorbis, and Opus encoders do not perfectly "achieve their respective goals." This is howCinavia and other existing watermarking schemes manage to slip by the slightly imperfect psychoacoustic models in these encoders.
(Score: 2) by JoeMerchant on Wednesday July 10 2019, @03:55PM
Yeah, how long ago was all that bruhaha about watermarking on audio files? Seems like almost 20 years now.
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