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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: 2) by JoeMerchant on Wednesday July 10 2019, @02:05PM (1 child)
This is a rehash of the "digital watermarking" kerfuffle back in early mp3.com days...
Some people will notice, most won't. If it bothers you, don't pay for it. Plenty of options out there today.
🌻🌻 [google.com]
(Score: 3, Interesting) by AthanasiusKircher on Wednesday July 10 2019, @04:47PM
Actually, I think this is quite different. The difference is the intention, which influences the required implementation.
Digital watermarking was mostly used for copyright ID purposes and such. Basically, a very weak audio signal (essentially inaudible) was introduced into the file. While too weak to be audible to listeners, it uniquely identified the file. And it was very difficult to remove without screwing up the actual audio, because it was effectively "noise" in the background at a very low level. The only way to mask it would be to introduce much stronger noise and then remove that noise, in the process wrecking the actual audio signal you want.
The difference in this method is that they want to introduce a signal that can be detectable when the audio is played. The digital watermarking method is easy to spot when analyzing a file on a computer, but a microphone listening to that recording broadcast in a hotel lobby likely wouldn't be able to differentiate between the watermarked file and a non-watermarked version, because the "noise" for the watermarking is so low.
TFA's method wants to make a signal in the audio that, say, your phone could pick up just by hearing the audio broadcast in a hotel lobby, yet is not perceptible as different to human ears. As I said, I think that would be easy to do with access to the individual instrument tracks before a recording is mixed. The sample recording in TFA, however, is very noticeably different.
Good watermarking technique provides very little distortion, and I know tests show very few people can notice a difference in the audio sound when you listen back-to-back. However, if you haven't, please listen to the two samples in TFA. I bet the majority of listeners could probably notice the two tracks sound "different" (unlike with watermarking). They may not be able to identify precisely what's "different," and they may not be bothered by the distortion, but I bet they can hear it, say, in a triangle test. It's not subtle at all.