Slashdot Mirror
Embedding Data Signals In White Noise
Anemophilous Coward writes "ZDNet has the following article which describes a company that 'has devised a method for sending wireless signals over ordinary audio speakers so that humans can't hear them. With this same technology, radio stations can unobtrusively transmit ads, Web site URLs, or information about music and artists to in-car cell phones.'" Here is some further reading about the company, Intrasonics.
We all know this is just a cover story for the REAL secret messages in the static!
....more invisible voices urging me to do bad things.
.
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"A microprocessor... is a terrible thing to waste." --
GeneralEmergency
Blow your mind
And life for all dog's everywhere will never be the same.
who will be the first artist to embed lyrics, trivia, etc in their CDs?
The truth doesn't care what I think.
Advertising everywhere... no escape. I remember reading a short sci-fi story about this many years ago. Unfortunately, it looks like somebody else read it as well...
The pr0n industry should be all over this. You can watch a movie at home with a special "doll", responding to commands...
Where can I buy stock?
"Give a woman two glasses of wine and some pad thai, and they'll agree to just about anything." the Sports Guy
I wonder if this technology could be modified to watermark the source of the signal?
But if they are saying that it is random pops and cracks how will converting it into MP3s affect it?
I guess also, how would extra noise because one has a lousy stereo do to the signal?
This is just like that time that the phone police were sending me those messages through the rings, man. Exactly the same, except different. Man.
Let me guess, by using the correlation of psuedo-random noise sequences summed with the signal.
-Chris
--an unbreakable toy is useful for breaking other toys--
This is an interesting idea, using psychoacoustic modeling to open a data channel in audio. The article describes some applications, and I'll certainly admit that some of them sound irritating or possibly dangerous (from a security standpoint.) Others sound better.
But not everything interesting to do with this will be done by the company involved, because it may not make good business sense or they may not have thought of it. I'd be interested in what slashdotters can think of to do with such a channel. The obvious use of embedding artist and recording information is mentioned, and I like that one a lot. It would be great to have a radio displaying those things, and to be able to scroll back and look at the last N songs. This would let you find out what that song you heard the end of was, or do a statistical analysis of a station's playlist, whatever you want.
A use that occurs to me is adding the information to advertisements so that adverisers can automate the task of making sure that they get what they pay for. Even performers could use an "ad id" check to make sure they get their voice-over royalties and the like.
Of course, voice of america and similar programs could use this right away. First they start adding this hidden content to all programming, using encrypted books, articles, or any other easily accesible source. They can then easily put a specific message with a specific key into a program that certain people can unlock. There's no entropy difference between the "real" message and the usual dummy ones to detect.
Hmmm lots of fun to be had here...
Hm, could someone send a mass-broadcast virus this way?
Trolls lurk everywhere. Mod them down.
"I can hear it, can't you?"
-dameron
Others have already observed that it's not a frequency thing, but let me expand on that.
Frequencies are already optimized for human hearing, and it's not usually possible to send, say, a 40,000Hz signal on most anything you can think of, analog or digital. Standard phones have a bandwidth of something like 3 K Hz. CDs of course top out around 20,000Hz, give or take a bit. (It's not a perfect cutoff at 22050, it's a curve, so there isn't quite a point you can say is "the limit".) I don't know for certain but I'd bet FM can't transmit those frequencies and be compliant with FCC regulations. (Of course the tech could do it in theory, but the radio station may have to leave their allocated frequencies to do it; I don't know for certain.) AM could do it in theory but based on the low quality of the signal I hypothesize that something is preventing high frequencies from getting through.
Finally, the coup de grace is that our speakers are optimized for human hearing, pretty much no matter what. Covering the bases from 20Hz - 20,000Hz is a hard enough problem without pushing the required range up another couple of octaves.
In fact, what the company is proposing seems to be in some sense the inverse of MP3 coding. MP3 coding strips the signal of things that you can't hear through by analysing what is psychoacoustically masked in the original signal. The MP3 encoding process can then focus on just the parts of the signal you do hear, which is obviously going to require less space, except in some pathological cases where the whole sound is perceivable (like a pure sine wave tone).
From what I understand of the marketing, the part of the signal that an MP3 encoder strips out is exactly where they would place their data. They can stick any data they want in there and we just plain won't hear it, but a computer+microphone doesn't have this problem.
Interesting corrolary: The time frame this will work in is limited, as digital transmission usually uses compressed audio, and the act of compressing the audio will preferentially eliminate this data. (Or does digital radio transmit an uncompressed stream?) They'd better get marketing this now, so that there's an installed base and they can try to later create receivers that will re-add their signal on the receiving side. Of course, if all anybody is using this for is advertising, I can't imagine we're going to go out of our way to buy "Advertising Enabled!" digital radio receivers.
"Can you hear me now? No? Good!"
Good judgment comes from experience.
Experience comes from bad judgment.
One of the things that came with the cuecat kit was a rca cable that was meant to go from your computer to your sound card. Apparently, while watching TV they'd embed a signal into the audio that the cuecat software would pick up, and it would take you to their site.
Since one of our local channels was owned by the Belo corp (who owned a LOT of Digital Convergence stock), they pushed it HEAVILY, and embedded URLs in the news program.
So, nothing new.
"Sometimes a woman is a kind of religion, she can save your soul & set you free from all your sins" - Bad Examples
In europe, there exists a similar technology called RDS for "Radio Data System". It's on the air for about 10 years now and allows for these cool features since then:
- Show the Station name in your radio display
- Show what's playing
- Certain stations are transmitted over several frequencies. RDS knows the alternative frequencies of your stations and automatically switches to the best frequency
Check out the Portable People Meter from Arbitron. It can recognize subaudible watermarks in music including over radio, Musak, and even some streaming audio compressions. Arbitron uses it for ratings purposes.
Of course, then there is IBOC from Ibiquity which is an on-channel digital enhacement for AM and FM signals, part of which could be used for datacasting, as part of most DTV signals will.
22050 is an absolute upper cutoff in the encoding system, and in theory you could encode a 22,049 Hz signal into Red Book audio. I said it's not a perfect cutoff because it's impossible to build an audio filter to cut off precisely at 22050 Hz, which is beyond the scope of a Slashdot comment; please consult a signal processing resource on how signal filtering works.
;-) I just like to be precise when possible, and prefer practical realities to theoretical ones, which is why I'm in Engineering college.
At the recorder, you must cutoff signals over 22050 or risk the horrible problem of aliasing (again, out of scope of a Slashdot post but pretty interesting). Since you can't have a perfect cutoff filter, you generally can't record 22049Hz signals except with extreme attenuation (in the specific case of 22049, it will well below the noise floor). Generally, when the CD players re-construct the sound, they will also do some filtering as a side-effect of how they do it. So you can't generally play back a 22049Hz signal either, even if you directly encode it onto a CD.
So while you can encode it, you can't record it directly and you can't play it back, so in a very real practical sense, 22049Hz is not usable with CDs. And so on and so forth for the other frequencies between 20000 and 22050. It's a smooth curve (and not necessarily the same one for two pieces of equipment, though my impression is that they have standardized somewhat because it's cheaper that way), so in a real-world CD recording and playback application, in a very real way there's no particular cutoff frequency you can directly point at, even though there's one in theory.
In general, it's a pretty pedantic point.
This, by the way, is part of the reason that CD's sample at 44100, instead of 40000. 40000 would be somewhat more efficient with the storage medium, but you'd have problems with the fact that you have no room to filter out the higher frequencies without hitting "good" ones as well. There are other concerns too, that's not the whole story, but it is a very significant part of it. In fact that goes for this whole post; I'm skimming over a lot because this is only a Slashdot post. (Like "20-20,000 is only a convenient fiction", the exact way filters behave, etc.)
This is Push technology, so you could do any kind of push you do with channels now you can do with this. Here a couple of idea's I had:
Song Titles - How about ID tags so you can actually see the exact title of the song your listening to? You can keep a 10 song list like caller ID. You can see the last few songs you listened to. For advertisers you would keep one text line scrolling on the display.
Second Audio Channel - A secondary program at AM quality on an FM station. Kinda like how HDTV can have up to 6 lower quality channels.
Radio for the Death - Close Captioning of radio lyrics. 'Nuff said.
Emergency Broadcast Technolgy - Give both a readable text warning and GPS cordinates of pending danger.
Exact Station Date and Time - Isn't that what you really want half the time you turn on the radio anyway.
Weather and News Broadcasts - Get the local or national news in an instant.
Automatic Request line # - Never have to listen for those damn # to call while your driving.
Possible interactivity - Broadcast a survey to a cellphone, you log your answers, and then you transmit your results.
You say things that offend me and I can deal with it. Can you?
I have always liked when I put a CD into my player and the name of the song and the artist comes up on the LCD screen. Wouldn't the use of the "White noise effect" allow radio stations to transmit this information to radios for the same display purpose?
*song is ending* "Damn, I love that song, I wish I could remember who sings it. Maybe the DJ will say the song title before the next song comes on." Oh wait, DJ's don't do that anymore...Just show it to me on the LCD!
-Krnl
http://krnlpanic.com