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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.
I want an in depth analysis of the Beatles' White Album immediately! Charles Manson was right!
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...
Using a seemingly innocuous message as a carrier wave for a truly useful message you don't want other people to know about is an old-news crypto technique, of course. But here's a fun, new place to apply it.
And you don't even need to seem to be doing anything funny during decoding (the message would obviously have to be enciphered; pass it in the clear and anyone who owns a cell tower between the two points can read it); build that into the phone/PDA. With the ridiculous proliferation of the damn things, no one will blink if you receive a call, chat for a few minutes, and then tap a few buttons. For all they know, you're sending an SMS, even if you are entering your passphrase.
All it really takes to do 3DES or Blowfish in software in a reasonable period of time is a StrongARM or similar (my Newton's got one, you cell phone must), though you'd get far better performance doing it in hardware. (Watch out for escrow, though!)
Do you have a
Ignore the messages embedded in this whitenoise.
You will Loooooooove Microsoft
You will Haaaaaaaate Open Source
Linux is eeeeeeeevil
War on Iraq is goooooooood
"As far as I'm concerned, I prefer silent vice to ostentatious virtue." ~A. Einstein
Hm, could someone send a mass-broadcast virus this way?
Trolls lurk everywhere. Mod them down.
I find it sad that everytime a new technology such as this is developed, the first instinct of the marketing people tasked with selling it is to figure out a way to make it push ads into my perceptual environment, almost guaranteeing an initial cynical reaction..
"I can hear it, can't you?"
-dameron
The Radio Data System has been around for ages and it allows precisely that: transmitting extra information with normal radio signals... Because it works by putting digital signal into inaudibile frequency, it should do exactly the same, as long as speakers have any response at 20-40Khz.
"With this same technology, radio stations can unobtrusively transmit ads, Web site URLs, or information about music and artists..
Humans tend to filter out what they don't want to hear, especially the pop, fizz and hum of white noise."
So if I understand this correctly, the technology can transmit advertisements, spam, and pop music completely unheard by the human ear by disgusing them as advertisements, spam, and pop music?
Shameless plug for my photos on Flickr
isn't white noise like britany spears, nsync, backstreet boys,etc?
oh wait...you mean the OTHER white noise
nbfn
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.
A hot new startup in California has announced a technology for encoding color information in black-and-white television broadcasts. The extra signal is encoded such that black-and-white receivers don't notice it, using a proprietary technique referred to as a ``subcarrier''. Millions of Slashdot kiddies are smitten with awe.
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
Embedding signals leads to noise with cumulants different from zero for different times, and thus the noise is not white anymore, it becomes colored.
Your display probably isn't true white either; it's made of tiny red, green, and blue dots. This article is about perceptually hiding information in audio that humans hear as "white" but that machines can pick apart. It's steganography.
Will I retire or break 10K?
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
It seems like they're using psychoacoustic masking -- which really isn't a bad idea, as it won't change the perceptual SNR (unlike the spread-spectrum white noise espoused here). Psychoacoustic masking carefully removes bits of audio information that we would be unlikely to hear anyway. Dolby Digital gets about a maximum compression about 16:1, which would do for cheap-o speakers, but it would probably be placed more around 5:1 so those with nice stereos wouldn't hear the difference. MP3 uses similar masking compression ideas, and a 128k mono bitstream gets a compression of about 5.5:1.
Let's assume some rockin' speakers with a 22kHz rolloff, and a great FM reception with 96dB Signal-to-Noise (and a very quiet listening room). That's approximately 16 bits at 44kHz or 704Kb/s of information. That has to carry both the audio and the data signal. The data signal would have to be mono, since most toys & cell phones don't have two ears (err, microphones). Now, you have a 704Kb/s bandwidth in which you only need about 1/5 = 140Kb/sec for good audio, leaving you with a theoretical maximum of 563Kb/s left for data. Put in some forward error correction and packet and coding and other overhead and you'll probably get something more akin to 200Kb/s.
But wait! Let's assume a car with some poor tweeters with a 15kHz rolloff, and poor FM reception with 65dB Signal-to-Noise with road noise added in. That's approximately 11 bits at 7.5kHz or 82Kb/s of total information. Ooops! You've exceeded your channel capacity by almost 2x, and you'll pretty much get a big fat zero data bits.
So, the makers have make a tradeoff ->
1) Low data rates: significantly less than ~200kB/sec to accomodate cheap stereos but retain audio quality.
2) Poor audio quality: significantly less than ~140kB/sec to accomodate higher data rates or cheap stereos.
3) Lose functionality on cheap stereos: but retain both good data rates and quality audio for those who can receive it.
My guess is that they'll just go to something tiny like 500b/s, in order to reach the most market share. Even at that rate, a text ad would come through right quick.
I can just see the next Furby craze, now they get instructions (programming??) from the TV!
Anyone know the max bandwith and SNR of NTSC audio?
-- Heisenberg might have slept here.
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.
This technology could encode bits in it that tell recording devices they can't record. I know what you're thinking: use old technology. But what if you record this and then all the new cd players detect this flag? Any other thoughts on this?
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