I have a very low voice and enjoy singing or humming along with the bass line in music some times. While I was singing along with a song, all of a sudden my monitor started to go a bit nuts and wave. When I stopped singing (or changed notes) it stopped.
I turned to my roommate, "Can you see that?"
"Nope."
It turned out that if I sang a note at the same frequency as my monitor's refresh rate, the image on the screen would start to modulate up and down in a wavy sort of way. But to my eyes alone. Must have been something with the motion of my eyes or my head matching the refreshing of the screen.
I think that's exactly right. Try chewing crackers or chips (the crunchier the better) while looking at an LED clock (like a microwave). Most work, depends on refresh rate. There's a good chance you'll see the same sort of waviness.
Many times at notting hill carnival I have stood in front of a 20 foot tall wall of speakers and had my vision go blurry due to the 30Hz bass tone at 125db making my eyeballs oscillate in my skull.
You head is a resonating structure. If you make it resonate at a frequency that has an interesting relationship to your monitor it will shake your eyes (being part of your head) so that you can see the refresh. (Or at least that's my theory.)
I used to pulse dial a phone using the hook switch to get free calls. There was a phone in the bar in my college that only accepted incoming calls. It did this by having no dial. Of course, that didn't stop you from tapping out the phone number if you could get the beat right.
The other stupid phone that I hacked around was a pay phone in a flat that I rented where you'd pick up the handset and get a dial tone but the keypad was inoperative unless you put in money. Hello DTMF pocket dialer.
It's not unreasonable to think that someone could emulate the carrier tone with their voice. After all the modem had to work inside the frequency range used for voice communications.
The tones used in DTMF were chosen to minimize accidental talk-off. They're relatively widely separated, with no harmonic relationship between any given pair.
When I was a kid, I'd load executables into a text editor or hex editor to see what was inside. I quickly figured out how to identify uncompressed graphics and audio data by sight, and to identify various opcodes by their ASCII interpretation. It made ripping and patching a lot quicker since I could eyeball it first before deep diving, and made it trivial to find encrypted portions in the executable.
I still do it sometimes.
Another, less useful skill (now) was the ability to detect a failing floppy disk by resting my hand on top of the drive while it was reading. I also resurrected a couple of seized hard drives by opening the case and spinning up the platter with my finger, much to the shock and dismay of onlookers.
When I was a kid, I'd load executables into a text editor or hex editor to see what was inside.
So did I. I got stuck on a text adventure that came on a magazine's cover disk so I cracked open the executable to see what verbs I could use.
It had lots of swear words it could detect (which I recognized) including "c--t" (which I didn't recognize). In a matter of fact way I asked my parents, "What does c--t mean?" I seem to recall the magazine sending us a free copy of Wing Commander shortly thereafter ;-)
You just need to get the drive spinning. The motor will set it to a constant speed, but when the drive has seized, it can't start the platter spinning to begin with.
However, once you open the drive, you have VERY limited time to copy the data off since it's designed to run in clean room conditions (internally).
I could hear the extremely high-pitched capacitor singing in many CRTs, allowing me to determine before I walked in a room if there was a TV or computer monitor on.
It was awesome. Felt like my very own mutant power.
I think a lot of children can do this. I remember in middle school the entire class complaining that the TV was on, with a blank screen, and the teacher having no idea how we knew.
I can still tell when my printer has been left on, though I haven't been a child for a long time. It's actually quite an irritating sound, hence why I leave my printer off most of the time :-P
It has to do with how hearing degrades as a person ages. Some places use this to their advantage and install devices that emit high pitches so as to stop teenagers from loitering there. I know the Ikea in Brooklyn has it, for example.
Me too. I went over to see a friend who had an entertainment center with doors that closed over the TV. I walked in and immediately asked if his TV was on. He said it wasn't (the doors were closed and no sound was coming from the speakers). I insisted that it was. To his surprise, it was. They were amazed. I was in my mid-20s.
I still do the same for almost all CRTs. I'm pretty young though. The most annoying was waiting for the ACT to start while hearing a loud super high-pitch electronic whine went on every five seconds.
When I was a kid, I took apart an old VHS deck. One of the huge ones, from when they first came out. Not sure what I thought I was doing, but I proceeded to attach the output of the transformer into the transmitting portion of an old rotary phone I had also disassembled. Our phone line went dead. According to our neighbors, our subdivision's entire phone network went down too. Not sure if that's true or not, but I am definitely surprised I didn't burn down the house that day.
If I am not mistaken this was the essence of the (fictional) 'blotto box'. The recipe entailed hooking a power generator into a phone trunk line and taking out the majority of a subdivisions phone circuits. I was written up in many of the phreaker/anarchy text mags that were popular at the time, but I never heard of anyone actually trying it. I'm also pretty sure the authors were not aware of things like fuses...
Order a pizza from the campus online computer, crash computer, call inquiring about the status of said pizza, receive many apologies and a free pizza. Not proud of it anymore though.
I used to be able to tell which of the long row of Model 33 TTY's was left on at the college computer center by whistling the 300 baud carrier and modulating it a little. The ones that were on would start typing gibberish.
A friend would call with his computer out of the blue. I'd hear the tone, and whistle the matching tone back to keep it happy until I could get my own computer up and running to link up.
Back in my phreaking days, I was grounded so often that out of sheer boredom I learned to whistle DTMF tones. I could dial a number simply by whistling it.
You're thinking in the frequency domain, which is natural. Try to think, instead, of what a dual-sideband suppressed-carrier signal looks like in the time domain. It looks for all the world like a single frequency with rapid variations in amplitude (which can be accomplished by bubbling the air through a carefully-controlled reservoir of saliva). If you can mimic the time-domain signal, you can mimic the frequency-domain signal, since they're just two ways of looking at the same thing.
I tried to find a friend to train with me so we could do DTMF, or rather CCITT #5.
I could whistle the 2400hz and 2600hz reasonably well (not at the same time) which allowed me to hang up on international calls if I wanted to.
Oh, I was also pretty adept at war-dialing manually in the dark. Dialing numbers in sequence, but then switched the light on and wrote down the details if I found a modem or a controllable voice mail or pbx system.
I don't know about whistling, but tone mis-detections were fairly common in the early days with some folks' voices, and they still arise in a few of the systems.
We tried to reduce this mis-detection within the hardware and software of a voice response system back in the early 1990s. This commonly involved intentionally requiring longer tone input detection before the tone action was triggered, but it was left programmable for the end-users.
I know someone that still triggering a tone detection in a conferencing system within the last few years; she'd end up muting herself in the call, which lead to appreciable frustration.
If you look at the standard 3x4 phone number grid, each row or column had a specific frequency assigned to it. A single button would play both the row and column tones simultaneously.
edit: I just remembered, it's actually 4x4. There is a fourth column labelled ABCD. Forget what it's used for. I was mostly a theoretical phreak :)
The 6 extra keys (*, #, A, B, C, and D) where meant to be used for remote control of devices attached to the telephone network. They were heavily used for test equipment. Another use was in the old Army AUTOVON system where the letters were mapped to call precedence levels.
You can't generate DTMF tones with throat singing. I do some throat singing, and a better name for it is overtone singing. You're not producing two different fundamental tones as DTMF would require, you're producing one fundamental tone and then emphasizing and suppressing various harmonics (overtones).
I also used to run a BBS. We had a small enough userbase (a couple hundred folks, with maybe 30-40 real diehards) and modem tones were unique enough above 14.4K that I could tell with reasonable certainty whom was calling in at any given time. I don't know if this would scale but it was pretty handy for freaking out anyone who happened to be hanging out in the computer room.
Also, at no point did I abuse my local console access powers to cause people to fly into heavily fortified sectors in Trade Wars. That would be mean.
"I used to be able to tell whether a CRT monitor or TV was on or off being in a different room. I guess I could hear the 50Hz?"
I am able to do this as well and usually attribute that to the fact that I grew up in a household without a TV. I could enter a house and immediately tell whether someone watched TV in the basement. Now, the question I have that I never got around asking:
Is this due to most people just not being able to hear those frequencies or just the fact that this sound is so common that most people just don't notice it anymore?
I could too but dont think I can anymore as have got older, though hard to find a crt to check. Suspect a lot of people just could never hear that high.
I grew up with TVs and still can hear most of the CRT sets. It's because, IIRC, the horizontal sync frequency is around 15KHz which is higher than what most people hear. The sound gets significantly louder when the TV loses signal. The same happens with NTSC/PAL frequency computer monitors (I restore and collect vintage computers, so I have a healthy collection of those).
Oddly, some higher resolution screens (XGA and above) also emit a high pitch noise. Unless there is some frequency multiplication going on, they shouldn't.
I've done this, too. Only I would whistle. Start low and gradually rise. Eventually I'd hit the right frequency.
The application was when I answered the phone and heard nothing. Sometimes it was a spurious call from a modem. Maybe a wrong number. Maybe a friend thinking I'd be available for a chat (houses usually had just one phone line back then).
BTW, I'm not sure I quite believe the story from the post. If my memory serves me correctly, it is the answering modem that would produce a tone first.
I was younger and my voice hadn't changed so it wasn't so much of a scream, more of a loud "Eeeeeeeeee...". Though I doubt it was any less annoying to the adults around.
I can make a fairly accurate guess of what type of scan an MRI scanner is running by the noise it makes. T2, PDFS, T1, types of gradient echoes etc.
I'm not alone in this and know a fair few people who can. I have managed to tell when a scan is badly set up with this technique too, really surprises people!
I could - and still can - make a pretty damn good estimation of a CRT monitor's refresh rate. I can distinguish between 60Hz, 80Hz and 100Hz with reasonable accuracy (in steps of about 20Hz). Also, anything below 80Hz gives me terrible headaches.
I spent hours as a young phone phreak trying to sieze an international (phone) trunk by whistling 2600hz like cap'n crunch did to sieze 800 trunks in the US and get free phone calls. It never worked because to sieze an international CCITT5 trunk you'd use a combo of 2400/2600hz. But I did it anyway when I was bored and tried to modulate a bit of 2400hz in there - figured one day I'd get lucky.
In the early 90's I used an old VCR tuner (over the air) to listen to telephone conversations people were making. I lived in an extremely rural area and had few neighbors.
I did something similar to this. I found that if I held down the talk button on a walkie-talkie and crossed its antenna with that of a portable TV, I was able to tune into analog cellular calls. I would adjust the frequency on the (analog, nondiscrete) TV tuner to listen to different calls.
I turned to my roommate, "Can you see that?"
"Nope."
It turned out that if I sang a note at the same frequency as my monitor's refresh rate, the image on the screen would start to modulate up and down in a wavy sort of way. But to my eyes alone. Must have been something with the motion of my eyes or my head matching the refreshing of the screen.