How low can you go? Ghosts & where sound becomes vision?

[imagist]

I came across this about elephants infrasonic communication and found it interesting - I wonder what mics/equipment the researchers are using?

BBC News - Elephant 'secret language' clues

apparently we cannot hear below about 20hz and wikipedia defines infrasonics as 20hz to 0.0001Hz

"20 Hz is considered the normal low frequency limit of human hearing. When pure sine waves are reproduced under ideal conditions and at very high volume, a human listener will be able to identify tones as low as 12 Hz. Below 10 Hz it is possible to perceive the single cycles of the sound, along with a sensation of pressure at the eardrums."

I also found this interesting -

Infrasound has been known to cause feelings of awe or fear in humans.Since it is not consciously perceived, it can make people feel vaguely that supernatural events are taking place.Some film soundtracks make use of infrasound to produce unease or disorientation in the audience. Irréversible is one such movie.

and -

The Ghost in the Machine Research by Vic Tandy, a lecturer at Coventry University, suggested that the frequency 19 Hz was responsible for many ghost sightings. He was working late one night alone in a supposedly haunted laboratory at Warwick, when he felt very anxious and could detect a grey blob out of the corner of his eye. When he turned to face it, there was nothing.The following day, he was working on his fencing foil, with the handle held in a vice. Although there was nothing touching it, the blade started to vibrate wildly. Further investigation led him to discover that the extraction fan was emitting a frequency of 18.98 Hz, very close to the resonant frequency of the eye (given as 18 Hz in NASA Technical Report 19770013810). This was why he saw a ghostly figure — it was an optical illusion caused by his eyeballs resonating. The room was exactly half a wavelength in length, and the desk was in the centre, thus causing a standing wave which was detected by the foil.

Tandy investigated this phenomenon further and wrote a paper entitled The Ghost in the Machine. He carried out a number of investigations at various sites believed to be haunted, including the basement of the Tourist Information Bureau next to Coventry Cathedral and Edinburgh Castle.

[chrisnewton]

In my spare time I occasionally play the tuba. One day while practising at home in my living room, I noticed out of the corner of my eye that my TV set (CRT) would strobe occasionally (black horizontal scan lines rolling up the screen). When I stopped playing the strobing stopped. Figured out that it only happened when I hit a certain low note. Don't remember which pitch, maybe a low C. I've tried since but haven't been able to reproduce the phenom. Maybe my tuning was just off enough to not trigger my eyeball oscillation. Harmonic of scan rate? I'm relieved that it wasn't just another acid flashback.

Chris Newton

[Izen Ears]

  This is awesome!!  Thanks for the cool video.  Thanks Imagist whatever your name is.  I too wonder what the hell kind of mic or device can hear that low?

  Dan Izen

[Marc Wielage]

In my spare time I occasionally play the tuba. One day while practising at home in my living room, I noticed out of the corner of my eye that my TV set (CRT) would strobe occasionally (black horizontal scan lines rolling up the screen). When I stopped playing the strobing stopped.

We call that "chewing flicker" in the world of video. My guess is that it's some kind of resonant frequency that happens to interact with our eyes in such a way as to cause a flicker/strobe issue with certain kinds of monitors. I thought for years that it was actually causing the monitor to react, and it took me awhile to figure out that it was just my own eyes.

I wouldn't be surprised if this 18Hz figure (and related harmonics) is some magic number that causes weird reactions in humans. "Weird vibrations."

--Marc W.

[Bondelev]

http://en.wikipedia.org/wiki/Brown_note

[curleysound]

I don't know about low frequencies, but I was at a Joan Jett concert years ago, and when she hit high notes, I saw double, and got dizzy. It was the strangest thing!

[Guest Ken Mantlo]

I don't know about low frequencies, but I was at a Joan Jett concert years ago, and when she hit high notes, I saw double, and got dizzy. It was the strangest thing!

Bad dope is a M----r F----r!

[curleysound]

Nope, nothing like that was involved. I was straight as an arrow.

[studiomprd]

"  I was straight as an arrow. "

it is not about the arrows, it is about the archer!

[curleysound]

I wasn't an archer at that time either

[studiomprd]

a number of years back, I read an astronemy article that indicated that stars were making what is, by definition, 'sound'; the frequencies are measured in cycles per year, or decade...

[David Waelder]

stars were making what is, by definition, 'sound'; the frequencies are measured in cycles per year, or decade...

If I understand the matter correctly - not at all a foregone conclusion - light is really just sound at a very high frequency. That is, it's all the same and the distinction between them comes from the rate of the vibration.

David

[Derek H]

I've actually done a small amount of homework on this topic a few times.. 

Last year I worked on a "paranormal" ghost hunting type show where they would make audio recordings in a "haunted" place and then play them back at different speeds and "hear things" that weren't heard in real time..

I was highly suspicious of the recording equipment quality..  even the great mics we use like Sennheisers and Schoeps aren't generally designed to be responsive to frequencies we can't hear.  Though Schoeps does offer a cmc model with an extended frequency response if I remember right.

To record sound that low you need a special mic that is sensitive to lower than audible freqs..  Earthworks makes some that go down pretty low.  I'm sure there are others that are designed for scientific purposes.

The other gotcha that I never really followed up on was remembering that most A/D converters have filters built into their design that cuts out infra and ultrasonic "noise".  ..Somebody fact check me on that one..

So I think it's more than a matter of choosing the right mic.  I also thought about if recording in analog might be a better way to record infrasonics.. 

I never had the chance to test anything tho.. 

As far as other animals that use infrasonic sound check out Mr. Hippopotamus who has some special underwater hearing faculties.  Similar to whales it allows him to judge the distance of other hippos miles away via the time delay between hippo calls heard simultaneously through the air (ears above water) and below water (inducted through ear and jaw bones beneath the surface).  ..Also needs fact checking but I've read studies on this.

I've also heard that migratory birds use infrasonic sound to aid in navigating.  Something to do with having hollow bones.. more than just light-weight they also apparently resonate with some infrasonic frequencies that are associated with large landmarks like mountains..

Obviosuly I'm not an expert but I always thought it was pretty cool stuff!!   

[Matt McGowin]

interesting