Posts Tagged ‘frequency’

It’s getting kind of hectic

Those tremors you feel in your high-rise building may not be an earthquake.  Ten minutes of violent shaking in a 39-story Seoul skyscraper were attributed in 2011 to “17 middle-aged people” doing Tae Bo to “The Power” by early 1990s German hitmakers Snap!

Every building has its own natural resonances that can be excited by rhythmic activity.  In most buildings these resonances are relatively docile and hard to excite, but when wide structural spans and thin slabs lead to a low natural frequency, it doesn’t take many kickboxers to get things…kind of hectic.

Did you hear that meteor?

This past weekend, the Perseid meteor shower reached its peak overnight between Sunday and Monday.  With a little patience and clear skies, the electromagnetic radiation in the visible spectrum that meteors release is easily seen.  But did you know that meteors also release very low frequency radio waves, below 30 kilohertz? According to livescience, going back hundreds if not thousands of years, people have claimed to hear sounds of meteors as they raced across the sky.  The very low frequency radio waves travel at the speed of light (not at the speed of sound) and arrive at the same time observers see a meteor passing overhead.  However, the radio waves need a transducer to could create a sound that is audible to people. This phenomenon is known as electrophonics, and in order to study it further, physicist Colin Keay created sounds in ordinary objects by exposing them to very low frequency radiation in a laboratory. Lightweight, membrane-like objects such as aluminum foil, foliage, thin wires, even dry frizzy hair produced sounds that were easily heard.

2012 Geminid Meteor Over Texas

Never having heard this before, we thought we would head out to Long Island to try and hear it for ourselves. We saw and heard a few things…First, there are quite a few sky-watchers in New York, which unfortunately meant that second, people noise and car stereos are louder than the sound from meteors.  Also, being by the beach, the sound of the ocean waves were also louder than the meteors.  Even if we couldn’t hear them this time, and although there were a few passing clouds, meteor showers still create a wondrous sight.  We will just have to make plans to go somewhere a bit quieter next time.


A new record

Putting a new spin on the long-playing vinyl record, an editor at Instructables has devised a new method for producing LP records using a rapid prototyping “3D printer”.  Working directly from a digital audio file, Amanda Ghassaei uses the waveform profile to create a 3D computer model of the familiar LP groove, which is then built up in physical form by a UV-cured resin printer.

Despite the cutting-edge 16-micron resolution of the printer, the end result is rather crude, with a frequency response and audio quality as yet far beneath a typical analog vinyl record.  The all-digital noise introduced by the discrete print (in time, aliasing, and in amplitude, quantization) is also harsh compared with the traditional “warm” analog distortion sought after by vinyl enthusiasts and audiophiles.  Even so, one could foresee a niche market for one-off, just-in-time pressing of records to keep alive long out-of-print material (or new material that might be in limited demand).  Even though this can be accomplished with .mp3 files or CD-R discs, sometimes there’s simply nothing like setting needle to vinyl!

[via Wired]

Drop-less droplets

In a setup that’s equal parts science and Harry Potter, scientists at Argonne National Laboratory acoustically levitate liquids in midair to further critical pharmaceutical reasearch. Using a technology originally developed by NASA to simulate microgravity conditions, the pharmaceutical droplets are suspended in midair using standing waves of inaudible ultrasound generated by small speakers above and below.

By suspending a drug this way—free from any container or other physical contact—scientists can study its various forms and the ways it might be absorbed by the body. Not to mention putting on a pretty cool show in the process!

FFFFT (the fast fast fast Fourier transform)

No, it’s not the sound of the air being let out of your tires!

Researchers at the Massachusetts Institute of Technology have just published a ground-breaking computational method for analyzing digital signals, including sounds and images.

The Fourier Transform is a way to break a complicated signal down into its most basic components, and it’s how computers manipulate things like acoustic and visual information—everything from your jpeg and mp3 files up to complicated acoustic measurement and analysis gear that consultants like ourselves use daily.

Fourier Transform

The last major improvement in the efficiency of the Fourier Transform came in the 1960s, with the advent of the “Fast” Fourier Transform (often denoted FFT).  That was a long time ago, but the FFT is still the method of choice for on-the-fly number crunching in everything from cellphones to video games to high-end audio and graphics workstations.

The new algorithm that MIT has devised (a “nearly optimal sparse Fourier transform”) is substantially faster than the FFT for a large range of realistic and useful cases—up to 10 times faster.  It isn’t hard to imagine that such a major leap in efficiency will lead to smaller, cheaper, and more powerful electronics, since the work they do under the hood just got a whole lot easier!

[via MIT News. Graphic: Christine Daniloff]

Catch a wave

You may know that the sounds you hear travel through the air as waves, but the invisibility of air makes this concept a tricky one to visualize.  For those who like physics demonstrations (and who doesn’t), we recently came across this video of a series of pendulums—and the pendulum is perhaps the most accessible form of wave motion we witness in everyday life.

A pendulum’s length determines its frequency, just as sound waves in air have a frequency that corresponds to pitch.  The demonstration superimposes different frequencies to illustrate traveling waves, standing waves, beats, and “random” noise, which are all phenomena that come from mixing different frequencies together.