Friday, January 20, 2012

Why Waves Are Sometimes Better Than Lines

I've talked before about the palpable experience of listening to vinyl records, but I have to bring it up again.

I was recently gifted One Small Step, a narrative of Apollo 11 featuring rocketry pioneer Dr. Wernher von Braun and renowned newscaster Chet Huntley.  I just listened to the engines roaring during takeoff and the radio communication during landing and feel distinctly more connected to these moments than I ever have before...because I listened to it on vinyl.

I grew up with ones and zeros.  It doesn't take much to copy them — ctrl+c, ctrl+v is almost metaphorical (sometimes it fully is).  While listening to Apollo 11 take off, I glanced at my turntable and saw the playhead bobbing up and down.  The needle twitched imperceptibly in response to bumps in a spiral.  These bumps were pressed into vinyl by a stamper, created from a master, which was directly dubbed from tape.  The tape, while likely a copy, collected a representation of sound by responding to electrical current supplied by a microphone, in which a tiny structure responded to changes in air pressure caused by the very engines of Apollo 11.  Again converted to electrical current, this information caused the diaphragm of my speakers to pulse in a remarkably similar fashion to the molecules of air surrounding that rocket.

Digital sampling breaks apart the waves of auditory information into a series of lines, and it is my awareness of that detail that so affects my experience.  Over 50 years later, I am witness to a purely material propagation of waves that initiated at Kennedy Space Center, and I feel connected.

Monday, January 2, 2012

Ear Canal Resonance Follow-Up

In my previous post about ugly sounds, I made a note about what I thought to be missing information regarding Reuter and Oehler's research:
I lament that there doesn't seem to be a complete, published paper by Reuter et al., at least not yet (but I couldn't wait any longer). I have no way to draw further information from their raw data or even determine how they decided what frequency range qualified as that which the ear is most sensitive to — I assumed they cited some other work, but in my search of all of their cited work, nothing seems to present such research. They presented their work in a 15 minute session at a meeting of the Acoustical Society of America in San Diego on November third.
I emailed Dr. Reuter and he responded promptly with a succinct reminder of my musical acoustics education (edited for clarity):
From a mechanical perspective the outer ear canal works like a tube, which is open at the one end (pinna) and closed at the other end (eardrum). Tubes like this can also be found in musical instruments like organs (the so-called "gedackt" register) and clarinets. One of the main characteristics of these tubes is that their transmission is especially strong at 1/4 wavelength. If you think about the speed of sound (340 m/s) and the length of our ear canal (about 27 mm), then you can calculate the ear canal resonance frequency with the equation f = c/lamba (frequency = speed of sound / wavelength): x = 340m/s / 0,027 m *4 = 3148 Hz as resonance peak.
(Note that the wavelength used is 4 times the given ear canal length, hence the multiplier.)

He even included page-specific citations for this and for some further psychoacoustic research.  While it seems like this is a fairly well-established fact, I still hope he cites the experiments that confirm the range of resonance peaking discussed.

In other news (edited for clarity):
Michael Oehler and I are carrying out further experiments about chalkboard sounds.... The whole study will be published in the middle of the coming year I suppose.
Don't let me forget to look for that.  Also, I could write about how tube-like instruments produce their sound if that part of Reuter's email made you wonder — if you're interested, let me know in the comments.