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.

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.

Music (sort of) and the Brain: On Fingernails and Chalkboards

If you're anything like me, the mere act of reading the words "fingernails" and "chalkboard" in the same sentence makes you cringe.  Personally, I find the most detestable sound to be that of squeaky styrofoam.

My nightmares consist entirely of 11-16.
(Table from Halpern et al.)

I applaud those brave scientists who venture to study such horrific sounds.  Back in 1986, Halpern et al. (PDF) conducted research regarding what aspects of awful sounds contribute most to our aversions. 20 years later, Randolph Blake of that et al. was awarded an Ig Nobel Prize (interview) by The Society For Improbable Research for their work.  Evidently, this recognition in 2006 of research that "first makes people laugh, then makes them think," inspired a wave of further ugly-sound studies.  In 2008, Kumar et al. (abstract) "addressed the question of what aspects of the auditory representation of such sounds are associated with judgments of unpleasantness," and Cox (abstract) seemed to negate a small part of Halpern and Blake's work while reaffirming some other parts.  Within the past month, Reuter et al. (abstract) landed an interview on NPR to talk about their recently presented work on the subject.

I'll spare you the squeaky styrofoam and other sounds because I'm such a nice guy, but listen to this:

Classically torturous.  But what is it about that sound that makes it hurt our ears so?  You should reason that the frequencies that make up this sound must play a major part, and you might reason that psychology and physiology could play roles, as well.  Let's begin with frequency, since it's most easily tested.  Since people generally describe very highly pitched sounds as more irritating than sounds in a speaking or singing range, a reasonable hypothesis would be that if one removed high frequencies from this sound, it would sound better...well, less awful.

Better, yes.  Best? Maybe.  Let's try the opposite and remove the low frequencies.

Ouch.  What about middle frequencies?

According to both the 1986 and 2011 research, people would most likely find this final sample to be the least unpleasant.  Their determined ranges were slightly different, and I used a sort of median of the two, but the effect essentially stands.

The psychological aspect is interesting but not surprising.  Reuter and his partner Oehler experimented with telling some subjects that a sound, such as fingernails on a chalkboard, was a part of a contemporary musical composition.  Subjects reported a preference for the sounds when they were thought to be musical over when they knew the source. However, measurements of skin conductance indicated that subjects responded with equal distaste, regardless of the perceived source.  This reestablishes the results of a very similar study in 1975 by D.J. Ely using skin potential.

It has also been hypothesized (I haven't yet found confirmation) in these studies that the shape of our auditory canal is such that this middling range of frequencies (about 2-5kHz) is amplified relative to higher and lower frequencies, presumably to aid in hearing people speak.  It seems possible then that even if we were to dislike high and middle frequencies of an ugly sound equally, removing that which is internally amplified thereby removes more total unpleasant sound than removing that which is not amplified.  I propose that the next logical study of this material would attempt to determine the truth of this amplification and then factor the degree of amplification into a comparison of frequency removals, thus determining if there are frequencies that we dislike more than others for no discernable reason.

There are at least two valuable directions that further research could go.  Halpern et al. compared their results to warning calls of macaque monkeys, suggesting zoological, anthropological, and even evolutionary knowledge to be gained from increased understanding of the acoustical properties of animal-generated sounds (Cox's work opposed this theory).  Reuter et al. have suggested that their research could be applied to the commercial arena—perhaps vacuums or other items could be designed to more efficiently sound less unpleasant.  While writing this post, the world's most sensitive smoke alarm went off in my family's house and I couldn't help but wonder if they could be made less irritating with an innovative application of this type of knowledge.  A combination of these studies even suggests that hearing aids could be designed to cut out the most displeasing frequencies of only unpleasant audio.

Of course, musicians will find a way to apply any additional acoustic knowledge to their work.  Therefore, this is totally relevant to my blog.

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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. (Edit: I asked Dr. Reuter about this and received a response, which I discuss in my next post.)



Cox, Trevor J. (2008). Scraping sounds and disgusting noises Applied Acoustics, 69 (12), 1195-1204 DOI: 10.1016/j.apacoust.2007.11.004


Halpern, D.L., Blake R., and Hillenbrand J. (1986). Psychoacoustics of a chilling sound. Perception & psychophysics, 39 (2), 77-80 PMID: 3725541


Kumar, S., Forster, H., Bailey, P., and Griffiths, T. (2008). Mapping unpleasantness of sounds to their auditory representation The Journal of the Acoustical Society of America, 124 (6) DOI: 10.1121/1.3006380


Reuter,  Christoph, and Michael Oehler (2011). Psychoacoustics of chalkboard squeaking. Journal of the Acoustical Society of America, 130 (4), 2545