Excellent BBC program about forensic phonetics

I don’t usually reblog things, but this is an excellent program on the use of forensic phonetics in Britain.


Which are better, earphones or headphones?

As a phonetician, it’s part of my job to listen to sounds very closely. Plus, I like to listen to music while I work, enjoy listening to radio dramas and use a headset to chat with my guildies while I’m gaming.  As a result, I spend a lot of time with things on/in my ears. And, because of my background, I’m also fairly well informed about the acoustic properties of  earphones and headphones and how they interact with anatomy. All of which helps me answer the question: which is better? Or, more accurately, what are some of the pros and cons of each? There are a number of factors to consider, including frequency response, noise isolation, noise cancellation and comfort/fit. Before I get into specifics, however, I want to make sure we’re on the same page when we talk about “headphones” and “earphones”.

Earphones: For the purposes of this article, I’m going to use the term “earphone” to refer to devices that are meant to be worn inside the pinna (that’s the fancy term for the part of the ear you can actually see). These are also referred to as “earbuds”, “buds”, “in-ears”, “canalphones”, “in-ear moniters”, “IEM’s” and “in-ear headphones”. You can see an example of what I’m calling “earphones” below.

IPod Touch 2G Remote Mic
Ooo, so white and shiny and painful.

Headphones: I’m using this term to refer to devices that are not meant to rest in the pinna, whether they go around or on top of the ear. These are also called “earphones”, (apparently) “earspeakers” or, my favorites, “cans”. You can see somewhat antiquated examples of what I’m calling “headphones” below.

Club holds radio dance wearing earphones 1920
I mean, sure, it’s a wonder of modern technology and all, but the fidelity is just so low.

Alright, now that we’ve  cleared that up, let’s get down to brass tacks. (Or, you might say…. bass tacks.)

  1. Frequency response curve: How much distortion do they introduce? In an ideal world, ‘phones should responded equally well to all frequencies (or pitches), without transmitting one frequency rage more loudly than another. This desirable feature is commonly referred to as a “flat” frequency response. That means that the signal you’re getting out is pretty much the same one that was fed in, at all frequency ranges.
    1. Earphones: In general, earphones tend to have a worse frequency response.
    2. Headphones: In general, headphones tend to have better frequency response.
    3. WinnerHeadphones are probably the better choice if you’re really worried about distortion. You should read the specifications of the device you’re interested in, however, since there’s a large amount of variability.
  2. Frequency response: What is their pitch range? This term is sometimes used to refer to the frequency response curve I talked about above and sometimes used to refer to pitch range. I know, I know, it’s confusing. Pitch range is usually expressed as the lowest sound the ‘phones can transmit followed by the highest. Most devices on the market today can pretty much play anything between 20 and 20k Hz. (You can see what that sounds like here. Notice how it sounds loudest around 300Hz? That’s an artifact of your hearing, not the video. Humans are really good at hearing sounds around 300Hz which [not coincidentally] is about where the human voice hangs out.)
    1. Earphones: Earphones tend to have a smaller pitch range than headphones. Of course, there are always exceptions.
    2. Headphones: Headphones tend to have a better frequency range than earphones.
    3. Winner: In general, headphones have a better frequency range. That said, it’s not really that big of a deal. You can’t really hear very high or very low sounds that well because of the way your hearing system works regardless of how well your ‘phones are delivering the signal. Anything that plays sounds between 20Htz and 20,000Htz should do you just fine.
  3. Noise isolation: How well do they isolate you from sounds other than the ones you’re trying to listen to? More noise isolation is generally better, unless there’s some reason you need to be able to hear environmental sounds as well whatever you’re listening to. Better isolation also means you’re less likely to bother other people with your music.
    1. Earphones:  A properly fitted pair of in-ear earphones will give you the best noise isolation. It makes sense; if you’re wearing them properly they should actually form a complete seal with your ear canal. No sound in, no sound out, excellent isolation.
    2. Headphones: Even really good over-ear headphones won’t form a complete seal around your ear. (Well, ok, maybe if you’re completely bald and you make some creative use of adhesives, but you know what I mean.) As a result, you’re going to get some noise leakage .
    3. Winner: You’ll get the best noise isolation from well-fitting earphones that sit in the ear canal.
  4. Noise cancellation: How well can they correct for atmospheric sounds? So noise cancellation is actually completely different from noise isolation. Noise isolation is something that all ‘phones have. Noise-cancelling ‘phones, on the other hand, actually do some additional signal processing before you get the sound. They “listen” for atmospheric sounds, like an air-conditioner or a car engine. Then they take that waveform, reproduce it and invert it. When they play the inverted waveform along with your music, it exactly cancels out the sound. Which is awesome and space-agey, but isn’t perfect. They only really work with steady background noises. If someone drops a book, they won’t be able to cancel that sudden, sharp noise. They also tend not to work as well with really high-pitched noises.
    1. Earphones: Noise-cancelling earphones tend not be as effective as noise-cancelling headphones until you get to the high end of the market (think $200 plus).
    2. Headphones: Headphones tend to be slightly better at noise-cancellation than earphones of a similar quality, in my experience. This is partly due to the fact that there’s just more room for electronics in headphones.
    3. Winner: Headphones usually have a slight edge here. Of course, really expensive noise-cancelling devices, whether headphones or earphones, usually perform better than their bargain cousins.
  5. Comfort/fit: Is they comfy?
    1. Earphones: So this is where earphones tend to suffer. There is quite a bit of variation in the shape of the cavum conchæ, which is the little bowl shape just outside your ear canal. Earphone manufacturers have to have somewhere to put their magnets and drivers and driver support equipment and it usually ends up in the “head” of the earphone, nestled right in your concha cavum. Which is awesome if it’s a shape that fits your ear. If it’s not, though, it can quickly start to become irritating and eventually downright painful. Personally, this is the main reason I prefer over-ear headphones.
    2. Headphones: A nicely fitted pair of over-ear headphones that covers your whole ear is just incredibly comfortable. Plus, they keep your ears warm! I find on-ear headphones less comfortable in general, but a nice cushy pair can still feel awesome. There are other factors to take into account, though; wearing headphones and glasses with a thick frame can get really uncomfortable really fast.
    3. Winner: While this is clearly a matter of personal preference, I have a strong preference for headphones on this count.

So, for me at least, headphones are the clear winner overall. I find them more comfortable, and they tend to reproduce sound better than earphones. There are instances where I find earphones preferable, though. They’re great for travelling or if I really need an isolated signal. When I’m just sitting at my desk working, though, I reach for headphones 99% of the time.

One final caveat: the sound quality you get out of your ‘phones depends most on what files you’re playing. The best headphones in the world can’t do anything about quantization noise (that’s the noise introduced when you convert analog sound-waves to digital ones) or a background hum in the recording.

Is dyslexia genetic?

I’m a graduate student in linguistics. I have a degree in English literature. I love reading, writing and books with the fiery passion of a thousand suns. And I am dyslexic. While I was very successfully academically in secondary and higher education, let’s just say that primary school was… rough. I’ve failed enough spelling tests that I could wallpaper a small room with them. At this point I’m a fluent reader, mainly because no one’s asking me to read things without context. (For an interesting experimental look at the effects of world-knowledge and context on reading, I’d recommend Paul Kolers 1970 article, “Three stages of reading”.) These days, language processing problems tend to be flashes in the pan rather than a constant barrier I’m pushing against. I tend to confused “cloaca” and “cochlea”, for example, and I feel like I use “etymology” and “entomology” correctly at chance. But still, it would be nice to know that my years of suffering in primary school were due to genetic causes and not because I was “dumber” or “lazier” than other kids. And recent research does seem to support that: it looks like dyslexia probably is genetic.

Dyslexic words
They all look good to me.

First off, a couple caveats. Dyslexia is an educational diagnosis. There’s a pretty extensive battery of tests, any of which may be used to diagnose dyslexia. The International Dyslexia Association defines dyslexia thusly:

It is characterized by difficulties with accurate and / or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge.

Which sounds pretty standard, right? But! There are a number of underlying causes that might lead to this. One obvious one is an undiagnosed hearing problem. Someone who only has access to part of the speech signal will probably display all of these symptoms. Or someone in an English-only environment who speaks, say, Kola, as their home language. It’s hard to learn that ‘p’ means /p/ if your language doesn’t have that sound. Of course, educators know that these things affect reading ability. But there are also a number of underlying mental processes that might lead to a diagnosis of dyslexia, which may or may not be related to each other but are all almost certainly genetic. Let’s look at a couple of them.

  • Phonological processing. I’ve talked a little bit about phonology before. Basically, someone with phonological disorder has a hard time with language sounds specifically. For example, they may have difficulty with rhyming tasks, or figuring out how many sounds are in a word. And this does seem to have a neurological compontent. One study shows that, when children with dyslexia were asked to come up with letters that rhymed, they did not show activity in the Temporoparietal junction, unlike their non-dyslexic peers. Among other things, the Temporoparietal junction plays a role in interpreting sequences of events.
  • Auditory processing. Auditory processing difficulties aren’t necessarily linguistic in nature. Someone who has difficulty processing sounds may be tone deaf, for example, unable to tell whether two notes are the same or different. For dyslexics, this tends to surface as difficulty with sounds that occur very quickly. And there’s pretty much no sounds that humans need to process more quickly than speech sounds. A flap, for example, lasts around 20 milliseconds. To put that in perspective, that’s about 15 times slower than a fast blink. And it looks like there’s a genetic cause for these auditory processing problems: dyslexic brains have a localized asymmetry in their neurons. They also have more, and smaller neurons.
  • Sequential processing. For me, this is probably the most interesting. Sequential processing isn’t limited to language. It had to do with doing or perceiving things in the correct order. So, for example, if I gave you all the steps for baking a cake in the wrong order, you’d need to use sequential processing to put them in the correct order. And there’s been some really interesting work done, mainly by Beate Peter at the University of Washington (represent!) that suggests that there is a single genetic cause responsible for a number of rapid sequential processing task, and one of the effects of an abnormality in this gene is dyslexia. But people with this mutation also tend to be bad at, for example, touching each of their fingers to their thumb in order. 
  • Being a dude. Ok, this one is a little shakier, but depending on who you listen to, dyslexia is either equally common men and women, 4 to 5 times more common in men or 2 to 3 times more common in men. This may be due to structural differences, since it seems that male dyslexics have less gray matter in language processing centers, whereas females have less gray matter in sensing and motor processing areas. Or the difference could be due to the fact that estrogen does very good things for your brain, especially after traumatic injury. I include it here because sex is genetic (duh) and seems to (maybe, kinda, sorta) have an effect on dyslexia.

Long story short, there’s been quite a bit of work done on the genetics of dyslexia and the evidence points to a probably genetic common cause. Which in some ways is really exciting! That means that we can predict better who will have learning difficulties and work to provide them with additional tutoring and help. And it also means that some reading difficulties are due to anatomy and genes. If you’re dyslexic, it’s because you’re wired that way, and not because your parents did or didn’t do something (well, other than contribute your genetic material, obvi) or because you didn’t try hard enough. I really wish I could go back in time and tell that to my younger self after I completely failed yet another spelling test, even though I’d copied the words a hundred times each

But the genetic underpinning of dyslexia might also seem like a bad thing. After all, if dyslexia is genetic, does that mean that children with reading difficulties will just never get over them? Not at all! I don’t have space here to talk about the sort of interventions and treatments that can help dyslectics. (Perhaps I’ll write a future post on the subject.) Suffice to say, the dyslexic brain can learn to compensate and adapt over time. Like I said above, I’m currently a very fluent reader. And dyslexia can be a good thing. The same skills that can make learning to read hard can make you very, very good at picking out one odd thing in a large group, or at surveying a large quantity of visual information quickly — even if you only see it out of the corner of your eye. For example, I am freakishly good at finding four-leaf clovers. In high school, I collected thousands of them just while doing chores around the farm. And that’s not the only advantage. I’d recommend the Dyslexic Advantage (it’s written for a non-scientific audience) if you’re interested in learning more about the benefits of dyslexia. The authors point out that dyslectics are very good at making connections between things, and suggest that they enjoy an advantage when reasoning spatially, narratively, about related but unconnected things (like metaphors) or with incomplete or dynamic information.

The current research suggests pretty strongly that dyslexia is something you’re born with. And even though it might make some parts of your school career very difficult, it won’t stop you from thriving. It might even end up helping you later on in life.