So, the Mr. Charliemobile had to go into the shop today. At the end of the day I got a ride from the shop’s driver, Sam. Sam’s job is to drive around all day, carrying people from the shop to their work and then from their work back to the shop. He uses a cell phone frequently and has people call him to get picked up, etc. It’s a nice example of distributed control. He don’t need no stinkin’ receptionist to schedule the routes. Just call him, and he’ll fit you in just as soon as he can.
Sam is a perfect stand-in for Kramer on Seinfeld, and probably in the off-hours has a a lot of stories to tell about life on the local road. When he picked me up this afternoon, the front seat was free, and Sam had some painfully bogus music on the tinny sound system. I could have helped him out with some kind CDs I had in my briefcase, but he was commenting on the skills and education of proximate drivers and I felt it might disrupt his Wa. Plus, I didn’t want to freak out Don, an engineer from CRREL (no website, apparently), in the back seat. So we listened to oldies or somesuch dreck driving to the shop.
Driving through downtown, Sam commented on a shortcut that happend to be in a neighborhood where my wife and I lived for four years. We compared notes on which of the two methods to implement the shortcut is best. After four years of research, I’m sure that method two is best, except from 7:30 AM to 8:15 AM, when the high school is filling. The winner is not obvious. The difference between them is only perhaps 10 – 30 seconds, but if you’re driving around all day, saving 30 seconds here and there and feeling like you won a minor battle isn’t all bad.
So anyway, at some point in the 20 minute drive, Sam’s cell phone rings. What happened next was a case study in efficiency and learned optimization. Instantly, Sam turned the radio off; he picked up the cell phone with his right hand and handed it off to his left; rolled down my window (right side) about two inches (key point); took the call using his left ear and made arrangements to pick someone up after he dropped us off. When the call ended he hung up, rolled up the window and turned the radio back on.
Test Question: Why did Sam roll down the right side window and use his left ear to listen?
Answer: Binaural Masking Level Difference. I kid you not.
Sam doesn’t know the first thing about psychoacoustics or the BMLD, but I can tell you definitively that what Sam had learned from frequent experience is that a small amount of noise added to the opposite ear will improve the signal to noise ratio and the intelligibility of voices.
I asked him if he ever rolled down both windows when he got a call. “Nope, that doesn’t work as well. I’ve tried it both ways. If I use my left ear I roll down the right window.” Has he ever tried using his right ear and rolling down his left window? “Tried it, but that window is too close to my head, so the noise is too loud, even if I roll it down just a little. Plus, my hearing’s better in my left ear. Know how I found out? One night I was lying in bed on my right side and I could hear everything just normal. Then I rolled over and my left ear was in the pillow and my right ear was up and everything was kind of muffled and distant. It’s easier to go to sleep lying on my left side. It’s weird that rolling down the window helps me hear on the phone, but it’s a lot better.”
What we were having here is a human conversation, sharing, learning, no defenses, no ego.
I explained a bit about the BMLD, and how it could improve intellibility by “6 dB,” which is four times as good as without the window, so it didn’t surprise me, but I had never seen anyone use the BMLD in daily life
July 21, 2003