One of the most common sounds in the modern world is the beep. From microwaves and cellphones to computers and backing-up trucks, this high-pitched alert pings us from every direction. But how is it made, and why is it so grating?
"In order to make sounds, you basically have to vibrate a surface," said Robert White, a professor of mechanical engineering at Tufts University.
Artificial sounds are typically produced using one of two devices — a cone and magnetic coil speaker, which amplifies the sound from a vibrating magnet, or a piezoelectric speaker, made with special materials that change shape when exposed to an electric current.
From an electronics standpoint, it is easy to generate a beep sound, White said. All it takes to make a beep is a common electric circuit that produces a square wave, a simple type of signal that jumps back and forth between two levels, and a speaker to amplify it.
"If you take that square wave and throw it at a piezoelectric speaker or a magnetic coil type speaker, it will make a sound that is more less a pure tone with overtones, which is that beeping sound," White told Life's Little Mysteries.
The method doesn't require any computation, and was easy to perform even before most electronic devices contained computer chips. It is also inexpensive, because low-quality piezoelectric buzzers are cheap to manufacture. "For something commercial, it has to be cheap," White said, "so the cheaper it is, the worse the quality is going to be in terms of the sound."
"So much of design is dictated on budget," said Patrick Fenton, who is a designer at the Swayspace design studio and a teacher of industrial design at Pratt Institute in New York. It would take a designer with a passion for audio to advocate for more money to be put toward sound design, he said.
In short, beeps are cheap. Fenton said this is probably the main reason they've remained common in computer applications and other devices, even ones that contain higher-quality speakers capable of making more nuanced sounds.
Zero to 60 in zero seconds
Having spent most of our time evolving prior to the invention of smoke detectors, elevators and the like, our brains can't quite grasp beep sounds, so they irritate us. "There's just something fundamentally different about the way your brain is processing sounds with natural envelopes," said Michael Schutz, assistant professor of music at McMaster University in Ontario and a researcher at the McMaster Institute for Music and the Mind.
In the analog world, sound is created from a transfer of energy, often from one object striking another, such as a stick hitting a drum, Schutz explained. In that case, energy is transferred into the drum and then gradually fades away."The sound has to decay," Schutz said, "and our perceptual system as it's evolved, I think it has really latched on to that as a useful way of understanding the event."
The way a natural sound gradually fades is one factor that our brains use to figure out what made it. But the flat tone of a beep lacks that fadeaway, or any other small variations of a natural sound. "Flat tones are basically incompatible with the physical reality of the natural world," Schutz said. [Why Do Fingernails on Chalkboard Make Us Cringe?]
He compared a flat beep sound to a car driving 60 mph then suddenly hitting a wall, as opposed to gradually slowing to a stop.
"I suspect that's why the flat tones sound fishy, it's that lack of change over time, both with the sustain period just sort of sitting there, and then with that offset, basically going from 60 mph to 0 without gradually slowing down," Schutz said.
While it might be helpful for sounds that warn of danger to be shrill and unnatural, lots of beeps could be avoided. Schutz pointed out that many cellphones and other devices these days are already using more natural-sounding tones. "A company like Apple, that handles a good portion of their design in-house, is able to take a look at every single aspect of the design," said Fenton, adding that the process allows them to concentrate on sound far more than most design firms.
"It's probably an underresearched and underexploited area in design," Fenton said of high-quality audio alerts — and one he thinks will start seeing more attention.
Research shows the effort might well pay off. In an unpublished study, Schutz showed participants two different cellphones. The phones played a series of the same four tones when a call was missed, but one used artificial flat tones and the other used tones that had a more natural decay. Close to 90 percent of participants preferred the phone that used the natural tones.
"People were willing to pay appreciably more, and they like the product better, so from a product standpoint, I think there is a lot to be gained from exploring this," Schutz said.
Anthony McGovern is a New York-based freelance science and technology writer. He covers green technology, innovative use of game design and brain science.
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