Andrew Carol, a software developer for Apple Computer Inc., Cupertino, Calif., and a self-described "engineering fiend," had for years been enamored of the idea of building a 19th-century difference engine out of Lego pieces. One of the earliest conceptions of a mechanical computer, a difference engine is a machine for solving polynomial equations. (For those of you who have forgotten, those are equations such as f ( x ) = Ax2 + Bx + C .) Initially, he took the most famous example as inspiration, Charles Babbage's Difference Engine No. 2, which was sketched out in 1822 but finally built only in 1991, at the London Science Museum.

"That's what held me up," Carol says. Engine No. 2 relies on lots of vertical rods for translating information between the machine's components. The plastic Legos were too soft for the task. But Babbage's earlier design, No. 1, while more complex, works with gears, and Lego has gears aplenty. Once Carol had managed to get a key component working--a mechanical adder that retains the numbers being added--it took him three months to build his own, all-Lego, difference engine (

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Deep Learning Could Bring the Concert Experience Home

The century-old quest for truly realistic sound production is finally paying off

12 min read
Image containing multiple aspects such as instruments and left and right open hands.
Stuart Bradford

Now that recorded sound has become ubiquitous, we hardly think about it. From our smartphones, smart speakers, TVs, radios, disc players, and car sound systems, it’s an enduring and enjoyable presence in our lives. In 2017, a survey by the polling firm Nielsen suggested that some 90 percent of the U.S. population listens to music regularly and that, on average, they do so 32 hours per week.

Behind this free-flowing pleasure are enormous industries applying technology to the long-standing goal of reproducing sound with the greatest possible realism. From Edison’s phonograph and the horn speakers of the 1880s, successive generations of engineers in pursuit of this ideal invented and exploited countless technologies: triode vacuum tubes, dynamic loudspeakers, magnetic phonograph cartridges, solid-state amplifier circuits in scores of different topologies, electrostatic speakers, optical discs, stereo, and surround sound. And over the past five decades, digital technologies, like audio compression and streaming, have transformed the music industry.

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