← Back to context

Comment by dllu

9 years ago

Shaking things often fixes problems. This reminds me of the following story:

> [O]ne of the earliest [applications] of dither came in World War II. Airplane bombers used mechanical computers to perform navigation and bomb trajectory calculations. Curiously, these computers (boxes filled with hundreds of gears and cogs) performed more accurately when flying on board the aircraft, and less well on ground. Engineers realized that the vibration from the aircraft reduced the error from sticky moving parts. Instead of moving in short jerks, they moved more continuously. Small vibrating motors were built into the computers, and their vibration was called dither from the Middle English verb "didderen," meaning "to tremble." Today, when you tap a mechanical meter to increase its accuracy, you are applying dither, and modern dictionaries define dither as a highly nervous, confused, or agitated state. In minute quantities, dither successfully makes a digitization system a little more analog in the good sense of the word.

— Ken Pohlmann, Principles of Digital Audio

7 comments

dllu

Reply
Fnoord  9 years ago

> Shaking things often fixes problems.

Oh, indeed. I remember my father, a disabled former engineer, having an expensive McIntosh audio system. He was always fiddling with it, fixing it, applying anti oxidation spray, etc. My parents decided the large wall furniture (in which the audio system was, together with books, TV, etc) was to be replaced.

It turned out that during the giant relocation one of the compartments of his system (IIRC it was the tuner, but it might have been the pre-amplifier or amplifier as well) had become broken. My father, who was nearly blind, made it his project to repair the installation. He was failing, and my parents discussed sending the broken part of the audio system back for repair which would set us back a large sum of money.

Then, at some point, there was an earthquake of 5,5 on the Richter scale. (Having just looked it up the epicenter being 5,8 it was the largest earthquake ever registered in The Netherlands.)

The damage: a photo of a family member, protected by glass, had fallen and the glass was broken. In our wall, a rift appeared. Many things just weren't on their correct place. The radio? Ah, the radio. It worked again when it was put on!!

mikeash  9 years ago

A similar phenomenon occurs with aircraft altimeters. They move smoothly in small propellor planes but tend to stick and then jump maybe 50ft at a time in gliders. Tapping the altimeter is standard procedure if you want to see small movements.