Oona Räisänen has written a thorough and engrossing article about the noises emitted by dial-up modems while they connect and handshake, and the accompanying graphic (ZOMG HUGE) is nothing short of spectacular. It would make a great full-size poster -- maybe a framed art-print.
Now the modems must address the problem of echo suppression. When humans talk, only one of them is usually talking while the other one listens. The telephone network exploits this fact and temporarily silences the return channel to suppress any confusing echoes of the talker's own voice.
Modems don't like this at all, as they can very well talk at the same time (it's called full-duplex). The answering modem now puts on a special answer tone that will disable any echo suppression circuits on the line. The tone also has periodic "snaps" (180° phase transitions) that aim to disable yet another type of circuit called echo canceller.
Now the modems will list their supported modulation modes and try to find one that both know. They also probe the line with test tones to see how it responds to tones of different frequencies, and how much it attenuates the signal. They exchange their test results and decide a speed that is suitable for the line.
After this, the modems will go to scrambled data. They put their data through a special scrambling formula before transmission to make its power distribution more even and to make sure there are no patterns that are suboptimal for transfer. They listen to each other sending a series of binary 1's and adjust their equalizers to optimally shape the incoming signal.
The sound of the dialup, pictured
Veteran reviewer/interviewer Rick Kleffel (previously) has just posted a long podcast interview (MP3) with Neal Stephenson, discussing his latest novel, Fall; or, Dodge in Hell ("a science fiction novel with a fantasy novel stuck inside of it").
A couple of weeks ago, I was thrilled to hear Subgenius founder, the Reverend Ivan Stang, interviewed on the Comedy on Vinyl podcast (previously) and to discover that the Church of the Subgenius was selling a $35 Salvation/Membership/Ordainment kit that was chock full of goodies.
[Randall Munroe traces the phenomenal success of his webcomic XKCD with this Boing Boing post; and I've avidly followed his career ever since (he's returned the favor), so I was delighted to learn in February that he had a new book coming out and I'm more delighted still to host the official announcement of his […]
Whether you’re an artist, designer or just organizing a photo album, photo editing software is a must. And software designers know it: Platforms like Photoshop and Lightroom have a ton of helpful features, but you’ll pay for them in spades. Luckily, there’s some competition in the photo editing arena. Right now, Skylum’s Luminar software is […]
Who needs a holiday sale? Sometimes there’s no better time than the thick of summer to find deals. We should know – we’ve found ten deep discounts on some must-have items. Whether you’re searching for CBD edibles, exercise gear, chargers or other tech, take a look. But don’t look long – these prices aren’t likely […]
Heading abroad? Even if it’s just a short trip, there’s a lot to prepare for. Travel can be incredibly rewarding, but it can tricky to navigate different cultures and lodging arrangements – and even trickier to do it cheaply. Before you go shopping for suitcases, here’s our pick for a good first investment: The Ultimate […]