Building a Time Machine for Radio

The Radio Spectrum Archive will let you listen to old broadcasts as if they were live

3 min read
Image of a a spectrum recording of the AM band, originally recorded on VHS tape in 1986
Radio Rewind: This is a spectrum recording of the AM band, originally recorded on VHS tape in 1986. Individual stations can be easily seen as spikes along this digitized sample.
Image: The Radio Spectrum Archive

Thomas Witherspoon is building a time machine, of sorts. With it, you’ll be able to pick a date and tune through an entire broadcast band as if you had a radio that could pick up transmissions from the past. Sure, well-established shows already make past episodes available, but with Witherspoon’s time machine you’ll be able to hear not just that programming but everything else that was on the air as well: the local news, the commercials, the pirate stations, even the mysterious number stations that lurk on shortwave.

Witherspoon’s time machine is The Radio Spectrum Archive. The technological advance that makes it possible is the proliferation in recent years of cheap software-defined radios (SDRs), which can digitize enormous swaths of radio spectrum. The SDR’s software can be used to select individual transmissions and listen to them live. Or the swath of spectrum can be recorded and played back through the software later, letting listeners tune into broadcasts just as if they were live.

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From WinZips to Cat GIFs, Jacob Ziv’s Algorithms Have Powered Decades of Compression

The lossless-compression pioneer received the 2021 IEEE Medal of Honor

11 min read
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Photo of Jacob Ziv
Photo: Rami Shlush
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Lossless data compression seems a bit like a magic trick. Its cousin, lossy compression, is easier to comprehend. Lossy algorithms are used to get music into the popular MP3 format and turn a digital image into a standard JPEG file. They do this by selectively removing bits, taking what scientists know about the way we see and hear to determine which bits we'd least miss. But no one can make the case that the resulting file is a perfect replica of the original.

Not so with lossless data compression. Bits do disappear, making the data file dramatically smaller and thus easier to store and transmit. The important difference is that the bits reappear on command. It's as if the bits are rabbits in a magician's act, disappearing and then reappearing from inside a hat at the wave of a wand.

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