4 ms·

How Margaret Thatcher's secret Brahms phone was invented

15 points by timthorn 4y ago

ggm 4y ago
One time pad on tape. Not bad. Like all one time pads, it has a pad renewal requirement and an absolute no reuse requirement. 2400 baud probably meant lpc, linear predictive encoding, I was told designed for VLF comms to submarines and also sent everywhere worldwide as a very strongly penetrative wave, but slow slow slow. So..also one time pad. More room on a sub for boxes but same one time key distribution problem. Lpc used a speech model. Probably, the model lacked female voices so encoded for a lower male voice register. Thatcher famously had voice coaching. To lower her shrill tones. I doubt it was to optimise for this device. I hated Thatcher, always voted against her. She was (in my biassed opinion) a highly effective unloveable divisive leader.
kazinator 4y ago
> 2.4 kilobytes per second (the UK's current average broadband speed is more than 21,000 times faster). Is that figure right, and not mixing up bits and bytes? That's actually heck of a lot, especially for the era: it's a whopping 19.2 kbps. Today, you could use some wide-band voice codecs at that rate. Consumers didn't have 19.2 kbps modems until 1990 something.
- Canada 4y ago
  Compression techniques have vastly improved improved since those days. Encoding requires fast processing to be done in realtime. I didn't check their math, but we sure weren't streaming audio with our 2400 or 9600 baud modems back then, and we couldn't encode mp3s at play speed on our PCs in the early 1990s.
  - timthorn 4y ago
    LPC certainly worked at 2400 baud in that timeframe. Given that the line interface was typically an acoustic coupler in the early 90s, I'm pretty sure that 2400 baud and not 2.4kBps was the actual bit rate.
    - Canada 4y ago
      How did it sound?
      - timthorn 4y ago
        Not great! It could require some concentration to decipher. The codec is based on a model of the vocal tract so encoding anything other than voice gives very poor results. There are some good examples of 2.4kbps LPC10 on this page: http://www0.cs.ucl.ac.uk/teaching/GZ05/samples/ http://www0.cs.ucl.ac.uk/teaching/GZ05/samples/

15 points by timthorn 4y ago

ggm 4y ago

One time pad on tape. Not bad. Like all one time pads, it has a pad renewal requirement and an absolute no reuse requirement. 2400 baud probably meant lpc, linear predictive encoding, I was told designed for VLF comms to submarines and also sent everywhere worldwide as a very strongly penetrative wave, but slow slow slow. So..also one time pad. More room on a sub for boxes but same one time key distribution problem. Lpc used a speech model. Probably, the model lacked female voices so encoded for a lower male voice register. Thatcher famously had voice coaching. To lower her shrill tones. I doubt it was to optimise for this device. I hated Thatcher, always voted against her. She was (in my biassed opinion) a highly effective unloveable divisive leader.

kazinator 4y ago

> 2.4 kilobytes per second (the UK's current average broadband speed is more than 21,000 times faster). Is that figure right, and not mixing up bits and bytes? That's actually heck of a lot, especially for the era: it's a whopping 19.2 kbps. Today, you could use some wide-band voice codecs at that rate. Consumers didn't have 19.2 kbps modems until 1990 something.

Canada 4y ago
Compression techniques have vastly improved improved since those days. Encoding requires fast processing to be done in realtime. I didn't check their math, but we sure weren't streaming audio with our 2400 or 9600 baud modems back then, and we couldn't encode mp3s at play speed on our PCs in the early 1990s.
- timthorn 4y ago
  LPC certainly worked at 2400 baud in that timeframe. Given that the line interface was typically an acoustic coupler in the early 90s, I'm pretty sure that 2400 baud and not 2.4kBps was the actual bit rate.
  - Canada 4y ago
    How did it sound?
    - timthorn 4y ago
      Not great! It could require some concentration to decipher. The codec is based on a model of the vocal tract so encoding anything other than voice gives very poor results. There are some good examples of 2.4kbps LPC10 on this page: http://www0.cs.ucl.ac.uk/teaching/GZ05/samples/ http://www0.cs.ucl.ac.uk/teaching/GZ05/samples/