Path: utzoo!attcan!uunet!rocket!pitaro From: pitaro@rocket.uucp (Michael Pitaro) Newsgroups: comp.dsp Subject: Re: US Gov. sends real-time audio at 2400 baud! Message-ID: Date: 9 Nov 90 13:54:39 GMT References: <1990Nov8.210640.2893@ux1.cso.uiuc.edu> Sender: news@rocket.UUCP Organization: Lockheed Sanders Inc. Lines: 35 In-reply-to: sl35746@uxa.cso.uiuc.edu's message of 8 Nov 90 21:06:40 GMT In article <1990Nov8.210640.2893@ux1.cso.uiuc.edu> sl35746@uxa.cso.uiuc.edu (By-Tor) writes: From: sl35746@uxa.cso.uiuc.edu (By-Tor) Subject: US Gov. sends real-time audio at 2400 baud! Date: 8 Nov 90 21:06:40 GMT Sender: news@ux1.cso.uiuc.edu (News) Hi. I heard that the US government uses 2400 baud modems to send real-time audio, to get a secure line anywhere in the world. Does anyone know what kind of algorithm they are using for compression? I think it would be great if we could make a real-time audio irc for people with sampling/playback capability. Anyways, consider that 2400 baud=2400 bits per second, meaning without compression, you could get 2400 hz sampling at 1 bit resoultion. This is totally unintelligable, so how the heck could they compress it so much? Obviously some kind of destructive method must be used. I thought maybe they look for duplicate waves or something. Any ideas? An example of a secure telephone is a STU III. It uses 1200 bps LPC10-E for voice compression followed by encryption and a REED-SOLOMON block code for error recovery. The voice quality is poor but intelligible. I understand the government is going to upgrade the STU III to use 2400 bps CELP voice compression. Motorola sells one version of the STU III. I hear ATT sells another version. The encryption keys come from the government. I don't know if either company offers a commercial encryption version. The source code for both of these voice compression algorithms (without encryption) can be ordered from NSA for a few hundred dollars. -- ------------------------------------------------------------------------- Michael Pitaro Lockheed Sanders, Inc. Technical Initiative Manager PO Box 2034, MER24-1583 Voice Communications Initiative Nashua, NH 03061-2034 Signal Processing Center of Technology (603)885-9794 (office) (603)885-0631 (fax) e-mail: pitaro@rocket.sanders.com