3 expanded posts ยท every known parent and child
> From: Brad Huntting <huntting@glarp.com> > > It would seem that both the sender and reciever need to be exactly > syncronized to within 1/4 of a bit for this to work. Since voice > data requires about 64Khz Just as a point of information, you can compress voice into 4kbit/sec without any real loss of quality. Perry
> > ... voice data requires about 64Khz... Actually I think you meant 64 kbits/sec. > Just as a point of information, you can compress voice into 4kbit/sec > without any real loss of quality. I wouldn't say "without any real loss of quality". I have an AT&T secure phone on loan for evaluation (attendees at the last Mt. View cypherpunks meeting have played with it). It compresses voice to 4800 b/s then encrypts it and uses a stripped down V.32 modem to send it. The voice is intelligible on the other end, but there is definitely a loss of quality. It sounds like you are talking through the bubbler in an aquarium (underwater). But it is possible to recognize someone's voice on the other end, at least when you already know who it is. "No real loss of quality" goes way too far. By the way, I have public domain (federally written) code that compresses voice down to this size. It's called CELP, Code Excited Linear Prediction. The only catch is the code they wrote runs much slower than realtime (on workstations). My guess is that there are significant speedups that we could make by hacking on it and running gprof. Van Jacobson has done some work on this, but his policy seems to be to sit on anything good for two to three years before releasing it. Anyone interested in beating him to the net with something that would compress voice (or voicemail) in realtime on a 486 or a SPARC? John
> Just as a point of information, you can compress voice into 4kbit/sec > without any real loss of quality. GSM uses 11.5 kbit/s. GSM is also supposed to provide a digital 9600 bd async connection, but I have not yet seen any implementations of data GSM. Some manufacturers are promising to ship products supporting it during 1993... Julf