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Speech coding for security and defense apps, Why do we need very low bitrate?
QuantumKnot
post Jan 18 2006, 03:13
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Hi everyone,

I've heard that ultra low bitrate speech coding (< 800 bps) that use simple modifications to the LPC vocoder (such as segmented LPC vocoders), are of interest mainly for security and defense applications. At such low bitrates, I assume that intelligibility is the only criteria here. My question is why do we need to go to such low bitrates for defense and security? Is it because we want to reserve bandwidth for error-correcting redundancy? Or perhaps encryption? The only thing that I've read which sort of remotely justifies the low bitrate is a lesser chance of being intercepted. huh.gif

If anyone can enlighten me as to why we need such low bitrates (< 800 bps) for security and defense, that would be splendid. smile.gif

Thanks,

QK
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HbG
post Aug 13 2006, 11:30
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I recall bluetooth is a good example of spread spectrum communications, hopping the entire 2.4GHz ISM band.

How you can recieve something when the signal is below the noise level? Doesn't make sense to me.


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Woodinville
post Aug 14 2006, 20:15
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QUOTE (HbG @ Aug 13 2006, 03:30) *
How you can recieve something when the signal is below the noise level? Doesn't make sense to me.


Perhaps you need to consider the meaning of "below the noise level"?

With a narrowband signal, as you narrow the bandwidth, the noise level drops (we're assuming wideband gaussian, for now), does it not?

With a wideband signal, one needs to consider what happens when one compacts (demodulates) the signal, without compacting the noise (which is noise, after all, yes?).


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Posts in this topic
- QuantumKnot   Speech coding for security and defense apps   Jan 18 2006, 03:13
- - clintb   Possibly because they (the men in black) can store...   Jan 18 2006, 04:12
- - boojum   I would ask the people who tell me this stuff. If...   Jan 18 2006, 04:32
|- - Shade[ST]   Why not steganography? At such a low bitrate, you...   Jan 18 2006, 04:48
- - Mike Giacomelli   Bandwidth is a good thing to save whenever you are...   Jan 18 2006, 05:42
|- - QuantumKnot   QUOTE (Mike Giacomelli @ Jan 18 2006, 02:42 P...   Jan 18 2006, 06:24
|- - Shade[ST]   QUOTE (QuantumKnot @ Jan 17 2006, 11:24 PM)QU...   Jan 18 2006, 06:30
- - HotshotGG   QUOTE Why not steganography? At such a low bitrate...   Jan 18 2006, 05:46
- - audio_geek   Do you need lossless eompression for speech commun...   Jan 23 2006, 06:49
- - HbG   The less bandwidth the easier to transmit and thus...   Jan 23 2006, 16:44
|- - pepoluan   QUOTE (HbG @ Jan 23 2006, 10:44 PM)The less b...   Jan 23 2006, 20:10
- - HbG   Actually the global submarine communications trans...   Jan 24 2006, 01:11
- - QuantumKnot   Thanks for the replies everyone. Another reason ...   Feb 9 2006, 23:55
- - Garf   I would say another advantage is that low bitrate ...   Feb 10 2006, 00:20
|- - pepoluan   QUOTE (Garf @ Feb 10 2006, 06:20) I would...   Jun 28 2006, 19:00
|- - Garf   QUOTE (pepoluan @ Jun 28 2006, 20:00) QUO...   Jun 28 2006, 19:07
|- - HbG   QUOTE (pepoluan @ Jun 28 2006, 10:00) QUO...   Jun 28 2006, 19:40
- - jmvalin   QUOTE (QuantumKnot @ Jan 18 2006, 12:13 P...   Apr 10 2006, 16:24
- - HbG   802.11 based wireless networks extend range by swi...   Jun 28 2006, 01:49
- - maxonen   QUOTE (QuantumKnot @ Jan 18 2006, 04:13) ...   Aug 9 2006, 14:58
|- - kwwong   QUOTE (maxonen @ Aug 9 2006, 08:58) QUOTE...   Aug 13 2006, 08:26
|- - Garf   QUOTE (kwwong @ Aug 13 2006, 09:26) QUOTE...   Aug 13 2006, 10:49
|- - kwwong   QUOTE (Garf @ Aug 13 2006, 04:49) QUOTE (...   Aug 14 2006, 11:55
- - Woodinville   Because the channels they use for communications a...   Aug 9 2006, 19:01
- - HbG   I recall bluetooth is a good example of spread spe...   Aug 13 2006, 11:30
|- - Woodinville   QUOTE (HbG @ Aug 13 2006, 03:30) How you ...   Aug 14 2006, 20:15
|- - kwwong   QUOTE (Woodinville @ Aug 14 2006, 14:15) ...   Sep 3 2006, 09:30
- - beto   It's against common sense but it works. See CD...   Aug 13 2006, 15:07
- - cabbagerat   I think Garf's theory that it is to avoid dire...   Sep 3 2006, 13:09
- - DonP   Another consideration, and I really don't know...   Nov 9 2010, 14:20


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