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Há que fazer a ressalva, o codec (vocoder mais correctamente) não é
propriamente para SSB e pode ter muitas aplicações, o ser mencionado
o SSB tem a ver com o facto de por tão reduzido ser o bitrate usado
torna-o passível de ser usado nos reduzidos canais SSB.<br>
No entanto, para ser viável a sua utilização por exemplo em HF onde
se usa mais o SSB, necessitará de bem mais bits para possibilitar a
correcção de falhas temporárias de perdas de tramas (QSB ou
QRM/QRN), aquilo que se designa genericamente de FEC.<br>
Na comparação com o AMBE usado do DStar há que ter esse pormenor em
conta porque, se não me falha a memória, o AMBE já inclui FEC e este
vocoder sendo genérico creio não incluir, terá de ter uma camada
adicional que o adicione.<br>
<br>
Mais informação:<br>
Vocoder - <a class="moz-txt-link-freetext" href="http://en.wikipedia.org/wiki/Vocoder">http://en.wikipedia.org/wiki/Vocoder</a><br>
Codec2 - <a class="moz-txt-link-freetext" href="http://www.rowetel.com/blog/?page_id=452">http://www.rowetel.com/blog/?page_id=452</a><br>
FEC - <a class="moz-txt-link-freetext" href="http://en.wikipedia.org/wiki/Forward_error_correction">http://en.wikipedia.org/wiki/Forward_error_correction</a><br>
AMBE - <a class="moz-txt-link-freetext" href="http://en.wikipedia.org/wiki/Advanced_Multi-Band_Excitation">http://en.wikipedia.org/wiki/Advanced_Multi-Band_Excitation</a><br>
<br>
73!<br>
<br>
On 16-11-2011 14:16, João Gonçalves Costa wrote:
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<p class="MsoNormal"><span lang="EN-US">Amateur Radio 1400 bps
Digital Voice CODEC<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">In his blog David Rowe
VK5DGR describes the work being done in developing a Digital
Voice CODEC that works at 1400 bps.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The development of a
1400 bps CODEC paves the way for future Amateur Radio
digital voice systems using potentially as little as half
the bandwidth of a traditional SSB signal.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">In his blog David says:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">"Building a 1400 bit/s
communications quality speech codec is a highlight of my
career."<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">"The CELP based speech
codecs I built in the early 90's could deliver
communications quality speech at 9600 bit/s, or (with a
significant drop in quality) run at 4800 bit/s. So managing
to get about the same quality at 1400 bit/s is a nice
personal achievement for me. Giving it away to the world is
even cooler."<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Read the David Rowe
VK5DGR blog at<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><a class="moz-txt-link-freetext" href="http://www.rowetel.com/blog/?p=2255">http://www.rowetel.com/blog/?p=2255</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Join the Codec2 email
list at<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><a class="moz-txt-link-freetext" href="https://lists.sourceforge.net/lists/listinfo/freetel-codec2">https://lists.sourceforge.net/lists/listinfo/freetel-codec2</a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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QRA: Pedro Ribeiro // Callsign: CR7ABP // GRID Locator: IM58mr
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# HAM operation very limited by class 3 rules until April 2012 #
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