Tony wrote: > Ed wrote: > > > Are there any communications engineers in this group that can give > > us some idea whether a useable quality digitized voice can be sent > > over a 2.5 KHz wide HF channel with SNR comparable to or less > > > than what is required for analog voice? > > I was thinking about this today Ed. I'd sacrifice a bit of voice > qaulity for better SNR performance. > > WinDRM defaults to the MELP codec and I was wondering if the SPEEX or > LP-10 offer an improvement in SNR performance? > > Tony KT2Q
Whatever you do to reduce the data rate will help. All digital communications require signal levels strong enough to overcome a certain threshold, and it is difficult it will beat analog (SSB) that has no threshold. Actually, there is a threshold on the operator's brain, and makes the difference between a capable, or well trained operator, and the rest of the population. FEC helps, but requires more bandwidth, due to the redundance it adds. Maybe a judicious choice of coding can help, to get as close as possible to the Shannon limit. But there may be a tax on computing power... Codecs can make a difference, the tradeoffs generally are are readability, latency, and tin man tone of voice. Again, many may agree on the good quality ones, but as you sacrifice voice quality, not everyone will be able to copy well. So, it is not a simple matter to lower the threshold, and mantaining wide acceptance on a 2.4 kHz HF channel. YMMV, Jose, CO2JA __________________________________________ XIII Convención Científica de Ingeniería y Arquitectura 28/noviembre al 1/diciembre de 2006 Cujae, Ciudad de la Habana, Cuba http://www.cujae.edu.cu/eventos/convencion Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
