Tzafrir Cohen wrote: > On Sat, Jul 12, 2008 at 10:26:24AM +0800, Steve Underwood wrote: > >> C. Savinovich wrote: >> >>> I am puzzled by the quality of magicjack. I keep trying to figure out how >>> they can the quality be that adequate. Since Skype also has an excellent >>> quality, that leaves me to believe that software based calls (softphones) >>> could have and advantage over hardphones, provided there is a parameter that >>> those 2 companies are addressing. >>> >>> Anyone's thoughts on this? >>> >>> CS >>> >>> >> I don't know what Magic-jack does (I've never actually seen one), but I >> know the key thing about Skype that impresses people - its wideband >> voice codec. A lot of people poo-poo the idea that wideband voice has >> value in a phone call. They are either close to deaf, or have never >> tried it. Clarity is profoundly improved. Skype seems to use various >> tricks to keep the packet flow smooth, but its wideband that makes it >> sound better than the PSTN. >> >> You might think a standard phone plugged into an adaptor, like a >> Magic-jack, would be limited to narrow band voice, as that is all the >> phone was designed for. It turns out most phones only aggressively >> filter at the low end of the band. They let a lot of energy above 4kHz >> through, and they do generally sound better through a wideband codec. >> >> Many modern line interface chips are actually capable of running in a >> 16k samples/second mode, even though most are programmed for 8k >> samples/second. I think the ones on the TDM400P type cards can. Some >> from Silicon Labs certainly can, and chips from Zarlink and others can. >> > > The DAA in those cards can work in 16Hz. So they can send higher quality > samples to the telco. Provided Zaptel supports it. But then again, it > will get lost as soon as it gets converted to digital at the telco, > right? > I guess I wasn't clear. What I said was only useful for a SLIC to phone connection. It won't be of any benefit for a DAA to PSTN exchange connection, for the reason you state. > Anyway, the ProSLIC chip does not seem to support it. > Silicon Labs make a Wideband ProSLIC, Si 3216, which is, er, wideband. As I said before, Zarlink and other make them too.
Regards, Steve _______________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- AstriCon 2008 - September 22 - 25 Phoenix, Arizona Register Now: http://www.astricon.net asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
