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. > > If Magic-jack sounds impressively clear, a wideband codec would be my guess. > > Regards, > Steve > > Like I said, Speex. It features Narrowband (8 kHz), wideband (16 kHz), and ultra-wideband (32 kHz) compression in the same bitstream.
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