[asterisk-users] MagicJack quality

[Tzafrir Cohen]

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?

Anyway, the ProSLIC chip does not seem to support it. 

-- 
               Tzafrir Cohen
icq#16849755              jabber:tzafrir.cohen at xorcom.com
+972-50-7952406           mailto:tzafrir.cohen at xorcom.com
http://www.xorcom.com  iax:guest at local.xorcom.com/tzafrir