[asterisk-users] MagicJack quality

[Steve Underwood]

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