[asterisk-users] MagicJack quality

[Steve Underwood]

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