[asterisk-dev] iLBC packet loss concealment

[Rich Adamson]

Matt Ranney wrote:
> On Apr 16, 2006, at 6:33 AM, Steve Underwood wrote:
> 
>> Skype is certainly better than the PSTN when going Skype to Skype, but 
>> why do people think it sounds better than the PSTN when going to the 
>> PSTN? Is it just psycological, or are they using an environment (e.g. 
>> headset) that just sounds better than their usual phone? Having they 
>> been using a Cisco 7940 with G.729, where a real PSTN to PSTN 
>> connection would sounds rather better? I find it an interesting 
>> comment that Matt made.
> 
> Part of it I'm pretty sure is that headsets just sound better than 
> handsets in most cases.  Part of it could also be that Skype/ilbc 
> wideband sounds better than g.729.

In addition to all of the factors previously mentioned (eg, audio 
bandwidth, codec, etc), other pstn items impacting perceived audio 
quality include:
- the characteristics of the analog phone itself (some are very poor),
- noise (and induction) on the pstn line,
- quality of the plant (eg, copper cables),
- low audio levels due to lengthy pstn lines, etc,
- audio bandwidth restrictions built into remote line concentrators,
- etc, etc.

A non-technical pstn user only knows that using Skype (or any other pstn 
alternative) sounds louder and clearer, but doesn't have a clue why.