[asterisk-users] Poor VoIP voice quality in one direction from three providers

[John A. Sullivan III]

On Thu, 2009-10-22 at 16:04 -0700, Robert L Mathews wrote:
> We currently use asterisk 1.4.x with two Zaptel cards connected to POTS 
> lines. So we make "outbound" calls from their softphones (using ulaw 
> format), which go over a dedicated DSL line to the asterisk server in 
> our office, which then converts the calls to POTS.
> 
> This all works fine, assuming there aren't any unusual problems. It 
> sounds as good as POTS on both ends.
> 
> However, we don't want to maintain the DSL line or deal with the hassles 
> of analog/digital conversion any more. So we want to switch to a 
> reliable VoIP provider and move the asterisk server to one of our 
> colocation data centers.
> 
> We've tried getting test accounts with three VoIP providers: FlowRoute, 
> CallCentric, and Vitelity. In our tests, outbound calls now go from 
> softphones -> asterisk -> VoIP provider -> outside world. We use ulaw 
> all the way through.
> 
> But with all three providers, we see a curious thing: The audio quality 
> in the direction from our softphones to the outside world still sounds 
> as good as POTS, but the audio quality in the inbound direction (outside 
> world -> VoIP Provider -> asterisk -> softphone) is noticeably worse. It 
> sounds "overcompressed" or "slightly robotic" somehow, with a decrease 
> in dynamic range. It's not lagged or echoey; it just sounds like it's 
> maybe using a crappier codec than ulaw, in that direction only.
> 
> I'm baffled by this. Both legs of the calls show as "Format: 
>       0x4 (ulaw)" in "sip show channel". Testing the first provider, I 
> just assumed that their analog->digital conversion was inferior to what 
> the Zaptel cards offer (i.e., that they were injecting inferior sound 
> quality into their ulaw connection)... but we're getting exactly the 
> same results with all three providers, which makes me think it's us.
> 
> Why might this happen? Is there any possible reason other than "all 
> three of the VoIP providers are decreasing the audio quality before 
> injecting it into the ulaw stream"?
> 
I don't know if it is the same issue but we had just the reverse problem
and only with softphones.  The inbound quality from Vitelity was
excellent but the outbound was horrible.  After beating on the problem
for weeks, tweaking all aspects of both the network (packet
prioritization) and kernel (process prioritization), we achieved only
marginal improvement.  It finally turned out to be the headsets.  We had
bought mid-range Logitech headsets (actually the most expensive ones
from our local retailer).  Once we swapped them out for Plantronics
Audio 655 headsets, the problems went away - John
-- 
John A. Sullivan III
Open Source Development Corporation
+1 207-985-7880
jsullivan at opensourcedevel.com

http://www.spiritualoutreach.com
Making Christianity intelligible to secular society