[Asterisk-Users] SPA-3000 and quiet voicemail

[Rich Adamson]

> I have a Sipura SPA-3000 for access to my standard analog PSTN line.  I
> have the SPA-3000 answering and then directing all calls into Asterisk.
> 
> This setup is working fine for everything except voicemail.  Most, about
> 2/3 or so, of messages left come across very quiet when the voicemail is
> played back.  A regular conversation with these people, regardless of
> the phone used on my end, works just fine.
> 
> I did some googling and came up with two links of similar problems, but
> only for people that are using Zaptel cards:
> 
> http://lists.digium.com/pipermail/asterisk-users/2005-March/096485.html
> http://bugs.digium.com/bug_view_page.php?bug_id=0002023
> 
> I can't figure out what is going on with the SPA-3000 setup I've got,
> and it's really odd that everything except voicemail works perfectly.
> 
> Suggestions would be most welcome.

Best guess is that your issue is unrelated to bug 2023. But, the only
way to prove that is to use a transmission test set to send a tone of
a known level through the spa3k to voicemail and then use the test set
to measure the playback. Take a look at bug 2022 on how that was done 
(2022 and 2023 are directly related).

You might find http://www.routers.com/asteriskprob/asterisk-config.htm
to be usefull as well.

The audio level to/from your spa is highly dependent on how far away
from the telco's central office you are located. For example, if
you're 15,000 feet away (length of the telco's cables, not the point-
to-point distance), the cable loss will be about 6db. The further
away you are, the larger the loss.

It would be very interesting to know exactly what that cable loss
happens to be in your case. It also can be measured by accessing
your telco's milliwatt generator from your location (see the url
noted above).

If you can determine that loss, then point your browser to the spa's
"pstn line" page, and near the bottom change the "spa to pstn gain"
and "pstn to spa gain" to higher values. You might try increasing
those values by +3db at a time, save and reboot the spa, and test
the result using an ordinary analog phone. Changing the values to
high will likely result in some amount of echo, and possibly enough
distortion to dtmf tones to make the spa unusable, callerid to fail,
etc.

There seems to be at least some opinion the voicemail audio level
problem might be related to exactly which codecs and voicemail
recording format is being used. In very general terms, the g711
(phone/spa) to gsm (vm format) has a greater audio level loss then
does g711 to wav format (as one example only).

If you have configured your spa pstn -> asterisk to use g729, then
try changing it back to g711 to see what impact that might have.

Saying the above in a reverse sense, leaving a voicemail via a
sip phone verses an spa3k (w/g711) is exactly the same audio levels.
The only variable left is the spa3k -> telco loss (and spa3k level
settings).