[Asterisk-Users] Prompts and sound quality of the X100P card (FXO card)

[Steven Critchfield]

On Wed, 2003-09-10 at 10:15, Lee Goodman wrote:
> Hi
> 
> We are trying to get better sound quality out of the prompts on our Asterisk
> system. We had some new ones made by thevoice.digium.com and they are in WAV
> format instead of the default GSM format on the Asterisk server. The problem
> is, when you dial in to the server using the FXO card (X100P) you really
> can't tell the difference between the WAV prompt and the GSM prompt,
> however, if you listen to the prompts via a SIP phone you can hear a clear
> difference. Is the FXO card compressing the WAV file? Is there anyway to
> tweak the FXO card to make it sound better?

Via SIP you are only doing 1 D/A conversion, and it is closest to the
speaker. At worst on the SIP connection, the only change to the prompt
is a codec change and that is unlikely.

Via X100P, You have a D/A conversion to get it on the line, then at the
phone switch it is digitized and dropped off at the appropriate port to
go out to whatever phone you are using where there is another D/A
conversion then it goes to your phone. If it is a cell phone, then there
is compression on the cell link before it gets to you and the D/A
happens in the phone itself. Not to mention the probability of a mile or
more of analog copper in the link.

So this isn't necessarily a problem with the X100P but in the underlying
technology. If you like, I could make a phone number available for you
to hear your prompts played over a PRI connection so you can see that it
is just an analog problem.
-- 
Steven Critchfield  <critch at basesys.com>