[asterisk-users] drop dead fix

[Kevin P. Fleming]

On 10/15/2010 08:59 AM, Danny Nicholas wrote:
> Hello list,
> 
>               I am about to have to dump Asterisk in favor of some other
> VOIP/PBX solution;  the reason?  I have 304 voice prompts recorded as
> 22Khz wav format files that sound like crumpling paper whenever I
> convert them to the 8Khz wav/gsm format required by Asterisk.  I was
> considering trying the G.729 codec, but reading through the specs, I see
> that the 8Khz conversion is going to dump me into the same pile of
> dung.  Any body have any suggestions?

In addition to all the other comments you've received (including the
fact that Asterisk does not "require" GSM format files), keep in mind
that *any* product that plays these files over the PSTN is going to have
to downsample them to 8KHz and, at a minimum, use G.711 companding. That
is what the PSTN uses, so it's not possible to have higher fidelity than
that.

There were some comments in other replies about your files being 'quiet'
(low average volume level)... this won't help your situation at all,
because it means that any artifacts caused by resampling and
compression/decompression will end up at a relatively high amplitude
compared to the original signal (resulting in a low signal-to-noise
ratio), and when the listener increases the volume level on their
listening device, the noise level will be increased along with it. For
these sorts of tasks, you really do want the source material recorded at
a fairly high volume level.

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
skype: kpfleming | jabber: kfleming at digium.com
Check us out at www.digium.com & www.asterisk.org