[Asterisk-Users] Correction: Asterisk sound files, audio bandwidth, and sound quality

[Sherwood McGowan]

I have to barge in here...

Guys, the reason the audio sounds like hell is most probably for mulitple
reasons. First, what codec is the prompt encoded? Next, what codec is the
client using? If you're using, for example SIP clients with G711u, asterisk
has to re-encode (on the fly I might add) the prompts to ulaw format to be
usable to that client. Only on GSM based clients would the audio sound
mildly like the actual file. Also, what's the current load, memory, how many
calls are running on the server, how many calls on hold listening to that
music? If you're not encoding only one format for those calls, guess what,
you're incurring load to re-encode to each format in use on the fly. 

I am a music producer, have been for several years. One of the things I do
on the side from my day job as a VOIP Admin/Engineer is make prompts and
music for customer's PBXs. I typically make a WAV file, and then do my
filtering, compressing, and finally normalizing, then save it. Finally, I
put the files in the server in question and use sox to re-encode multiple
formats: gsm, ulaw, alaw, etc.... You'll find the results are much better
than just allowing Asterisk to re-encode on the fly since it's busy handling
the rest of the system as well. Another way to help it is to only allow one
codec.

Sorry, but no one had hit on this yet. 

Cheers
SKM

->-----Original Message-----
->From: asterisk-users-bounces at lists.digium.com 
->[mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of 
->Stephen Bosch
->Sent: Wednesday, September 28, 2005 6:26 PM
->To: Asterisk Users Mailing List - Non-Commercial Discussion
->Subject: Re: [Asterisk-Users] Correction: Asterisk sound 
->files, audio bandwidth,and sound quality
->
->Kevin P. Fleming wrote:
->> Stephen Bosch wrote:
->> 
->>> When I listen to the GSM compressed prompts, I can hear 
->subtle noise 
->>> when the person is speaking -- this is irrespective of whether I 
->>> listen to the prompts through the TDM-400 on an analogue phone or 
->>> whether I do so directly on a workstation. It has to be 
->possible to 
->>> do better than that.
->> 
->> You are referring to the prompts distributed with Asterisk? Those 
->> sound perfectly clear to me, and to everyone else I know 
->who has heard them.
->> They were professionally recorded in a studio and then converted to 
->> GSM format, which does not introduce noise.
->
->Recording them professionally in a studio is the right way to 
->do it, of course -- but that's probably not where the problem lies.
->
->They sound noisy to me. First, the amplitude is low. When I 
->increase the gain in my sound card mixer, there is definitely 
->audible noise (it's a subtle static). I've sent the files to 
->others to play back on different equipment, and they tell me 
->they hear the noise too. I don't think I'm hearing things.
->
->Right now, in our business, we've got voice mail provided by 
->our telco (Telus). The Telus prompts come in much clearer 
->than the Asterisk prompts. We've asked a couple of 
->independent third parties to evaluate Asterisk and the Telus 
->prompts in comparison, and so far every person has noted the 
->noise on the Asterisk prompts.
->
->If we want to sell systems running Asterisk, that's going to 
->be a tough one to get past, especially in these parts.
->
->Perhaps it's the way the files are compressed?
->
->-Stephen-
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