[Asterisk-Users] Audio quality

[Robert Keller]

Scott, I have been using xten's eyebeam and a jabra bluetooth headset with
pretty good results. The local calls to PC's and out an analog line have
been good.

I have *@home 1.0 with a clone X100P card.

Robert

> From: Scott Lamb <slamb at slamb.org>
> Reply-To: Asterisk Users Mailing List - Non-Commercial Discussion
> <asterisk-users at lists.digium.com>
> Date: Fri, 13 May 2005 17:36:00 -0700
> To: asterisk-users at lists.digium.com
> Subject: [Asterisk-Users] Audio quality
> 
> I'm a new Asterisk user. I've managed to set it up to do everything I
> want except sound good. Currently, Asterisk sounds considerably worse
> than my cell phone. I know VOIP can be _better_ than my cell phone,
> because I've heard Skype do it. (Using 32k iLBC, I believe.)
> 
> I did an experiment with audio quality:
> 
> 1) I made a recording which was pretty good. I used an iSight
> microphone and recorded at its native 48k sampling rate in Audacity.
> Then I trimmed it and ran their noise reduction filter.
> 
> 2) I transformed it into a bunch of other formats with this script:
> 
>    for base in "$@"; do
>        for rate in 8000 16000 32000; do
>            sox "$base"-48000.wav -r $rate "$base"-$rate.wav
> resample -ql
>            speexenc --vad --dtx --rate $rate "$base"-$rate.wav
> "$base"-$rate.spx
>            speexdec "$base"-$rate.spx "$base"-$rate-fromspx.wav
>        done
>        sox "$base"-8000.wav "$base"-8000.gsm
>    done
> 
> 3) I listened to them all with Quicktime Player.
> 
> From that I determined that a WAV with 32k sampling rate sounds good
> to me, but I'm not happy with 8k or 16k. Since adding lossy
> compression is only going to make things worse, that rules out most
> of Asterisk's codecs.
> 
> The 32k (ultra-wideband) speex with default settings sounds good, and
> it's a free codec. I'm not real concerned about bandwidth use, but it
> does pretty well there, too.
> 
> I understand that Skype uses ultra-wideband iLBC; it's audio quality
> is also good. But I understand there are patent problems. (Are
> licenses even available? How much do they cost?)
> 
> I've got three problems for actually using this though:
> 
> 1) Can asterisk load 32k audio files? I see that the current CVS's
> format_wav.c can not. Is there another module that does? I might try
> modifying the WAV loader. Are there assumptions of 8k throughout
> Asterisk, or is this pretty isolated to that file?
> 
> 2) Are there higher quality versions of the Asterisk sounds? They're
> in a nice, professional voice, but 8K GSM just sounds awful. If the
> source encodings are available, I could resample them into whatever
> else in a similar fashion to what I've done above.
> 
> 3) Are there clients that support the 32k sampling rate?
> 
> a) I'm particularly interested in softphones for OS X. The ones I see
> are X-Lite, SJphone, and iaxComm. X-Lite has some weird distortion
> problems for me with even 8k ulaw (<http://support.xten.net/
> viewtopic.php?t=3626>). SJphone's Speex support is weird - they have
> 8.0k and 15.2 k (?). iaxComm has the settings I want, but they sound
> awful. I'm not giving it a fair test, though; see #1.
> 
> (None of these have a decent user interface either, but one problem
> at a time...)
> 
> b) Any hardware phones?
> 
> Regards,
> Scott
> 
> -- 
> Scott Lamb <http://www.slamb.org/>
> 
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