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Andrew Kohlsmith wrote:
<blockquote cite="mid200412170911.46675.akohlsmith-asterisk@benshaw.com"
type="cite">
<pre wrap="">On December 17, 2004 05:49 am, Eric Bart wrote:
</pre>
<blockquote type="cite">
<pre wrap="">I've seen nowhere a plan to improve audio quality.
</pre>
</blockquote>
<pre wrap=""><!---->
Possibly because there's no real need to?
</pre>
<blockquote type="cite">
<pre wrap="">It seems that the Skype success is partly due to its
16 KHz audio bandwidth. It gives users the feeling that
the far party is in the same room.
</pre>
</blockquote>
<pre wrap=""><!---->
I've never heard any complaints about regular telephone quality, and that's
8-bit 8kHz (64kbps). Are you sure that this is something that really needs
consideration over perhaps working out a way to get packet loss concealment
into *?
</pre>
</blockquote>
OK, now here's my 2c:<br>
<br>
1) if you have less than perfect connectivity, PLC and a good
jitterbuffer will help more than using a wideband codec. I'm working
on this, and have an implementation of this in iaxclient-cvs. Once
it's worked out there, we can port this stuff over into asterisk proper.<br>
<br>
One thing I could use help with is coding the actual interpolation
algorithm for codecs which don't natively support this (i.e. for GSM,
G711, PCM, etc). I don't know if G.711 Appendix 1 is patented or not
(probably not), but someone could probably implement that relatively
easily (there is sample code, but unfortunately, it has copyright).
See <br>
<a class="moz-txt-link-freetext" href="http://www.fokus.gmd.de/research/cc/glone/employees/henning.sanneck/resource/doc/av/9A170124.pdf">http://www.fokus.gmd.de/research/cc/glone/employees/henning.sanneck/resource/doc/av/9A170124.pdf</a><br>
<br>
I think I might plug in the sample code just to see how well it sounds
(and not distribute this, of course).<br>
<br>
2) Wideband in asterisk _could_ be implemented solely as a different
_set_ of codecs. There's a couple of issues:<br>
<br>
a) The codec "space" in asterisk is limited to 15 voice codecs, and
these types are all used already, I think. We'd probably want to
have support for wideband versions of PCM, uLaw, aLaw, speex, and maybe
others..<br>
<br>
b) Presently, "samples" is used in asterisk frames: If the wideband
codec uses a sampling rate that is a multiple of 8khz (like 16khz), we
could just set this parameter to be the number of 8khz-equivalent
samples in the frame, otherwise the implicit equivalence of 8samples ==
1ms is broken. A 44.1khz codec, though, wouldn't fit this paradigm.<br>
<br>
-SteveK<br>
<br>
<br>
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