[Asterisk-Dev] 16 KHz audio ?

[Steve Underwood]

Eric Bart wrote:

>>>Please read this skype experience:
>>>http://www.vonage-forum.com/article312.html
>>>
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>>>
>>Isn't marketing material wonderful? :-)
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>Oops. Is Vonage now selling Skype ?
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>Whatever. I've tested Skype. I'm telling it's HiFi !!!
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>>>Skype may be using a 24 KHz bandwidth. I know that they're also using
>>>a very good compression codec. 
>>>      
>>>
>>I think 24kbps is rather more likely than 24kHz bandwidth :-)
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>No. I read in a forum that someone saw that Skype was opening a sound card 
>driver at 48KHz. Why would it if not for using it ?
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They do that because few sound cards can sample at 16k/second. They use 
48k/second and rate convert in software. The codec isn't using 24kHz 
bandwidth.

>It's not because you're sampling at 48K that you'll get a huge output rate.
>It depends on the codec efficiency.
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Duh! yeah!

>>Skype uses iLBC. 
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>It's using some globalipsound technology.
>http://www.globalipsound.com/customers_partners/customers_partners.php
>http://www.globalipsound.com/solutions/solutions_Codecs.php
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That's iLBC

>>I think the wideband version of iLBC is 24kbps.
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>On my PC I have 4 DivX audio codecs for 44KHz : 32, 22, 20 and 16 Kbps
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Many things are possible, with variably crappy results. Actually, it 
doesn't take many extra bits to code the higher frequencies. The bulk of 
the bits concentrate on the first 4kHz.

>I'm sure it's possible to get a streaming 24KHz bdwdth in 24kbps. However 
>maybe it's not available for a gnu software.
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The wideband iLBC isn't available for royalty free use, as far as I 
know. They only allow the narrowband to be used in that way.

Regards,
Steve