On 01/06/2011 05:25 AM, Tim Panton wrote:
On 5 Jan 2011, at 13:07, Steve Underwood wrote:

G.722.1 is a 7kHz bandwidth codec. G.722.1C is a stretched version offering 
14kHz bandwidth. These are most often found in Polycom phones, but they are 
available elsewhere. The only widely supported HD codec is G.722. Pretty much 
anything offering wideband voice supports G.722.
Except skype which only supports SiLK as the HD codec. I mention this because 
most people's experience with HD will be in a Skype-to-skype call,
although admittedly not in this group.
That's a very good point, although Skype does support more codecs than just Silk, and I believe G.722 may be one of them. Nonetheless, it is Silk that people have got used to. It offers about 11kHz bandwidth, so it is wider band than G.722. The critical addition than wideband gives over normal telephony is the 5kHz to 7kHz area, where a lot of the energy that allows us to differentiate the unvoiced phoneme lies. The energy between 7kHz to 15kHz does, however, add a lot to the human voice, and allows for a more relaxed listening experience - its just less tiring to listen to.

Steve


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