During early 80s, the bellheads were trying to use wideband codec for voice communication. Those feeble attempts failed along with its benefactor ISDN. Now with the widespread deployment of VoIP, it is more likely use of wideband codec will be routine. But early deployments didn’t use them, because they were more focused on replicating/replacing POTS phone service. Thanks to Skype, more people are aware of the benefits of wideband codec and are exploring incorporating these codecs in their offerings. Two well known examples of this class of codecs are iSAC from Global IP Sound and G.722.2, an ITU standard that will be used in 3G deployments. Both have licensing or patent restrictions. As I was researching this topic, I came across an open and free codec called Speex. This has both narrowband and wideband components and requires comparable bandwidth. From the google search it looks like the quality is quite good. Xten, Asterisk and Open323 (did you now that they also support SIP) all support this codec. I hope that Speex is used more widely by other VoIP service providers. Since Speex is royalty free, media gateway vendors must be able to upgrade their products to support this codec.
The only hitch is I am not sure whether ATA users will observe the added benefit of using a wideband codec.
Posted by aswath at June 18, 2005 12:20 PM
AFAIK, this codec is perfect for voice, but bad for anything alese than voice.
Posted by: rob at June 18, 2005 09:33 PMI don't think ATA users will get anything out of a wideband codec. Although reading the signal power limitations of TIA-968-A gives me a headache, as best I can tell any phone meeting the requirements (which are the technical specs behind FCC Part 68 certification) basically are bandlimited at 4kHz.
Posted by: DG Lewis at June 18, 2005 09:36 PMI believe ATA users may get variable advantage from the use of wideband codecs. Some phones should be capable of passing some frequency components over 4Khz.
It is variable because it depends on the band filter sharpness off the phone as well. For example, a digital cordless phone might be more restrictive in this respect than a low tech plain analog phone plugged to the ATA.
This is unless ATA is using hard line filters for FXS ports as opposed to DSP based digital filtering. If DSP based filtering is used the software can fine tune.
I would like to see some stats using common equipment on the market before scrapping the idea for being stupid.
Posted by: t5amj at June 27, 2005 06:11 PM