The PhoneBoy Blog


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HD VoIP? Oh, Brother…

VoIPGirl is asking a question about whether or not people should consider HD VoIP when they are choosing a VoIP service. I’ve never heard anyone advertise that, so it’s not like a consumer would even know how to look for it. Meanwhile, I will attempt to answer her question.

Without getting too technical here, when a VoIP call is initiated, it is possible to utilize one of a number of codecs. The ‘Co’ means compression, the ‘dec’ means decompression. More succinctly, it is the method by which your analog voice is compressed and sent across the wire as ones and zeros. The codec used will often depend on the available bandwidth and endpoint capabilities.

Let’s use Skype as an example. When you make a Skype-to-Skype call, the call quality is wonderful. Why? They use something called ISAC (warning: PDF link), which is a proprietary codec by Global IP Sound. It is a “wideband” codec that sounds pretty damn good. When you make a SkypeOut (PSTN) call, however, the codec used is G729, which is a narrowband codec that doesn’t sound quite as good.

Presumably, if you are using a service that supports “HD” VoIP, then the “HD” codec, whatever it is, will only come into play on-net, meaning within the relevant VoIP provider’s network. Once it goes off-net (e.g. to the PSTN), a different codec will be used (G711 or G729). This is all done on the fly and completely transparently to the end user, except for the obvious sound quality difference.

Should a consumer care about HD VoIP? Unless you call people within the same provider a lot, it’s not going to matter. It won’t hurt anything, but it won’t help either.


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