High definition (HD) is the big trend in electronics these days: We have HD TVs and HD DVDs, and now we’re hearing about HD VoIP. When it comes to telephony, what does HD really mean, what’s it going to cost, and who really needs it? I set out to find answers to these questions after reading an article about HD VoIP in a recent issue of the Wall Street Journal. Here’s what I found out.
What’s the point?
Just as HD video gives you clearer, sharper pictures on the screen, HD voice technology provides you with clearer, sharper sound quality on your phone. It’s a little like the difference between listening to a standard, factory-installed car stereo system or a high-dollar custom system with eight speakers and a subwoofer. The former works just fine, but the second makes for a significantly richer and fuller sound experience.
How do they do it?
So what makes VoIP high-definition? A big part of the difference lies in the codecs. Also called a voice encoder, a VoIP codec is a program that converts analog sound waves into digital data.
Most also use compression and decompression to make it possible to transmit voice across the IP network with less bandwidth. But in this case, codec stands for coder-decoder, rather than compressor-decompressor.
Common voice codecs include G.711, G.729A, and G.723.1. These numbers refer to International Telecommunications Union (ITU) standards. However, there are others based on non-ITU standards, such as LPC10 based on a U.S. government standard and GSM, the same encoding used by GSM mobile phones.
HD VoIP transmissions use wideband codecs, which sample a much wider range of audio frequencies. For instance, Polycom HD VoIP phones sample between 150 Hz and 7,000 Hz, in comparison to the 300 Hz to 3,400 Hz that’s typical of the original VoIP codecs such as G.711. An example of a wideband codec is G.722.
Why does it matter?
Why does this extended range matter? It matters because human voices are capable of a broad range of frequencies (somewhere around 100 Hz to 8,000 Hz or more). That means HD VoIP phones can more accurately produce sound that’s in keeping with human speech. That in turn makes it easier for you to understand the speaker on the other end, especially for voices in the extreme low or high end or when someone is speaking with an accent that’s difficult to understand.
Who has it?
Polycom is responsible for one of the first HD VoIP phones. The company unveiled the SoundPoint IP 650 a little more than a year ago in September 2006.
Texas Instruments is another company that’s working on HD VoIP technologies. In April, the company licensed a “super wideband codec” from a German company and published its “A Vision for Voice” white paper.
What does it cost?
The Polycom IP 650 debuted with a suggested retail price of $499, and it can handle up to six lines. (You can find it now for under $300.) You can turn the desktop phone into an attendant console by adding up to three expansion modules that make it able to handle 12 lines and up to 24 simultaneous calls. It supports Microsoft Live Communications Server and works with Office Communicator. It also has a USB port so you can add more applications in the future.
This may sound like more phone than you need — or want to pay for. However, at the present time, HD VoIP is still more of a luxury item than a necessity. Only higher end phones support it, and they also come with additional extra features.
What’s the catch?
Other than cost, what are the drawbacks to HD VoIP? One problem is that you may lose all that high quality when you call someone outside the corporate network. That’s because the PSTN resamples calls that go through its network, and that typically means lower quality. Since calls between different service providers often go through the PSTN, this could apply to many or most of your calls.
What about compatibility?
The good news is that HD VoIP will work with the popular open source Asterisk IP PBX. You may, however, have to make some tweaks to get it to work correctly. This involves some simple editing of the sip.conf file, a task that’s not too daunting for the average Asterisk administrator.
You may encounter compatibility issues, though, when trying to place calls to non-HD devices that use G.711 with the current version of Asterisk (1.4). But Asterisk plans to fix this in future versions. (For more info on testing Asterisk with G.722, check out this eWeek.com article.)
What’s it good for?
In addition to the best sound quality possible, HD VoIP can offer other benefits. For example, it could make it much easier to use voice recognition technology over the phone and cut down on inaccuracies that currently plague such systems. (I’ve spent many frustrating minutes repeating myself to automated systems that were unable to understand my Texas accent; anything that could improve on that type of experience would be something I’d welcome.)
One of the initial disadvantages of VoIP was the call quality. Now that reliability has greatly improved, companies can concentrate on making the sound clearer and cleaner. One way of doing that is by extending the frequency range using high-definition technologies that depend on wideband codecs.
HD VoIP is still in its infancy, and only a few vendors are making equipment to support it. But you can look for that to change as users demand better quality and as vendors overcome technical limitations, such as the downgrading of voice quality when calls go through the PSTN.
Deb Shinder is a technology consultant, trainer, and writer who has authored a number of books on computer operating systems, networking, and security. She currently specializes in security issues and Microsoft products, and she has received Microsoft’s Most Valuable Professional (MVP) status in Windows Server Security.
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