Get ready for high-def voice

It will be years before it's pervasive, but preparing now will help

High-definition voice -- a rarity in today's business networks -- is becoming more common, so it makes sense for corporate telephony executives to figure out now how they will make the transition, experts say.

If they want to, IP PBX vendors can issue software upgrades to support better-quality voice calls, but upgrading handsets and getting service providers onboard with the technology is a more complex proposition that needs to be thought through, they say.

The benefits of HD or wideband voice include an easier understanding of what is being said and a more authentic reproduction of live speech, both of which are essential in immersive telepresence systems that generate the illusion that conference participants are seated across from each other in the same room, says Jerry Knight, CTO of Accessline, the audio services arm of video service provider Telanetix.

Diagram of an HD voice network

"Video perhaps is not as important as audio in creating that impression," Knight says. "Audio is at least as important."

The benefits of HD are not so obvious in voice-only uses. But the difference can be significant especially with speaker phones and when talking to people with strong accents, where every bit of clarity helps, says Polycom co-founder and CTO of its voice communication branch Jeff Rodman. "In these cases we need all the clues we can get," he says.

HD voice gives better quality than what used to be the premier telephony standard in the public-switched telephone network (PSTN) -- toll-quality voice.

HD voice generates frequencies at the high end of human speech that toll-quality voice cuts off. In practical terms this means being able to hear the difference between words like "pig" and "fig" without asking whether that's a p as in Peter or an f as in Frankenstein.

Wideband voice pushes up the top frequency range covered by the voice coder-decoders (codec) from about 4 kHz to something higher, typically 7 kHz, but it can go even higher to 14 kHz or 20 kHz. One consequence of this wider band is the need to sample speech more times per second in order to capture more of its subtleties. Rather than 8,000 times per second, sampling jumps to 48,000 times per second.

That means the VoIP phones supporting HD need more powerful processing and memory, both of which cost more, but with Moore's Law applied to the phones, the cost differential is narrowing. For example, Polycom's SoundPoint IP 501 phone with Power over Ethernet (PoE) and three lines but with no wideband support costs $295. A roughly comparable SoundPoint IP 550 with PoE, four lines and HD support costs $369.

As Polycom introduces HD phone models, it is phasing out the equivalent narrowband phone, so eventually all its line will support wideband and remain backward compatible with narrowband, Rodman says.

Because the endpoints and the networks between the endpoints must both support HD voice in order for it to work, most wideband deployments are within corporations, not between them, says William Bumbernick, CEO of Alteva, hosted VoIP provider. "The ability to call a different company on a different carrier and completing an HD call is becoming more and more expected," he says, but "today, the chances are still pretty slim that that will happen."

If wideband voice is to become a reality, carriers must invest in upgrades to their VoIP networks, and that could take five to 10 years, Knight says, although Rodman is more optimistic, estimating three to five years. To establish HD VoIP calls using SIP, networks must have the intelligence to negotiate the use of HD codecs.

Despite its advantages, HD voice is not for everybody. Companies that have recently invested in narrowband VoIP systems may want to wait until their next upgrade cycle, Bumbernick says. And if they are just moving to VoIP but have doubts about whether their IP networks will support it, they should invest in network upgrades first and foremost, he says.

But for companies that already have VoIP and are looking to refresh their gear, HD may be a wise investment, he says. If the new voice system is slated for an eight- to 10-year life, it makes sense to have it HD-capable. "You're best served to choose technology that will get you as far down that eight-to10-year path as possible," he says.

Once the IP PBX supports HD, companies can upgrade their handsets incrementally to support wideband, he says. Key executives, for example, that would benefit from clearer calls could get the more expensive HD phones now, while others keep narrowband handsets.

Adhering to HD codec standards is essential if businesses hope to share the improved experience with partners they talk to. There are several, such as G.722, G.722.1 and G.722.2 all of which produce wideband voice but require different amounts of network bandwidth to send their encoded signals -- 64Kbps, 24Kbps and 10Kbps, respectively.

Similarly, the three codecs require differing amounts of processing power -- 14 MIPS, 5.5 MIPS and 38 MIPS. So there are trade-offs that vendors have to weigh in making their selections.

And there are trade-offs that customers have to make as well, says Knight. "Except for specific environments where the need is clear, you would put HD voice in the category of a luxury," he says. "But if the choice is between systems that are equivalent in cost, then an HD option is something that's nice to have."

Learn more about this topic

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Copyright © 2009 IDG Communications, Inc.

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