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HD Voice

So how do they sound? Polycom phones have always sounded good, but these two models take things up a notch offering dramatically enhanced sound through Polycom’s  “HD Voice” technologies.

It was long ago decided in the traditional phone system that 3 kHz was the highest frequency required to convey the human voice. This was the defining factor in the sound of a typical phone call. Even as telephony moved into the digital age, everything was built around an 8 kHz digital sampling rate. This again produced an upper frequency limit of around 3 kHz with both the G.711 and G.729 codecs most commonly used in VOIP systems.

HD Voice leverages G.722, one of a family of newer codecs specifically designed to provide broader frequency response without increasing required bandwidth. G.722 supports a sample rate of 14 kHz, delivering audio up to 7 kHz. However, the codec uses advanced data compression so that a call requires only the 64 kbps per call leg (80 kbps with IP overhead), typical of an old-style G.711 encoded call.

Codec selection isn't the only factor involved in HD Voice. The phones themselves are designed around conveying wideband audio. That means better transducers: the microphones, earpieces and speakers. Even the chassis of the phone is significantly enhanced to provide richer, fuller sound without rattles and vibrations.

The difference in sound quality with HD Voice is astonishing and truly must be experienced to be appreciated. Even music-on-hold is more enjoyable; more like listening to the radio. Decide for yourself with this sample of a call over a typical SIP phone and another over an HD Voice connection using an IP650.

Some may ask “why bother?” as business is adequately transacted by phone already. There are many cases where improved intelligibility is beneficial. Consider conducting conference calls internationally with people of profoundly varying accents. Or perhaps consider someone with a mild amount of hearing damage. In both of these cases the additional high-frequency detail truly makes it easier to understand what is being said.

The downside to HD Voice is that both ends of the call must have wideband capable phones and the call must be handled via IP end-to-end. If the call passes over the regular public switched telephone network (PSTN) at any point, then the call will be negotiated down to the more common G.711 codec. Even so, call quality will still be improved, just not as dramatically.

Companies with multiple locations connected via IP can take immediate advantage of the improved quality for inter-office calls. In my case, this was most useful during staff meetings conducted by conference service.


There are numerous methods for provisioning Polycom phones. For a home office or business with only a couple of phones, you can do it right from the phone's LCD display since all the core settings are available. Entering long strings can be a bit tedious, but for just a few phones it works well enough.

You can also set up a phone via a built-in web-based interface (Figure 7), which provides access to all basic settings. This method can be a little frustrating, however, because you need to click a Submit button to save the settings on each screen. Each Submit forces a reboot of the phone, so provisioning via the web interface can be slow.

SIP server web configuration
Click to enlarge image

Figure 7: SIP server web configuration

The alternative, more scalable approach is to use a central provisioning server and have the phone load its firmware and settings from that server at boot time. The phones support a variety of provisioning servers including TFTP, FTP, SFTP, HTTP and HTTPS. The basic network settings must still be defined locally, but just enough to get them on the network and point them to the provisioning server.

Your provisioning server need not be local to the phones. In fact, the phones that I administer, while spread across the US & UK, all load their firmware and settings from a central FTP server. This makes programming the phones and pushing out firmware updates a relatively simple matter, even for a large number of phones.

A set of XML configuration files on the provisioning server define everything about the behavior of the phone. The array of settings exposed is dramatically larger than those found in the web interface. Polycom's provisioning documentation includes a thorough set of examples and detailed explanations of every parameter.

Sometimes being the front-runner in a field has advantages. The long term stability and reliability of Polycom's provisioning scheme has enabled a trend towards the automatic provisioning of its phones with popular IP PBX systems. For typical installations, many businesses will find that the phones can be automatically configured when used with the following systems:

  • Asterisk Business Edition
  • AsteriskNOW
  • Switchvox
  • Digium’s Asterisk Appliances
  • Jazinga
  • Voiceroute’s Druid Unified Communication Server
  • ThirdLane PBX
  • Fonality’s trixbox Pro
  • 3COM Asterisk Solutions
  • TAA’s VDEX-40

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