This article originally appeared in the Sept. 2010 issue of INTERNET TELEPHONY

Public discussion of HD voice has been high on opinion and low on hard evidence. But earlier this year Skype (News - Alert), which has the biggest wideband-enabled voice network in the world, released some real-world numbers showing that phone calls last longer when the sound quality is better.

The numbers are based on hundreds of thousands of Skype calls made between November 2009 and January 2010, both voice only and video calls. The experiment recorded the duration of the call, the codec, the available bandwidth, and the caller's opinion of the sound quality on a scale of zero to five. The sound quality opinion was gathered by a pop-up question after the call. Since this is Skype, and the majority of the calls were video calls, I assume the calls were mainly personal.

The lowest quality calls used the G.729 codec, and the highest quality calls used the super wideband mode of Skype's SILK codec.

The big takeaway is that there is a roughly linear relationship between perceived audio quality and length of call, ranging from an average of 22 minutes at an average sound quality of 3.4, up to 31 minutes at a sound quality of 3.9.

This is a huge difference, and the size of the sample makes the result practically incontrovertible. For service providers that bill by the minute, improving sound quality would lead directly to higher revenues. This may be part of the motivation behind Orange's (News - Alert) move to deploy wideband audio on its wireless networks.

But for subscribers the lessons are a little more subtle. Is it better to spend more time on the phone? On a business call you don't want to waste time, so one might think it desirable to aim for a shorter call. I hypothesize that the calls are longer because higher quality audio is less fatiguing. Audio processing takes massive computational power. When one is trying to follow a poorly-audible conversation it taxes those unconscious parts of the brain that do audio processing. If this is so, then there is a clear benefit to HD voice on business calls: better comprehension and less fatigue will lead to better results and perhaps less time wasted on the phone.

Michael Stanford (News - Alert) has been an entrepreneur and strategist in VoIP for more than a decade. (Visit his blog at www.wirevolution.com )