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Remember hearing FM radio for the first time? Or listening to your first CD after years of scratched Vinyl? That's the experience HD sound brings to a telephone. As voice-over-IP becomes commoditized, the focus of system developers and service providers shifts from providing VoIP to providing higher-quality VoIP.
Taking advantage of the strong marketing behind HDTV, HD-sound is now the accepted brand name for Wideband Voice. This allows service providers to offer superb and pristine audio quality over their IP phone-enabled home gateways. The traditional "narrowband" telephony was a compromise between speech intelligibility and data rates, providing an acoustic bandwidth of 300 Hz to 3.4 kHz. In contrast, HD-sound uses wideband technologies to offer a transmission range of 50 Hz to 7.0 kHz or beyond.
The result is significantly increased intelligibility and a much more natural sound not only for voice conversation, but also for a range of other audio applications, such as MP3 and Internet radio. This article attempts to address the hurdles associated with delivering HD performance in telephony, and explore its market potential.
HD Voice: Wideband Telephony
"Wideband" telephony specifies a transmission range of 150 Hz to 6.3 kHz. While this is not CD bandwidth (20 Hz up to 20 kHz), the increased bandwidth compared to narrowband offers significantly improved intelligibility.
Transmission Spectrum Diagram: In the spectral analysis diagram it is easy to see the larger range in which HD-Sound (bottom) operates. HD-Sound opens up the transmission spectrum to include lower and higher tones than we are used to from narrowband telephony giving the participants a far superior user experience when using Wideband.
Wideband telephony was standardized for ISDN with the G.722 codec about 20 years ago, but never really enjoyed wide deployment. G.722 however did make its way into journalism, where wideband with G.722 is often used for voice transmission from remote locations as an alternative to the poor quality of standard telephones.
As IP-phones already have powerful signal processing capabilities for narrowband speech compression algorithms, wideband codecs can easily be handled by the voice engines within IP-phones. If the analog-to-digital and digital-to-analog converters support a 16-kHz sampling rate, wideband telephony on an IP-phone comes with relatively low additional overhead.Another factor driving the development of wideband telephony is the new DECT standard CAT-iq, which also specifies G.722 as the required codec for HD Voice.
PC soundcards support 8- and 16-, 32-, 44.1- and 48-kHz samplings rates, and generally have the necessary processing power for wideband codecs. PC-based soft-phone applications like Skype already have a huge footprint in the market.
Most enterprise IP-Phones like Siemens' OpenStage series already support wideband. The enterprise market for wideband is an excellent proof of concept as it is much easier to control the hard and software running on the end points. The deployment of HD voice in the residential space is much more difficult. Wideband requires that both parties in a call have wideband capable hardware and that the phone immediately shifts up to the best codec available.
In the past VoIP had to contend with a less than solid reputation. From its early days where only brave pioneers would make a connection over the internet, broadband users have been fast to take up the offerings of new players on the voice service provider market. The traditional trade-off was quality against price.
Today, VoIP quality has improved beyond recognition and is easily comparable to that of POTS services. As available bandwidth and processing power of customer premise equipment becomes the norm, the possibility of using more bandwidth for vastly improved voice quality is very real and imminent. This is where providers can differentiate their services.
Mean Opinion Scores for Narrowband and Wideband codecs: Source - France Telecom. The analysis of the MOS (Mean Opinion Score) values in diagram 2.0 illustrates impressively how wideband is perceived subjectively. Most MOS values for narrowband G.729A come in at around 3.5 whereas HD Voice is perceived to be at least 30% better at 4.5.
VoIP is not just VoIP. HD Sound makes it marketable above and beyond price. A POTS phone call is thin and almost monotone in comparison to a well-implemented HD Sound call. This leads to a "warmer" sounding phone call, where all the nuances of our voice are captured. Mistaking "s" for "f" is now a thing of the past. The possibilities that this brings are manifold. The hurdles associated with bringing it to a wide audience are also considerable.
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