What Is HD Voice?
HD Voice, or wideband audio, as it is also known, refers to the next-generation of voice quality for telephony audio resulting in high definition voice quality compared to standard digital telephony "toll quality." HD Voice uses wideband codecs (such as G.722 and G.722.2) audio connections to more accurately reproduce the human voice with a wider range of frequency coverage. The result is significantly more natural sounding speech and a wider range of sounds promoting audio clarity and clear conversation.
HD Voice is a significant step in the evolution of audio clarity and quality for telephony systems, one which can lead to greater customer satisfaction. In comparison between HD Voice and traditional telephony audio, many people can distinctly hear a difference and the general sentiment is that HD Voice provides more of a feeling of "being in the same room" with the person on the other end of the phone line.
HD Voice Market Trends
Support for HD Voice has grown rapidly as part of the transition from TDM to IP communications. Specifically, VoIP service providers have been able to support HD Voice capabilities for some time, initially most using their own proprietary codecs. This is changing as these codecs are becoming more available in terms of licensing, and standards-based codecs are becoming more prevalent.
Equipment manufacturers have been able to incorporate HD Voice into telephone sets and into their IP PBXs for some time, but only now with the service providers supporting them can enterprises take advantage of this functionality.
Service providers are increasingly supporting HD Voice for both fixed and wireless. This provides them with advantages in terms of better communications between users of the network, and will increasingly pressure other providers to follow suit or to lose customers to competitors who can provide a better voice quality service. Orange, the first provider to support HD Voice in a wireless environment when it rolled it out in Moldova, has its HD Voice-capable network in France, and is currently trialing HD Voice in the UK.
However, most deployments up to this time have been on particular networks, creating "islands" of HD Voice capability. Efforts such as the Xconnect High-Definition Voice Peering Federation enable operators to work on getting the necessary interoperability to start to break down the islands.
One Issue being addressed is trancoding from one HD Voice codec to another where different codecs are being used, particularly between fixed line and mobile environments, and between which the G.722 and G.722.2 standards are prevalent. The following figure is an example of HD Voice communications between a fixed line enterprise and a mobile user.
Benefits of HD Voice
HD Voice delivers higher quality voice transmissions by extending the frequency of range of traditional or narrowband voice calls (300 Hz to 3400 Hz) out to wideband audio ranges (50 Hz to 7000 Hz).
This creates a better overall experience for users because on the phone it:
- Makes it easier to recognize voices
- Makes it easier to distinguish the sounds of fricatives, such as s, z, and f
- Fades or cuts out background noise
- Provides more natural sounding speech
The improved quality also encourages longer call durations, and especially delivers a richer presence for conference calls and improves comprehension with people of different accents. In terms of automation, HD Voice provides a more accurate environment for voice recognition and speech detection.
HD Voice Technology
Codecs
To use wideband audio, voice data is coded differently than for narrowband audio, which means a move away from codecs such as G.711. Many wideband audio codecs are in use today, with most aimed at a different type of connectivity and vying to become the "de-facto standard" codec for specific applications.
The following figure shows the amplitude versus frequency for a 30 second sample of audio. It depicts the differences between wideband audio and the G.711 narrowband audio frequency ranges, demonstrating the level of extra information the wideband signal can depict.
Some wideband codecs are proprietary and others are standards-based. Some proprietary codecs, including Skype’s SILK, have been made available and/or been licensed royalty-free, enabling a broader field of application, and creating the possibility that the codec(s) will be incorporated into third-party applications and devices.
The following table describes four widely used wideband audio codecs.
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Codec
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Description
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G.722
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- Original wideband audio codec that first described the characteristics of wideband audio (50 to 7,000 Hz)
- High-quality speech applications, including wideband VoIP
- Royalty-free
- Manufacturers make phones that support G.722
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AMR-WB
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- An ITU-T standard speech codec, now codified as G.722.2
- Jointly developed by Nokia and VoiceAge
- First standardized by ETSI/3GPP in December 2001
- ITU-T approved as the G.722.2 recommendation in January 2002
- Applications include teleconferencing and voice-over-packet
- Mandatory standard codec for wideband speech in GSM and Wideband Code Division Multiple Access (WCDMA) networks
- Included in the CableLabs PacketCable 2.0 specification
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RTAudio
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- Microsoft® adaptive wideband audio codec used by Microsoft® Office Communications Server
- Use is growing as the number of deployments of Office Communications Server in enterprise networks increases
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SILK
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- Skype’s wideband audio codec that replaced the Sinusoidal Voice Over Packet Coder (SVOPC) codec
- Royalty-free license made available in March 2009
- Other devices and applications can implement SILK in non-Skype devices
- July 2009, Skype submitted the SILK codec description and payload formats to the Internet Engineering Task Force (IETF)
- March 2010, Skype submitted updated SILK codec descriptions and source code to the IETF
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The following figure depicts an example of the use of wideband audio between two enterprises that support different codecs.
Headsets and Handsets
To support wideband audio, headset/handset equipment must support the relevant codec and have enhanced acoustics in the form of microphone and speaker capabilities. IP-PBXs, SIP phones, and mobile devices are increasingly supporting HD Voice as a standard. Manufacturers are incorporating HD Voice into their SIP Phones, and mobile device manufacturers, are incorporating wideband audio into their mobile phones.