Wideband audio boosts VoIP quality

* Delivering superior audio quality of wideband codecs

Wideband audio boosts VoIP quality

By Michael Ward

Companies have rapidly deployed VoIP technology to reduce operational costs and increase productivity by integrating telecom services with other enterprise workflows. However, the codecs most widely used today that let speech be transmitted over IP data networks do not reproduce speech faithfully for a variety of dialects.

Typical human speech, while consisting of a wide range of frequencies, is very well reproduced by sampling frequencies up to 10KHz. Unfortunately, most VoIP codecs capture well under a half of this frequency spectrum. The G.729 voice codec, one of the most common codecs used in VoIP systems, is a narrowband codec that samples across a frequency range from about 200Hz to just under 4KHz. As a result much of the frequency spectrum of typical human voice is not captured.

To minimize the amount of data required to encode the sampled speech to limit the requirements of network bandwidth as much as possible, algorithms such as G.729 use a variety of encoding techniques that make certain assumptions about speech.

In many cases these assumptions have been made based on a hypothetical Western male voice. These predictive encoding techniques coupled with the limited frequency sampling result in a voice codec that poorly recreates Asian speakers because of the higher frequency content of many Asian dialects. These narrowband codecs also do a poor job in the transmission and encoding of music.

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Ward, director of product line management at Trinity Convergence, can be reached at mward@trinityconvergence.com.
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