Voip HD Defined and Explained
Iristel announced a high definition (HD) VoIP solution which they say is "High Definition VoIP offers twice the clarity of traditional telephone calls providing for a more life-like and vibrant conversation." We examine that statement and the reasoning, purpose, and technical requirements for VoIP HD.
The standard telephone system is limited. These are the home telephones we all grew up with. In order to allow more long-distance calls to be transmitted, the frequencies transmitted are limited to a bandwidth of about 3,000 hertz. All of the frequencies in your voice below 400 hertz and above 3,400 hertz are eliminated.
Consider CD-quality audio and the Nyquist Theory. This theory is that the actual upper threshold of a piece of digital audio will top out at half the sample rate. So if you are recording at 44.1, the highest frequencies generated will be around 22kHz. That is 2khz higher than the typical human with excellent hearing can hear. At low frequencies the average human can hear frequencies down to 20 - 60 Hertz.
As you can see standard telephones will not approach the full range of audio, nor is quality anywhere near the full spectrum.
For VoIP, or voice over internet protocol, a codecs control the quality. Codecs are used to convert an analog voice signal to digitally encoded version. When you speak the conversion takes place. Assuming the Internet has a broad bandwidth, which it does, it is possible to transmit a decent sound spectrum. That explains why audio and video in a typical YouTube video, if properly recorded, sounds good when you view it.
The same principle applies to VoIP. Take a look at some sample codecs:
ITU G.728 - 16 Kbps
ITU G.729 - 8 Kbps, 10ms frame size
Speex - 2.15 to 44.2 Kbps
LPC10 - 2.5 Kbps
DoD CELP - 4.8 Kbps
Notice how the Speex codec gives a broader spectrum than, for instance, the DoD (Department of Defense) CELP.
Keep in mind that different VoIP providers support different codecs. As far back as December 2004 there were claims about FM quality over IP networks. Called SPIRIT IP-Multi Rate, the improvement was based on the premise that standard ITU codecs like G.729 and G.723 were becoming obsolete.
Without improvements in the standard telephone system, as mentioned above, it will make no difference in a VoIP telephone call once the call is offloaded to the standard telephone system. However, if processing of higher quality VoIP calls, as suggested in VoIP HD, takes place between two or more true VoIP devices using the same codecs, then there should be a noticeble improvement. High Definition VoIP Telephone service means more bandwidth for your conversation, thus better sound quality.
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