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Thursday, May 12, 2011

There’s Just No Excuse for Bad VoIP Voice Quality


Today’s  VoIP quality can be better than traditional fixed-line voice (PSTN)
Ali Kafel – May 12, 2012

Remember the days when voice quality (using VoIP) was really bad? For some, I suspect you are thinking   “what do you mean were?”. Well, if you are one of those people that are still experiencing bad voip quality, you may want to change your service provider or your equipment vendor, because there is no reason any more for poor quality VoIP service especially over a private IP network.  in recent years, because of increased bandwidth  and also because of advancement in compression and quality-of-service techniques, VoIP quality has significantly increased even over the public Internet, and in many cases it is hard to believe  that it is a VoIP call when using services like Vonage, Skype or MagicJack.

OK, now you may be thinking, this makes VoIP better than it was before and maybe in par with the PSTN when it is carried over a private IP network, but how does this make it better than PSTN?. Have you ever wondered why the sound of letters like “F” and “S” and “M” and “N”, or words like “goal” or “gold” sound very similar on a traditional phone (mobile or fixed-line) connection? In simple terms, it is because some of the sound spectrum is lost in translation.  A conventional analog telephone system works like this: it converts acoustic signals (human voice) to electrical signals, transmits them through a wire (or over the wireless spectrum) and then on the other side converts them back to an acoustic form before the sound can be heard by the human ear.  The frequency range that the human voice can produce ranges from 30 to 18,000 Hz , and the human ear  hears sound between similar  frequency ranges. However, when engineers originally designed telephone communications, they determined that most of the energy necessary for intelligible speech that would be noise free when carried over analog circuits was between 200Hz to 3400 Hz. Therefore they designed the PSTN to operate in that range and filtered out other frequencies.  The problem is that certain consonants sound nearly identical when the higher-range frequency is removed. This includes the sound of letters or words mentioned above. In today’s state-of-the-art VoIP (Voice Over IP) networks, the use of wideband codec doubles sound spectrum captured, to the range of 30 Hz to 7Khz. This creates significant clarity to the transmitted sound, that is better than the PSTN, without increasing capacity.-And with compression,  the bandwidth requirement reduces  to 32Kbps, half that of PSTN – truly getting more for less.  This is referred to as high-definition (HD) voice, or also called wideband voice. Beyond the codec in the VoIP handsets, the IP core/interconnect network also plays a critical role in enabling HD voice communications. In order to establish and maintain an end-to-end HD call, the IP core/interconnect network must enable the interworking of multiple heterogeneous devices and access networks, and it must do so efficiency and cost effectively.  

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