This article originally appeared in the June 2012 issue of INTERNET TELEPHONY.

Enthusiasts have been beating the drum for HD (wideband) voice for over a decade, but call quality seems always to get worse, not better. So where's the disconnect?The global telephone system is a wonder of interoperability. Any phone can complete a call to any other phone, with the signal flowing through a patchwork of different technologies of different vintages. The downside of this is that the call quality is only as good as theweakest link in the chain. Your ear can hear frequencies up to about 20kHz, but the POTS connection from your house to your local central office is based on hundred-year-old analog technology that can't convey frequencies above 3.4kHz.

Digital technology, based on time division multiplexing, came to the phone network about 50 years ago. The TDM network is incapable of carrying audio frequencies above 4kHz. Over the past 20 years, TDM technology has been progressively displaced by IP technology, which has no intrinsic limit on the audio frequencies that it can carry.

But, still, virtually no calls are wideband.In mobile phone systems the backhaul connections from the cell towers have until recently been bottlenecked through TDM. But mobile phone networks have a tougher problem. The weakest link in a cellular call is the over-the-air connection, which suffers not only from dropped packets,but from bandwidth starvation: a TDM circuit runs at 64kbps, while a cellular connection over the air must get by on a fifth of this.The network transcodes, or converts, a call to match the technology of each part of the patchwork it traverses. Transcoding is like a ratchet; each step makes the call quality worse –never better.

So the secret to high-quality calls is to eliminate transcoding. If the network isIP end-to-end, this is technically trivial, but in practice network engineers sprinkle transcoders liberally to help with interoperability.Finally, there is light at the end of the tunnel. Orange (News - Alert) first deployed wideband in Moldova in 2009, and has since extended it to several other countries in Europe including the U.K., Spain and France. At the beginning of 2011, Verizon (News - Alert) announced it planned to do the samething, but it has been beaten to the punch in the U.S. by Sprint, which in April announced a new phone – the HTC (News - Alert) EVO 4G LTE. 

Calls over the Sprint network with this phone at both ends (and with other phones not yet announced) will be in wideband. What’s cool about this solution is that unlike with Verizon, wideband capability is not confined to calls over LTE (News - Alert). This is because it uses a new codec from Qualcomm called EVRC-NW, which, ingeniously, is backward-compatible with Sprint’s narrowband infrastructure.