Orange rolls out high-definition voice for mobiles Published duration 1 September 2010

image caption The technology will only work between HD enabled phones on the Orange network

Mobile firm Orange has become the first UK network to use a technology that offers higher quality voice calls.

High Definition (HD) voice claims to reduce background noise and the "hisses and crackles" often heard on a normal mobile call.

The technology, known as, Adaptive Multi Rate Wideband (AMR-WB) has been adopted as an international standard for 3G mobile networks.

Other networks are expected to follow Orange soon, experts said.

"It is relatively easy for an operator to introduce - it's just a software upgrade… in a base station," said William Webb, head of research and development at the UK regulator Ofcom.

Other countries already have networks using the technology - known colloquially as HD Voice - including Moldova and Germany.

Data squeeze

AMR-WB is what is known as a speech codec; software that compresses a voice signal to maximise the amount of bandwidth on a network.

"There is a commercial incentive to squash the data as much as possible," said Mr Webb. "But you can go too far. The trick is to find the balance point, the sweet spot."

He said there had been a lot of experimentation over the years with voice codecs, including the introduction of a so-called "half-rate codec", which squeezed the same data into half the bandwidth.

"Operators tried to use it but quickly discovered that consumers didn't like it and switched back," he said.

Speech codecs work by modelling the waveform of the incoming voice.

Rather than transmitting the whole waveform, algorithms look for consecutive sections that are similar. If two sections of the wavelength are alike, the redundant information is stripped out, allowing the signal to be compressed.

The AMR-WB codec also does this but to a wider range of speech frequencies than today's codecs, allowing higher quality calls.

"We are using exactly the same bandwidth on the network," said Andrew Warner, head of voice and messaging protocols at Orange.

"We are squeezing more speech information into the same channel."

This is important as any additional need for bandwidth would reduce the network's ability to cope with the ever increasing data demands of people browsing the web on their phones.

In addition to compression technology, AMR-WB is "intelligent" and varies the amount of data it pumps into the network depending on the complexity of the speech pattern.

"If the speech is quite complex it may use a higher data rate, if it is more simple it drops down," said Mr Webb.

Orange has already run trials of the technology in the south west of England and now plans to roll it out across the country.

Mr Warner said that many manufacturers were already developing handsets to work with HD voice, including Nokia and Samsung.

The technology will only initially work on the Orange 3G network between HD-enabled handsets.

"You won't experience it when you're calling a landline or a mobile phone that has not been optimised to work with HD voice," said Mr Warner.

Orange, owned by France Telecom, recently merged with T-mobile in the UK. The company - known as Everything Everywhere - has 30 million customers.

The two firms have not merged their networks so T-Mobile customers will not initially be able to use the service.

The launch of HD voice comes amidst reports from Orange customers of regular network outages.