Edinburgh-based Wolfson Microelectronics is sampling its first active noise cancellation chip for mobiles.

"Until now, handset manufacturers have been able to reduce noise in the transmit path only, so that background noise is not transmitted to the other party in the call," said Wolfson. "However, they have been unable to do anything about the ambient noise levels near the listener's ear."

The firm's solution is to add active anti-noise cancellation to squash background sound close to the handset speaker.

"Active noise cancellation is a powerful tool for improving the user experience in mobile phones and also improving the economics and user satisfaction of mobile phone networks," said David Monteith, Wolfson's vice-president of business development.

"We are working with a number of manufacturers and believe handsets containing this technology will be on sale internationally during 2009."

The company is not yet revealing details of the chip's operation, but Monteith did confirm that it uses microphones around the phone's loudspeaker to detect incoming ambient sound. The chip then processes this information to generate a signal that can compensate for some of the external sound when it is fed forward to the loudspeaker.

But why not put this technology straight into the phone's baseband processor?

It would be too slow, Monteith told Electronics Weekly. "We are not using standard DSP. This requires very fast processing, and we use some novel digital techniques to do the whole thing faster."

The Wolfson chip includes a speaker amplifier, and so takes up no extra space in phones that already use discrete amplifiers. "Quite a few phones have separate chips to drive the headphones," said Monteith. "There is a desire for disintegration to increase flexibility when new features become available."

This noise cancellation intellectual property came from High Wycombe-based company Sonaptic, where Monteith was CEO and which Wolfson bought less than a year ago.

In January, Wolfson revealed that its silicon carrying similar technology is behind Audio-Technica's recent ATH-ANC3 noise-cancelling headphones.

"Many existing feedback based active noise-cancelling products rely on forming a physical block between the external noise and the user's ears, such as bulky foam casings or deep in-ear plugs, to help improve performance," said Wolfson's CTO Peter Frith at the time.

"Thanks to our feed forward technology, our products effectively lower the ambient noise around a user, removing the need for bulky sound insulation. Furthermore, it only cancels the ambient noise and, unlike the traditional feedback method, does not interfere with music playback."

Audio-Technica seems satisfied. "Wolfson delivers the best noise cancellation performance we have seen to date," said director of engineering Yoshio Aida.

The active noise cancellation intellectual property was the prime reason for acquiring Sonaptic, said Monteith, although it had several other audio processing patents in its SoundStage portfolio.

"As a result of the acquisition we diversified our technology portfolio, expanded our total addressable market and are now enabling more enhanced user experiences," said Wolfson CEO Dave Shrigley.

See also: The Electronics Weekly guide to Digital technology and loudspeaker design