Sounds spooky? United States-based SRS Labs has developed a way of processing audio to 'trick' the ear into thinking sound is coming from all around when in fact the source is a single or pair of speakers.

In fact, this technology has been around for some time in stereos, but the Nasdaq-listed company has developed a suite of 'sound retrieval system' (SRS) products for use in high-end MP3 players, televisions and mobile phones.

Hong Kong users of NEC's c616 3G mobile phone may have noticed that the handset's audio playback quality defies the miniscule dimensions of its internal speaker.

In home theatre systems, the technology is used to create a 'virtual surround sound' experience from a single pair of speakers.

'SRS technology was created through the understanding of how the human ear and the brain interact with the sound,' SRS Labs sales and business development director Kin Tang said.

'Basically, it's a compensation system. What it compensates for is the difference between the traditional recording and playback system, and the way our human ear actually works.'

At the heart of SRS technology is research done in the field of 'head-related transfer function', or the way the ear and brain work together to determine the direction a sound is coming from.

The outer ear transfers a specific sound frequency to the eardrum at different decibel levels, according to the direction of the sound. Put simply, a single sound frequency will vary in volume if the source is in front, to the side of, or behind the head.

'The head perceives the direction of sound by several means,' Mr Tang said. 'Sometimes it is done by the time of arrival to each ear. The other way is through the characteristics of the sound. Sounds from different angles have different signatures, different characteristics.'

Mr Tang suggested a simple experiment to illustrate the principle.

'Rub your hands together in front of you, then move them around your head. The distance is the same, the source of the sound is the same, but when we hear it we actually notice little changes as the sound enters our ear at different angles.

'Volume and pitch change a little bit, because of the shape of the human head,' he said.

In its earliest incarnation, SRS technology reprocessed ambient sound lost in stereo recordings according to frequency response signatures, effectively recreating the 3-D effect of live music through two speakers.

But Mr Tang said the process was even more effective now that various media, such as DVDs and digital broadcasts, were recorded in multichannel surround-sound format.

The firm's TruSurround technology reprocesses the rear channels to create a 'virtual surround sound experience' without the need for multiple speakers.

'TruSurround is a practical system for Hong Kong, where people don't have a lot of space for six speakers,' Mr Tang said.

'In scenes where you have sound coming from the rear, you can sense it. I don't say hear it because the processing is actually taking place inside the brain, so [SRS] kind of tricks your brain into thinking the sound is coming from those angles.'

SRS Labs has come a long way since it was founded as an offshoot of Hughes Aircraft, the firm that developed the United States' military Apache Helicopter and the Galileo space probe. SRS audio technology has shipped in more than 500 million products from about 230 manufacturers.

'The good thing about this technology is that it's not very expensive. All we are doing is adding one integrated circuit [IC], everything else is in the product already,' Mr Tang said.

'In some cases, we are adding a feature on top of [that which] the IC manufacturers are using already. For instance, if they have a volume-control IC, we can put SRS inside the volume control, so they are not buying another chip, just adding a function to the chip.'

Mr Tang said SRS Labs was focusing on expanding applications for the technology and building the brand. Microsoft has used SRS in its Windows Media Player since version 7, while Kenwood is leading the charge in car audio, where the technology can be used to elevate sound from speakers located near the floor.

Mr Tang said manufacturers were increasingly in a position to charge a premium for SRS-equipped products, and more and more high-end MP3 players and televisions were shipping with the company logo.

'We are not a very well-known company as of now because we are dealing mostly directly with manufacturers and not promoting to the consumers. But hopefully we will get there,' he said.

'If you look at some companies in this market like Dolby and DTS, building a good brand name is very important, so we have to make sure that quality control is there. Everything bearing our logo should sound good. If we keep doing that, eventually the market will get to know us.'