Having a calming voice like that of John Cleese or Ozzy Osbourne shout out directions to supplement the visuals on your GPS navigation device is an effective way to make sure that you don't miss your turn. Relying on visual navigation is a big distraction for cyclists too, dangerously diverting focus away from the road ahead. To help overcome such issues, a research team in the Netherlands has reported promising results from an audio-only navigation system that uses an Android smartphone connected to a pair of headphones to help guide users to a target location with music that's artificially shifted to the left or right to indicate direction.

Headphone-based audio navigation aids have already been the subject of some research - such as helping visually impaired folks to get around, exploring virtual environments, improving safety for car drivers, airplane navigation, and in situations where looking at screens is not possible (such as when wearing helmets or pressure suits).

In a country where folks are said to travel twice as far by bike than on foot, four User System Interaction trainees from Eindhoven University of Technology have developed a tuneful variation of a GPS navigation system to help cyclists get around without having to keep diverting attention from the road ahead.

Where other audio-based systems incorporate different tones to represent various objects and waypoints, the team decided that its user base would only need simple directional prompts and felt that although a continuous tone could be used, this was not best suited for use in urban environments so opted to use a music source instead.

Let music show the way

The 3D-audio system makes use of our ability to detect the direction of a sound source. When a sound is heard, the human brain calculates the (often slight) difference in sound hitting each ear - a sound to the left of the listener will reach the left ear before it reaches the right - and so works out approximate direction and distance. Artificially altering the perceived direction of the stereo audio in a user's soundscape can therefore be used as a guide to a predefined location.

The team experimented with a navigation system made up of a GPS receiver, an electronic compass, some sort of computational device that also has audio output and a pair of headphones. To test the concept, a series of music localization and music navigation experiments were conducted.

For the music localization tests, two static, blindfolded participants were asked to point at a moving object based on the sound emitted from it. The second experiment involved hiding a sound source in a complex environment and asking the blindfolded participants to identify the object's location when the music started to play.

Blindfolded participants were then given headphones connected to a laptop where the sound was shifted from left to right by software, resulting in reasonable spatial accuracy. Next, the team used a moving sound source or beacon instead of headphones, followed by users having to follow a sound beacon around a maze created from office furniture where it was noted that users tended to head for the beacon by the shortest route, so if it turned a corner the user would follow in a straight line and bump into obstacles.

For the final experiment in the music-based navigation tests, two sound beacons were placed either side of the user, which were alternatively activated to indicate direction - making it possible for the participants to navigate complex environments.

Out of the lab and into the real world

The students then created an audio-only navigation prototype from a pair of headphones housing an Android smartphone positioned above the user's head. After working on an algorithm to calculate the correct audio balance needed to determine the angle between the user's head orientation and the target location, a software application was developed to artificially shift music played back through the headphones between left and right channels according to user location and orientation. The volume of the music was used as an indication of distance.

Making use of the built-in GPS and electronic compass of the HTC Hero Android smartphone, two different real-world evaluation tasks were developed - pointing to a location and finding a distant target.

For the pointing test, four users stood in an open field and were asked to determine which of five surrounding buildings had been selected as a target. No mistakes were made and users made their choices quickly. Moving onto the distant location test, two participants were instructed to travel about 1km (0.62 miles) from the starting point to an unknown location by bike. The only guidance received during the journey was from the 3D-audio system. The only mistake was to slightly overshoot the target.

"At the moment the prototype only works for predetermined locations," the team's Daniel Tetteroo told Gizmag. "However, we are busy developing it into a full application that supports navigation to basically any place in the world. The finished application will be available soon through the Android Market. Some of us have already used the limited application in real life and we're very enthusiastic about the concept. It's not just that it is an intuitive and easy way to navigate; it also has a certain fun-factor to it. More adventurous than just following direct instructions which turns to take, as you can just choose directions yourself, and still end up at your final destination."

Although it's true that some cyclists do use music players while on the move, cutting off or dulling the senses in this way could have a negative impact on road safety. The 3D-audio navigation system might therefore be used with headphones that use microphones to feed in external sounds for improved awareness of what's going on around the user.

If you live in the Stockholm area, you can download a free special edition of the app produced for the Mobile HCI conference by team members Tetteroo, Matthijs Zwinderman, Tanya Zavialova, and Paul Lehouck, and give it a try for yourself (Android 2.1 or later required).

The following demonstration shows the Oh Music, Where Art Thou? system being used: