Last month, Genelec introduced its new Aural ID headphone monitoring technology, which constructs a 3D model of the user's head to provide personally-tailored, immersive sound through headphones. Genelec R&D director Aki Mäkivirta gives PSNEurope the inside track on the new software…
Back in March, Genelec announced the arrival of its new Aural ID software technology, which works by acquiring a person’s ‘exclusive acoustic attributes to create a detailed modelling of their unique anatomical features affecting hearing’. Recognising that traditional ‘one size fits all’ headphone reproduction can sometimes fail to yield a reliable reference for audio professionals, Aural ID has been designed to calculate the user’s personal Head Related Transfer Function (HRTF). This describes the acoustical properties of the head, upper torso and external ear: elements that interact in complex ways to affect sounds reaching the eardrums. To help us understand precisely how the new technology can be deployed to maximum effect for audio professionals, PSNEurope spoke to Genelec’s R&D manager Aki Mäkivirta...
How does the new Aural ID software work?
Aural ID is a reliable and accurate method of obtaining your personal Head-Related Impulse Responses (HRIR, in time domain) for hundreds of different orientations of arrival for audio. This information is also referred to as the Head-Related Transfer Function (HRTF, in frequency domain). HRIR and HRTF both explain how sound changes when it travels to your ears from a certain direction. The main changes have to do with amplification and attenuation of certain frequencies depending on the direction of arrival, and the timing and phase relationship related changes in audio, and between the same audio signal arriving at your two ears. These combine to create your sensation of the direction for the audio signal. Aural ID contains this information in a file and is specific to the user.
The Aural ID is a complete acoustic field simulation of hundreds of directions of arrival for sound. The simulation is based on constructing a fully detailed 3D model of the person’s head, external ear details and the upper parts of your body. This model is created based on a video you can take using a mobile phone camera, making Aural ID completely personal. These are uploaded to Genelec's Aural ID service, and the production process delivers the Aural ID in a SOFA format file back to the customer via the service website.
Talk us through the development process of the technology?
Work on Aural ID started several years ago. Audio engineers use monitoring loudspeakers as their sonic reference for monitoring and essentially trust completely in what they hear. They also know that acoustic calibration, such as Genelec GLM software, improves the way studio monitors can perform in an acoustic space. The idea behind Aural ID is to help bring this reliability and sonic truthfulness to headphone reproduction. The use of photogrammetry to map the 3D shape of the head, external ears and upper torso is now feasible with modern computer technology and is increasingly used in mapping terrain, charting archaeological sites, and creating renderings of apartments, statues and other objects. Using this technology for mapping the personal detailed shapes of a listener opens vastly new possibilities. We can calculate the exact characteristics of the audio signal reaching the ear and hence bring all the personal features to determine what changes sound experiences when it arrives to your ears.
How does it change the listening experience for users?
The world is around you, and only recently have those who record and present audio mechanically, using microphones, loudspeakers and headphones, started to approach the true reality of audio. Now, we talk about immersive audio, meaning an audio presentation that actually tries to mimic what we experience in reality. For a wide seating area, we can introduce a dense grid of loudspeakers that everyone in the audience can locate correctly. This includes horizontal and vertical direction, and is the foundation for all modern loudspeaker-based immersive audio presentations. After this comes the challenge of creating virtual sound images between these real sources, which is called panning. Today, we have panning methods that allow us to pan audio inside a triangle formed by the three nearest loudspeakers. The network of loudspeakers forms a number of triangles that can be used in this way to create a full sphere of sound – complete immersion.
When headphones are placed over or inside the ears, the human sound localisation system of the head size and external ear shape is removed from the equation – this is the reason why sound mostly seems to be inside an earphone listener’s head. Once the HRTF measurements exist, for the first time, we have the ability to present sound properly using the headphones. The process is relatively simple but requires an amount of signal processing and the additional information available in the Genelec Aural ID. When the direction of arrival for a certain sound component is known, this sound can be processed with the relevant HRTFs for that particular direction to create the correct directional cues for ears.
The key to enabling this process is having access to the HRTF information. Scientists have found that although we all share the same broad principles in how the HRTF looks, we are all individual with slight differences in details, and these details do not successfully translate from one person to another. Therefore, borrowing someone else’s HRTFs for listening will not be successful. You need your own, personal HRTF information.
Which applications will this technology be most applicable to?
Potential users are those operating in Virtual Reality and Augmented Reality systems, game engineers calculating sound dynamically as part of the gaming process, cinema and immersive audio designers, and researchers working with 3D audio. Ultimately, we all will be able to benefit, once the method of presenting immersive audio develops to include information about sound arrival direction and the processing needed to use personal HRTF information for headphones. This will elevate headphone listening to be more reliable and accurate, closer to using loudspeakers in a good room. In order to use the HRTF data, we need some software that enables one to process the audio to apply the HRTF information. Such software already exists on the market, starting with media player software, VLC plugins for audio workstations intended for professionals, and other more researchoriented implementations. This makes adopting Aural ID technology easy and straightforward.
Aural ID has now been launched and will enter into regular service using the Genelec Community website – www.genelec.com/auralid – during Q2 of this year.