What we did
This is a sponsored PhD project by Paul Power from the University of Salford. We are investigating one of a number of techniques that could deliver the next generation of surround sound. Ambisonics, which was invented in the 70s, is capable of delivering with-height (or '3D') audio to many different speaker layouts using only one set of signals. This project is looking at how such a system can best reproduce with-height audio and what impact the height has on the listening experience.
Why it matters
Surround sound has been standardised and a vast amount of research has been carried out into the perception and the benefits it brings over stereo formats. Since viewing has been enhanced and moved into high resolution it seems that audio has been neglected.
It is therefore necessary to investigate ways of enhancing the listening experience, and find new ways in which we can make this experience more exciting and better for the listener, however at the same time still keep systems manageable for broadcast and storage. It is necessary therefore to quantify the benefits for the user by carrying out a thorough investigation of the user experience, combining subjective evaluation and objective measures.
Our Goals
- Identify the optimum reproduction resolution with respect to human hearing
- Investigate viable with-height speaker layouts
- Identify the improvement height brings over current formats
- Explore the user experience in terms of subjective attributes
Outcomes
Dr Paul Power's thesis Future spatial audio: Subjective evaluation of 3D surround systems has been published and is now available.
How it works
Over the past decade there has been a large amount of research into surround systems and it has been shown that there are a number of attributes which make up a subjectively pleasing surround reproduction, one of these being the ability to localise sources. However, in terms of with height systems, there is not a lot of data available in this respect.
Since Ambisonics provides different resolutions of reproduction at the expense of increasing speaker numbers, and since human hearing is not as accurate in the vertical as in the horizontal, localisation tests have been carried out. These will determine if there are significant differences between various Ambisonic orders for elevated positions around a listener, and inform as to whether higher order material is needed for elevated sources or not.
Another important attribute in surround reproduction is spatial impression which can be broken down into two constituent components - apparent source width and envelopment. Since there is no standard layout for surround systems with height, the next stage is to investigate a number of different layouts subjectively and objectively to find the optimum configuration to produce an enveloping sound-field.
A number of different speaker configurations have been modelled and tested using an objective measure (inter-aural cross correlation) to find the optimum layout. The next stage will be to execute a subjective evaluation of the most promising layouts and collect subjective data, which will then lead to a more in-depth evaluation.
