I’ve had a paper accepted to the Journal of the Audio Engineering Society based on some of the work from my thesis. It was published last week.
The title is “Extended Energy Vector Prediction of Ambisonically Reproduced Image Direction at Off-Centre Listening Positions“. It presents an extension to the energy vector (rE) of Gerzon used in the Ambisonics literature. The extension allows for better prediction of localisation for listeners who aren’t equidistant from all loudspeakers.
It basically adds elements of the precedence effect (or “Law of the First Wavefront”) to the energy vector. This means it can now be used to predict time-delay panning, in addition to amplitude panning.
You can download the paper in the AES e-Library:
- P. Stitt, S. Bertet, and M. van Walstijn, “Extended energy vector prediction of ambisonically reproduced image direction at off-center listening positions,” J. Audio Eng. Soc., vol. 64, no. 5, pp. 299–310, 2016. DOI: http://dx.doi.org/10.17743/jaes.2016.0008
I’ll be posting some supplementary data and tools in the near future. There’ll be some examples of the usage and some listening area localisation maps.
Check back soon!
Our ears use different methods of hearing at different frequencies to allow us to localise sound. We use phase differences at low frequencies and level/intensity differences at high frequency (a slight simplification but it’ll do). Traditional amplitude panning actually recreates these low frequency cues if you’re sitting in the sweet spot i.e. equidistant from both loudspeakers.
But there’s a problem: using the same amplitude across the whole frequency spectrum means that the cues for the low frequency tell your brain that the image is one one direction and the high frequency cues tell it that it’s in another direction.
Perceived localised image position from Gerzon’s Velocity and Energy vectors for standard amplitude panning
A very smart man (which is underselling him) called Michael Gerzon developed two vectors, known as the Velocity and Energy vectors, that can give you an idea of where a sound will be perceived if you know the loudspeaker gains. The Velocity vector is an indication for low frequencies below approximately 700 Hz and Energy vector for high frequencies. If we consider the prediction a standard stereo set-up (2 loudspeakers and a listener forming an equilateral triangle) shown to the right then there is indeed a discrepancy between the directions of the two Gerzon vectors!