Amplitude panning is a system that transforms both the phase and amplitude differences of a signal recorded by stereophonic reception systems into amplitude differences reproduced by two speakers. This stereophonic reception systems are usually microphone stereo pairs or the human ears. Amplitude panning is the basis of several multi-loudspeaker configurations. This system derives from stereophony and was originally created by Blumlein around 1930.
Amplitude panning involves a couple of techniques, being pairwise amplitude panning and vector base amplitude panning the most common ones.
Pairwise amplitude panning is based on the tangent law of trigonometry and it is an essential part of traditional horizontal configurations. These settings have attached speakers that are able to reproduce amplitude differences. Within pairwise amplitude panning, an identical sound signal is generated from a set of speakers that are equidistant from the listener and located in different positions. When both speakers are at the same level, a virtual sound source will emerge from the centre. This virtual source of sound will gradually shift towards the higher output speaker as the differences in amplitude increase. The user will be able to achieve the best directional output when the actual location of a speaker is the only source that generates sound. This happens because virtual sources will be less defined.
Vector-based amplitude panning is an amplitude panning technique that is capable of positioning virtual sources in random 2D and 3D loudspeaker setups. These setups might have speakers above or below the level of the human ears. It’s worth mentioning that this arrangement is typically used in places such as concert halls, cinemas and theatres. Within these scenarios, triple-wise panning is required. Triple-wise panning refers to the use of triangle loudspeaker setups that help with the reproduction of virtual sources.
3D loudspeaker setups are not very effective for amplitude panning reproduction, since a generalized tangent law is unable to calculate panning from random speaker locations or for spherical coordinates. Because of this, it’s essential to use a generic reformulation of the tangent law, which defines panning with vector bases, as well as the positions of virtual sources using directional angles. It’s worth mentioning that sometimes the same signal is reproduced in different places with different speaker configurations.