The two pieces share the basic sound source and the manner of creating development. The main differences are found in the spatialization methods, and the use of different shapes of modules and trees. It implies that the audio feedback sound created by the resonance of the space, two microphones, and loudspeakers goes through different paths, and therefore different results are encountered. In this chapter the methods shared with the WFS piece are not repeated.
8 channel sound system
An 8-channel system with a circular configuration is chosen because it can be regarded as one of the conventional multichannel setups. The 8 loudspeakers surround the audience, and ideally the performer is located in the center. However, in a concert place where there is a clear division between the stage and the seats for the audience, the performer often stays more to the front side of the speakers.
Figure 8. an octophonic system setup
Different from the WFS system, there is no single method and tool for creating a spatialization for the setup, and a very accurate, complicated trajectory is not as feasible as in the WFS system. While in the WFS system, small loudspeakers generate a sound movement or localization precisely, each speaker in the 8 channel spreads sounds over larger angles. Such characters that the 8-channel configuration provide make it possible to think of ‘zones’, that are varying their shapes over time. Moving sources are possible as well, and there is a variety method to create a specific movement such as Ambisonic panning, equal power azimuth panning, and vector-based amplitude panning.
Figure 9. Stereophonic configuration formulated with vectors.
Before making a choice between different panning implementations, it was necessary to make a comparison between them. In SuperCollider, I have compared BiPanB2 / DecodeB2, a 2D Ambisonic B-format panner, PanAZ, a Multichannel equal power azimuth panner and VBAP, a vector-based amplitude panning. The tests are made with simple trajectories: a straight line crossing the space, a circular motion, and a figure of eight motion. A Doppler effect is applied to each method, and white noise was used as a sound source. In the following chapter the application of the Doppler effect is explained.
The experiment gives a rather unclear answer, meaning that each panning method did not provide a distinctive difference in the spatial perception. Then the choice was made based on the feasibility to alternate the speaker configurations. This means that a different shape of the 8-loudspeaker configuration in a concert hall can be easily adapted. VBAP provides a simple solution. In VBAP, the number of loudspeakers can be arbitrary, and they can be positioned in arbitrary 2-D or 3-D setups. VBAP produces virtual sources that are as precise as is possible with current loudspeaker configuration and amplitude panning methods, since it uses at one time, the minimum number of loudspeakers needed; one, two, or three. It uses a buffer to store the speaker configuration with an array. For example, an array of [0, 45, 90, 135, 180, -135, -90, -45] implies the angles of each speaker and the order of the speaker array, starting from the center front (0), front-right (45), center-right (90), and so on. Simply by changing the values of the angles, every module with a VBAP is adapted to a new configuration, as they share the same buffer.