The beginning of the piece in particular highlights perceptual challenges in a very concrete way.
The piece begins with elevated sine tones that quickly descend to the horizon, accompanied by a falling pitch. It then remains at a 45-degree angle, at which point the human auditory system is particularly sensitive. However, due to the nature of the sine tone, it is difficult to localise sharply, and its perceived localisation shifts depending on the listener's seating position.
Slow amplitude modulation makes it easier to localise, as the pulsing adds slow attack timings to the sound. However, it is only when more harmonics are added to the sound that its localisation becomes much sharper.
Spatial Analysis & Visualization
As mentioned previously, my work 'In Motion' is composed in 7th order Ambisonics specifically for hemispherical loudspeaker arrays. In this spatial composition, I wanted to highlight the different ways in which spatial movements and motion can be worked with. Throughout the piece, several variants of movement and their variations are showcased, each of which also highlights different intricacies and challenges in relation to auditory perception.
Various examples will be given and explained in detail alongside the visual analysis of the different sections. In total, I analyse the first three minutes and a later sonically more dense part of the fourteen-minute composition in this exposition. Besides pictures with annotation, I also add short animated GIFs of the Spatial Analysis when a still picture cannot tell the whole story. The GIFs are each 20 seconds long and are looping.
To the first sine tone comes a second one on the right side, which is already richer in overtone spectrum. It's getting spatialized with a room virtualization, which leads to a denser spatial image.
A third sound is added that starts from below the hemisphere and rise up to an elevation of 45°. It gets again accompanied by a pitch bend, this time from a lower note to a higher one, to aid in the perception of a rising sound. The other two sounds are now both pulsing, and further overtones are getting added.
The last section of the composition features a rich soundfield, consisting of binaural field recordings of the composer walking. A recording of far away bells is getting introduced, together with sine tones moving in circles and bird chirps in the upper hemisphere.
As the soundfield is quite dense, spatial distribution helps with auditory stream segregation.
In the middle section, church bells are getting introduced in spatialized using the pattern of a double pendulum. The movements are mostly taking place on the horizon but through the addition of reverberation, the whole spatial image is getting more diffuse.
The spatial visualization clearly shows the circular movements of the sources and also the more diffuse spatial image when sources should be perceived as being further away.
The third sound is visible as an elevated source. To aid the perception of a sound approaching, it is getting granularized which is also visible in the spatial analysis.
Spatial Analysis show the movement of sine tones and also slightly the upper movement of the bird sounds.
Adding of overtones leads to sharpening of the source, which is not visible in the spatial analysis.
