Brisbane, September 2008

The premiere performance of codex IX took place in The Performance Space at the Judith Wright Centre of Contemporary Arts in Brisbane, Australia in September 2008. The venue is a flexible theatre space with a retractable seating bank and floor area 15 metres wide by 21 metres long with the seats retracted. Total elevation is 9 metres, with gantries at 6 metres determining the upper limit for speaker elevation.

The ensemble configuration for adopted for this series of codex IX performances consisted of performers seated in a circle, surrounded by the audience. The sound system design for the Brisbane performance of codex IX (developed in consultation

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with composer Richard Barrett) consisted of 16 speakers on discrete feeds arranged in an approximate hemisphere around and above the performers and audience. Around the audience, at ground level, was a circle of eight speakers fifteen metres in diameter.

A further ring of four speakers was suspended at half room height with a smaller diameter approximating points on a hemisphere defined by the fifteen metre diameter of the lower speaker ring. Four more speakers were suspended in a tight ring just below the six metre gantry height, defining the upper portion of the hemisphere.

Figure 8 – Performer and speaker layout for codex IX, Brisbane 2008

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Speaker locations were measured and coordinates entered into the spatialization software by system developers Lawrence Harvey and Jeffrey Hannam, and the software calibrated to allow the vbap algorithm to accurately position sounds at any location on the hemisphere. The spatialization computer’s inputs were fed signals from post fade direct outputs from a Midas Venice 320 mixing console. The spatialization system’s software matrix was then used to route each input either to a vbap algorithm or directly to a speaker as required. Real time performance control for the Brisbane performance was limited to eight MIDI faders, and automated control was only available by means of low frequency oscillator (LFO) modulation of azimuth and elevation parameters. In keeping with the strategy of using spatialization to assist in the differentiation between functional instrumental groupings, we decided in pre-production planning that quintet groups would remain statically spatialized at floor level, trio groups would be rotating slowly under automated control and solo instruments would be moved manually by means of direct MIDI fader control. LFO modulation was applied to the azimuth parameter of each of the vbap panners designated for the trio instruments. A MIDI fader was assigned to control the rate of each of the LFOs and the elevation parameter of each of the vbap panners. The trio instruments could thereby be made to rotate at a variable rate, with their elevation controlled with a fader. The remaining two MIDI control faders were assigned to the azimuth and elevation parameters of the vbap panner designated for the solo instrument, allowing manual control of its position or motion anywhere on the hemisphere.

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Ensemble balance was controlled at the Midas console prior to analogue to digital conversion via two Metric Halo 2882 interfaces connected to the spatialization computer. While this approach fails to take full advantage of the full resolution of the Metric Halo converters, it has the benefit of providing fader control of ensemble balance, and access to input channel equalization in the analogue domain. To simplify the interface with the venue’s sound system, the outputs from the spatialization computer were being routed to speakers via the Digidesign D-Show Profile console housed in the venue’s control room. Because the spatialization software was untried in the context of ensemble performance, a contingency was put into place to guard against failure of the spatialization computer or software. In addition to feeding the spatialization computer from direct outputs, signals from the Midas console group and auxiliary outputs were sent directly to spare channels on the Digidesign console.

These channels were routed via the Digidesign console to the ring of eight speakers at floor level. In the event of spatialization system failure, raising the appropriate output masters on the Midas console would send the ensemble inputs directly to speakers and allow amplified performance to continue while the spatialization system was brought back online.

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Figure 9 – Signal flow for codex IX, Brisbane 2008

The contingency patching proved useful, but not in the way it was conceived.

When excessive signal latency inherent in the path through the spatialization computer became evident in rehearsal, the performance control strategy was modified such that the static quintet routing was handled directly by the Midas console. This made performance control more complex in that numerous group assignments and send levels had to be reset manually with each change in ensemble configuration, a task that was intended to be handled by recalling input matrix states on the spatialization computer. This reconfiguration eased the processing load on the spatialization computer, which allowed the audio buffer size to be reduced in Max/MSP, which reduced the latency but did not eliminate it entirely. Bypassing the

Midas Venice 320 Mixing console

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spatialization computer for the quintet instruments meant they remained latency free.

The failsafe remained in place with the trio and solo instruments simply needing to be routed to speakers from the Midas console in the event of spatialization system failure, which did not eventuate.

Figure 10 – Control position for codex IX, Brisbane 2008⁸

From a research perspective the process was instructive, but from the perspective of the quality of the concert presentation it fell considerably short of ELISION’s established standard of technical production, due to the still audible latency in the spatialization system causing a constant delay that was clearly audible on transients. It was clear that the spatialization software had considerable potential for ensemble performance, but that substantial updating and reworking would be

8 Photograph courtesy Lawrence Harvey

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required for it to be usable in concert. The SIAL software system was subsequently updated by Stephen Adam in order that it be viable for continued research in a public concert environment.