5. COMPOSITIONAL APPLICATION

We have at our disposal now a system for specifying the angle and elevation of one stereo or two mono sources, plus related distance cues like amplitude, reverberation and equalization characteristics and even Doppler effect if wanted.

The software enables one to choreograph movements in real time with the mouse and foot pedal. If the MIDI interface is not fast enough for the data volume, or repetitive patterns are wanted, the spatial samples option is used to currently send over a thousand coefficient sets per second to the channel cards. These spatial samples can be controlled via MIDI much like (or even in tandem with) a conventional sampler.

The signals are handled in a way that requires only four channels to adequately describe a complete 3D soundfield, and these four channels can be handled in the studio in similar ways to our familiar stereo pair. [29] [30] are interesting accounts of putting together Ambisonic studio setups, with the technology of over ten years ago. Groups of B-format signals can easily be added together on multitrack tape, building up complex layers of moving sound. The Soundfield microphone may also be used to originate audio and this may be layered with synthetically placed sound. A sixteen track ADAT as used currently at ACAT can hold 4 B-format signals, each of which could have originated as a stereo pair or two mono sources, eg. synthesizer outputs. The limitation of four groups can be overcome by the (old-fashioned) technique of "bouncing down" three groups to one on the ADAT, which is sonically transparent enough to handle at least a few generations of this without audible degradation.

The final mixed sound must end up on a four track (or greater) medium, with minimal phase difference between the tracks. For this purpose, a semi-pro analogue recorder is not ideal, since exact phase correlation is hard to achieve between all tracks. A digital multitrack like the ADAT or DA-88 is much more suitable in this regard. These comments also apply to location recordings made with a Soundfield microphone.