Classes of Musical Source Sounds and Environments:

The Monophonic Source

The monophonic signal is well-known and understood. It consists of a single signal trace. It appears unequivocally at the emitting loudspeaker. Any reverberant or ambience traces embedded in the signal appear as artificial, and do not contribute to the ambient sense of the array.

When sent equally to two identical loudspeakers, the monophonic source appears as a phantom image between them, subject to the rules for phantom images.

The stereophonic source

A stereophonic source consists of two partially correlated signals. Subject to the rules for phantom images and phantom reverberance, it appears as a phantom image between the two loudspeakers, with a phantom ambient or reverberant field stretching between (and sometimes outside of) the stereophonic array. For a signal pair to be sufficiently correlated to qualify as stereo, the amplitude difference between the signal artifacts on the channel pair needs to be less than 8 dB and the time difference needs to be less than approximately 40 ms.

The 6- iteration source

A 6-channel source is conceptually similar to the Ambisonic B-format signal. It includes a correlated array of artifacts that both serve to localize a single phantom image or images somewhere on or beyond the surface of the sound field, as well as to carry the enveloping ambience and/or reverberance that accompany such an artifiact.

Complex 6-channel voice arrays

A complex 6-channel voice array includes both a group of related sources (which are usually monophonic) that have a specific musical function (a hocket, an echo-loop, a chord or cluster, etc.) plus (usually) an associated ambience and or reverberance.

Ambience & Reverberance in 6 channels

At present, surround reverberators are configured for conventional surround topographies, and include no provision for height channels. My solution has been to appropriate the center channel for a height channel and reconfigure the reverb (I am using a Lexicon 960) so that the center channel is picking up in the center toward the rear. I find this works in a generally convincing way.

Another reverberant possibilitiy exists: a reverberant environment that includes no source sound, and either decays or grows (if the reverb is reversed) independently of such ommitted source sounds. There is no acoustical equivalent to this behavior. Surprisingly, it is generally quite beautiful and moving, a very powerful musical gesture and condition.

Additive Synthesis, Subtractive Synthesis and Samples

The creation of source signals can be done a variety of ways. I have used conventional synthesizers, “found” recorded source beds, and manually generated tones. I am looking forward to the use of high quality “orchestral source” samples, but am unsure of how such cognitively association-loaded sources will fit into my sonic landscape. At present, I am working almost exclusively with sine, square and sawtooth waves, with white and pink noise, and with reverberance in a kind of additive synthesis realm.

Intonation, Beating and Fine Tuning Issues

An extraordinarily interesting and powerful effect unique to loudspeaker arrays (and synthesizers!) has to do with the use of precisely tuned interval ratios. It is now technically trivial to tune to precisions of .001 Hz (one complete phase shift every 17 minutes). This leads to the generation of “beat-free” chords that are unprecedented in musical performance, with an entirely different sonic character and emotional affect. Distributing an absolutely beat-free 6 part open-voiced C-major chord among 6 speakers, for instance, yields some remarkable sensations, including a quality of sonic envelopment that is quite unique, as well as a striking and almost liquid Doppler shift that accompanies any and all motions of the listener, leading to a swimming sense of immersion within the chord.