Composer's Notebook: Star Networks at the Singing Point

Abstract

Star Networks at the Singing Point, poetic though it sounds, is merely a description in engineering terminology of the sound-producing method that forms the basis for the piece. A "star network" is a circuit node having three or more connections. The "singing point" is the particular tuning at which the gain in a feedback circuit produces oscillation. In Star Networks at the Singing Point, the performer creates analog circuits composed of multiple nodes, each of which has three or more connections—in essence, "mazes" having a number of paths through which current can flow. Connecting such a circuit in a feedback loop around a gain stage produces an oscillator that is inherently unstable. Tuned to what is called in chaos theory a "tipping point," the circuit sings unpredictably of its own accord.

Star Networks at the Singing Point: Performance Instructions

Star network: a set of three or more branches with one terminal of each connected at a common node.

Assemble a diverse collection of both fixed and variable passive circuit elements such as:

• inductors (toroids, chokes, coils)

• transformers (impedance-matching, interstage coupling,

• phase-shifting, pulse, rectifier, variable-voltage, etc., windings tuned or untuned)

• capacitors

• potentiometers, rheostats, L-pads

• passive delay lines

• rectifiers

• crossover networks, passive filter blocks, or other found networks

Cover a wide range of values in each class; include parts of unknown values.

Arrange these elements so that they may readily be connected in various ways. Use patch panels, proto-boards, switch or pin matrices, spring terminals, clip leads, or any other bread-boarding system to provide flexibility. Let the passive components be visible.

Freely connect the passive elements to form

-complexes of interconnected star networks-

which provide both a number of ports to which external gain and output stages may be connected, and a number of interconnected signal paths, the impedance and phase characteristic of each of which varies with frequency.

By feedback through such networks around high-gain stages such as:

• preamplifiers (microphone, phono, tape head, etc., flat or having fixed or variable equalization)

• differential input amplifiers

• differential output amplifiers

• small power amplifiers

form oscillating circuits having multiple interactive loops. Provide control of both gain (from zero to maximum of each amplifier) and polarity of each gain stage. (Control of polarity may be provided, for example, by switching in an active inverter or by switching the polarity of an input or output transformer, where one is used.) Optionally, a mixer (matrix or other) may be used to control the assignment of the gain stages.

Use no other signal-processing elements, either in the feedback loops or at the output stage; no automated control or servo systems should be used.

Take output signals from various points in the networks, pre-amplifying where necessary, and provide for release to a speaker.

• - One speaker per network complex is preferred.

• - Provide a small, independent monitor speaker for use when tuning a network.

In performance:

Monitoring over the small speaker, vary loop gains, the value of variable elements, the assignment of the gain stage or stages, and the connections in a network; tune a sound.

• - Look for unstable oscillatory modes.

• - Operate either at the very onset of oscillation (low loop gain), or at very high loop gain (clipping is permissible, and may be desirable).

When the sound of a network is tuned, release it to the appropriate speaker. Allow each tuning to sing at least five minutes, longer when appropriate.

• - When a sound is singing in a speaker, change the tuning only if necessary to preserve instability of the oscillation.

• - Always switch to the monitor speaker when searching for a new sound.

Ralph Jones, Star Networks Instrument, 1978 (Photo © Ralph Jones, 1980). The instrument, built into a gray molded plastic traveling case, is a collection of elemental analog electronic elements (principally inductors and capacitors, both variable and fixed-value). Surrounding it are tube preamplifiers, which provide gain for oscillation, and a matrix mixer for tuning and distributing the instrument's sounds. Color-coded clip leads are used to make the connections; each circuit uses a different color...