Spectrum was originally written in 1975 and revised in 2013. It was written for Derek Foster who played it on a number of occasions.
The work lasts around 4.5 minutes, although the precise duration cannot be specified as there is a degree of freedom in the presentation of the material. It opens with a rising chromatic figure that is used throughout the piece, followed by three notes which are at first stated, then developed freely. A short faster section follows and consists of tremolos and trills together with a very rapid figure. The central section develops trills, tremolos and rising chromatic phrases. This is followed by a reprise of the rapid section, then the first section, forming an arch-like structure (A-B-C-B-A).
The title derives from the use of a variety of techniques and contrasting material on a single instrument. The composer sees this as analogous to the electromagnetic spectrum in physics where one single type of waveform can manifest in a number of totally different ways, such as radio waves, light waves, X-rays, etc.