Berio draws innovative sonorities from this ensemble. Each of the woodwinds is at times called upon to produce “multiphonics”: phantom chords drawn from these single-note instruments by the use of special fingerings and careful control of breathing pressure. Five orchestral string-soloists (two violins, viola, cello and bass) subject their instruments to non-standard tunings (scordatura) which allow new arpeggios and harmonics. Strings also occasionally employ an ultraslow bowing-effect to produce a distinctive grinding sound.

The clarinet and viola soloists begin the work unaccompanied, gradually summoning orchestral violas and members of the clarinet family. Soon, the scordatura orchestral soloists appear, deployed against the non-scordatura solo strings' sallies and wind-fragments; then tutti flourishes launch the main body of the work. During the second half of Alternatim, repeated-note figures play an increasingly dominant role in the texture, often muttered in pianissimo spasms. The scordatura soloists reappear before a closing episode, in which the orchestral textures gradually evaporate behind fragmented clarinet and viola comments that evolve toward final stasis. Berio has provided the following commentary:

“The term “alternatim” evokes an antiphonal medieval technique also developed throughout the fifteenth century, featuring alternations between Gregorian chant and polyphony or between voices and organ. However, in this „double concerto'" for clarinet, viola and orchestra, the term is used metaphorically. The musical discourse consists mostly of interweaving lines, whose contours are constantly transformed. All of the musical functions are generated by the soloists. They interact with the orchestra through figures which are more or less similar, more or less thematic and more or less recognizable - these “alternatively” emerge and subside in the orchestral texture and silence.” (Luciano Berio)

From the programme notes by Benjamin Folkman