Siegfried Koepf 2011
Tonspiel is a montage consisting of two parts.
In the beginning, Cage talks, referring to Immanuel Kant, presumably to §54. Remark in the Critique of Judgement. The paragraph discusses the aesthetic status of games of chance, music, and wit, which Kant refers to as play of fortune, play of tone, and play of thought. So Cage quotes Kant and says: There are two things that don't have to mean anything, one is music and the other is laughter – and he laughs…
Then music begins to play. The sounds are generated by a set of 24 parallel filters, which break down an audio signal, here taken from John Cage's Writing for the Second Time Through Finnegans Wake (1978), into certain frequency components, inflecting, amplifying or eliminating them. This happens on the basis of a table of pitches representing a sequence of multiply mirror-symmetrical harmonic structures, with which the tuning of the set of filters is continually transformed from one structure into another, creating a new symmetrical frequency spectrum at any given point in time. A subtly microtonal, highly symmetrical process develops, triggered by the input signal and shaped by the harmonic specifications described above.
On the radio program The Artist's Corner, zwölf92 – John Cage 100, 2012.04.07, HR