Partiels (1975) is a defining piece of Spectral music by Gérard Grisey whose opening is derived from an electronic sonogram analysis of the attack of a low E2 on a trombone. This spectrum is orchestrally synthesized through the assignation of different instruments to each partial in such a way as to harmonically and gesturally model the dynamic temporal evolution of the attack. Many second and third generation spectral composers cite Partiels as causing their initial interest in the spectral outlook.
Thus the opening features the successive entrance of lower partials with the fifth and ninth partials being louder than lower ones, including the fundamental, and all higher partials gradually trailing off in amplitude. Each partial is approximated to the nearest quarter tone. A low bass reinforces the fundamental an octave lower on the open E1 string which is central to Les Espaces Acoustiques cycle of which Partiels is a part.
The piece also makes use of sum and difference tones to create harmonies.