The rich and colourful musical dialogue offered by the combination of flute and guitar in Duo Sostenuto is particularly well suited to the composer's music. 

Indeed, he treats his orchestra like a painter treats his palette, each instrument contributing its own colour. For the flute, it is sometimes its pastoral and melancholic character that is exploited, sometimes its voluble virtuosity that comes to animate the sound fabric, but most often it is used for its soft and clear sound that adds a touch of light to the woodwind section. As for the guitar, it is the symbol of his Spanish dream: in his "Iberias", he surrounds his themes of popular inspiration with a harmonic and orchestral accompaniment evocative of Andalusia: castanets, Basque drums, but also imitation of guitar effects and guitar bandas.