, ▁and ▁ 3 ▁br ass ▁instruments ; ▁and ▁Section ▁G ▁util izes ▁wood w inds , ▁ 3 ▁timp ani , ▁ 3 ▁br ass ▁instruments , ▁and ▁piano . ▁Ex cept ▁for ▁section ▁E , ▁each ▁subsequent ▁ref rain ▁adds ▁duration ▁in ▁multi ples ▁of ▁ 6 ▁seconds . ▁Thus , ▁the ▁dur ations ▁for ▁each ▁section ▁are : ▁A - 1 2 ", ▁C - 1 8 ", ▁E - 6 ", ▁and ▁G - 2 4 ". ▁ ▁Se ctions ▁B , ▁D , ▁F , ▁and ▁H ▁function ▁as ▁contrast ing ▁inter l udes . ▁Similar ▁to ▁the ▁ref ra ins , ▁per cussion ▁instruments ▁signal ▁the ▁beginning ▁of ▁these ▁sections , ▁which ▁are ▁composed ▁of ▁static ▁soft ▁string ▁clusters . ▁ ▁Another ▁notable ▁feature ▁of ▁this ▁composition ▁is ▁L utos ław ski ' s ▁hall mark ▁use ▁of ▁a ▁twelve - t one ▁ch ord . ▁L utos ław ski ' s ▁twelve - t one ▁ch ords ▁are ▁symmet rical ▁and ▁often ▁use ▁a ▁limited ▁number ▁of ▁intervals . ▁For ▁example , ▁the ▁wood wind ▁pitch es ▁of ▁section ▁A ▁contain ▁ 1 2 ▁notes ▁and ▁exhib it ▁the ▁following ▁inter v all ic ▁structure ▁from ▁bottom ▁to ▁top : ▁ 2 3 2 2 2 ▁/ ▁ 5 ▁/ ▁ 2 2 2 3 2 . ▁Thus , ▁such ▁ale ator ic ▁counter point ▁produces ▁a ▁special ▁type ▁of ▁sound ▁mass ▁in ▁which ▁the ▁full ▁chrom atic ▁spectrum ▁is ▁not ▁covered . ▁R ather ▁than