13. Extended techniques provide composers with more possible

+timbres
+rhythms
+textures
+ensembles

Timbres.

Explanation:

Extended technique is  non-conventional  methods in music produced through act  of singing or playing musical instruments to generate  unusual sounds  or improve the aural quality of a sound, known as Timbres.  Extended technique can vary from performer to performer and depends on choice or style of such performer.