Which section is not in the orchestra palette

An orchestra is defined as a large instrumental ensemble typical of classical music. An orchestra features bass, brass, strings, woodwinds, and percussions. In the list given above, the section that is not one of the four groups in the orchestral palette is the voices. The answer would be "voices". 

Well the orchestra is all string instruments except of their are singer so singer or the voices may be the answer

ok

Explanation: