They can change the tone of people's voice yes.
( They ( ( can ( ( change ( ( the tone ) ( of ( ( people 's ) voice ) ) ) ) yes ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (MD can) (VP (VB change) (NP (NP (DT the) (NN tone)) (PP (IN of) (NP (NP (NNS people) (POS 's)) (NN voice)))) (NP (RB yes)))) (. .)))
People's tone of voice can't ever be changed.
( ( ( ( People 's ) tone ) ( of voice ) ) ( ( ( ( ca n't ) ever ) ( be changed ) ) . ) )
(ROOT (S (NP (NP (NP (NNS People) (POS 's)) (NN tone)) (PP (IN of) (NP (NN voice)))) (VP (MD ca) (RB n't) (ADVP (RB ever)) (VP (VB be) (VP (VBN changed)))) (. .)))