( ( To ( be ( considered ultrasound ) ) ) ( , ( ( sound waves ) ( ( must ( have ( ( ( ( a frequency ) ( ( ( greater ( than 20,000 ) ) Hz ) ( -LRB- ( ( 20 KHz ) -RRB- ) ) ) ) , ) ( rendering ( them ( inaudible ( to ( human ears ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (S (VP (TO To) (VP (VB be) (VP (VBN considered) (NP (NN ultrasound)))))) (, ,) (NP (JJ sound) (NNS waves)) (VP (MD must) (VP (VB have) (NP (NP (NP (DT a) (NN frequency)) (NP (NP (QP (JJR greater) (IN than) (CD 20,000)) (NNS Hz)) (PRN (-LRB- -LRB-) (NP (CD 20) (NNS KHz)) (-RRB- -RRB-)))) (, ,) (VP (VBG rendering) (S (NP (PRP them)) (ADJP (JJ inaudible) (PP (TO to) (NP (JJ human) (NNS ears))))))))) (. .)))
To be considered ultrasound, sound waves must have a frequency greater than 20,000 Hz (20 KHz), rendering them inaudible to human ears.
(ROOT (S (NP (PRP You)) (VP (VBP call) (NP (NP (NN sound)) (SBAR (WHNP (WDT that)) (S (VP (VBZ has) (S (NP (DT a) (NN wave) (NN frequency)) (ADJP (JJR higher) (SBAR (IN than) (S (NP (DT the) (JJ human) (NN ear)) (VP (MD can) (VP (VB detect) (NP (NN ultrasound))))))))))))) (. .)))