( It ( ( ( is well ) ( known ( that ( ( ( sound waves ) ( of ( two ( ( slightly different ) frequencies ) ) ) ) ( create ( ( a ( ` ( beat ' ) ) ) ( note ( as ( ( the waves ) ( interfere ( with ( each other ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (ADVP (RB well)) (VP (VBN known) (SBAR (IN that) (S (NP (NP (JJ sound) (NNS waves)) (PP (IN of) (NP (CD two) (ADJP (RB slightly) (JJ different)) (NNS frequencies)))) (VP (VBP create) (SBAR (S (NP (DT a) (`` `) (NN beat) ('' ')) (VP (VBP note) (SBAR (IN as) (S (NP (DT the) (NNS waves)) (VP (VBP interfere) (PP (IN with) (NP (DT each) (JJ other)))))))))))))) (. .)))
It is well known that sound waves of two slightly different frequencies create a 'beat' note as the waves interfere with each other.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NNS waves)) (PP (IN of) (NP (CD two) (JJ different) (NNS frequencies)))) (VP (VBP interfere)))) (, ,) (NP (NN beating)) (VP (VBZ occurs)) (. .)))