のを聞けば

if you hear …

→ の

phrase Rare #37,634

if you hear … の turns the preceding clause into something heard; を marks it as the object of 聞く (to hear), and 聞けば gives the conditional “if you hear.”

JA: 彼が歌うのを聞けば、きっと驚くよ。

EN: If you hear him sing, you'll surely be surprised.

彼女が笑うのを聞けば、彼女を少女と思うでしょう。

If you heard her laugh, you would think she was a young girl.

私は彼女が話すのを聞けば聞くほど、彼女が好きでなくなる。

The more I hear her talk, the less I like her.

彼が話すのを聞けば、彼を外国人と思うだろう。

If you heard him speak, you'd think he was a foreigner.

彼がフランス語を話すのを聞けば、フランス人だと思うでしょう。

If you heard him speak French, you’d think he was French.

君が歌うのを聞けば人は君を少女と間違えるかもしれない。

People might mistake you for a girl if they heard you sing.