Corresponding letters of the alphabet with 相当

コナン:

「ピアノの鍵盤(けんばん)の左端(ひだりはし)から順(じゅん)に、アルファベットをあてはめて…」

“Starting from the leftmost key on the piano keyboard, I assigned each key a letter...”

「メッセージの文字(もじ)に相当(そうとう)する音(おと)を、譜面(ふめん)に書(か)きしるしただけだよ…」

“I simply wrote down the notes corresponding to the letters of the message on the sheet music...”

Key Points

1. 相当(そうとう)する = to correspond to

   • Here 相当(そうとう)する means “to match up with” or “to correspond to”.

   • Conan is pairing each letter with its matching piano note.

2. に相当(そうとう)する links one item to its counterpart

   • 「メッセージの文字(もじ)に 相当(そうとう)する 音(おと)」 means “the notes corresponding to the letters of the message”.

   • The に marks what those notes correspond to.

3. だけだよ downplays the cleverness

   • Conan frames the method as simple with 〜だけだよ.

   • It gives the sense of “that’s all I did”, even though the decoding was actually quite smart.