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I did some research.
夕べ is the same as 昨夜 (さくや) Here the kanji represent the meaning and not the sound https://japanese.stackexchange.com/questions/271/why-is-昨夜-pronounced-as-ゆうべ-yuube-and-今日-as-きょう-kyou
昨晩 is more formal and less used. A more common way to say last night is "昨日の夜" https://www.italki.com/question/237843
Yahoo search hit amounts confirm these statements:
"昨日の夜" 61.8 million
"昨夜" 2.4 million
"夕べ 1.7 million
"昨晩" 0.6 million
昨晩 is less usedhttps://www.italki.com/question/237843