間 違 い じゃなかった — Tae Kim's Japanese Grammar flashcard

バカ だった

夢ゆめ

夢ゆめ じゃなかった

Double consonants

Notice the "tt" in janakatta. Double consonants (tt in this case) prolong or stretch the pronunciation of the consonant (t in this case. press "r" to play the audio again). They only exist in the latin transcription, but always result from a "small tsu"-charcter in written Japanese:ka = か, ta = た, so:
"kata" in Japanese looks like this: かた
"katta" in Japanese looks like this: かった

The "っ" in the middle is the small tsu character (here it is next to the large one: つっ). This one is responsible for the prolonged "t". This can also happen for other consonant-based characters, I'll show you more examples.

みんな じゃなかった

私わたし は  幸しあわせ だ

私わたし は エイティーン だ

The “ー” prolongs the “i”. It's an artifact from katakana, a separate Japanese alphabet.