Barca reached the Champions League quarterfinals after thrashing AC Milan last week.
"Outside of the club there was a lot of doubt, but we were all calm," said Alba.
"We weren't playing badly in these three games against Milan and Real Madrid but we just lacked the same intensity and aggression. The other day we saw the real Barcelona and now we have to maintain this level.
"We have to continue this level of play and aggression until the end of the season."