Two seconds.

That’s how much time Georgia Tech defensive coordinator Ted Roof estimates he will have to examine down and distance, consider personnel and remember tendencies to decide on a play to send in when the Yellow Jackets play North Carolina on Saturday in Chapel Hill, N.C.

It’s not a lot of time, but that may not be a bad thing.

Frustrated with the defense the past few games, coach Paul Johnson said he wants the calls simplified .

“You can’t be doing stuff that you’ve got to have all kinds of communication involved,” Johnson said. “Pretty simple — you’ve got to have some hand signals and then if you’re relying on things to change (the call) four times before the ball’s snapped, you’re going to have problems.

“I don’t care if you play in a quiet room. You’ve got to make a call and play it.”

This desire to simplify the defense and systems isn’t new.

Johnson referenced issues with communication and an inability to get lined up in 2012 after terminating Al Groh as defensive coordinator: “The communication part wasn’t transcending to the field; we were having a hard time getting lined up,” he said after firing Groh because the Jackets gave up an average of 46 points and 573.3 yards, with opponents converting 31 of 46 third downs in losses to Miami, Middle Tennessee State and Clemson.

In last week’s 38-35 win over Duke — a game in which the Jackets led 28-7 at halftime — Tech was called for a substitution infraction when it had 12 men on the field on second-and-goal at the 1-yard line in third quarter. After the teams lined up, Johnson had to call a timeout because Duke had a wide receiver standing open and alone near the right hashmark.

Those were only two examples. Duke scored a touchdown later in the game when safety Corey Griffin was busy trying to get two players who had lined up incorrectly into their correct places. Focusing on that, Griffin didn’t notice the tight end he was supposed to cover slip through the line and into the end zone, where he caught a pass that gave the Blue Devils a 35-31 lead with 8:55 remaining.

“Everybody’s got to have an idea of what everyone else is doing,” Johnson said. “You’ve got to limit the mistakes and the alignment errors and those kind of things. If you’re still having them this late in the year, you’ve got to cut back on what you’re doing. You can have the best plans in the world, but if the guys on the field can’t get it, then it’s not going to be good.”

Tech’s defense hasn’t reached the depths of 2012. This season, it is allowing averages of 23.5 points and 386.4 yards per game. But there are similarities to 2012: Opponents are converting 51 percent of their third downs (128th of 128 FBS teams), and the Jackets aren’t effective at creating pressure (eight sacks, 122nd in FBS) or turnovers (nine, T-101st).

They likely will need to improve in all areas against North Carolina, which has one of most efficient offenses in the ACC, if not all of the FBS.

The Tar Heels’ offense still averages 32.5 points and 437.6 yards despite running the third fewest plays (542) in the ACC and having the lowest average time of possession (24:37). It averages 6.5 yards per play, second only to Louisville’s 7.8. It helps that the Tar Heels lead in the ACC in third-down conversion percentage (47.7).

The speed at which the Tar Heels will play cuts down on the time the defensive players get to try to recognize formations, which helps them read their keys. Roof said the worst look in the world is to glance down from the press box and see players looking at the sideline with palms raised, wondering what they are supposed to do.

So, Roof knows that he has got to be decisive and keep things simple, but sound.

Two seconds isn’t a lot of time.

Safety A.J. Gray said that because of the speed at which the Tar Heels move from one play to the next — “it’s almost like they already know the play they’re running,” he said — there won’t be time for the defense to shift out of the original call from the sideline. North Carolina can push the pace as fast as perhaps any team in the country, often running to the line of scrimmage to start the next play. On one play in their win over Florida State on Oct. 1, the Tar Heels completed a 33-yard pass, and despite the distance the team needed to cover to get to the new line of scrimmage, snapped the ball 12 seconds after the previous play was whistled dead.

Gray said that players will look to the sideline for the play call and won’t check out.

“We’ll call the signal and go with it,” he said.