Trumbo filed at $6.9 million and the D-backs at $5.3 million.
During the hearing, each side uses examples of other players of similar service time as justifications for their salary figure.
The arbitrator must choose one of the two figures, and the two sides can reach an agreement at any point before the arbitrator rules.
"Things are exactly as they were a week ago, two weeks ago, we're in exactly the same place," D-backs general manager Dave Stewart said recently. "There has not been any movement to the positive, so we're still preparing ourselves as if we're going to have to go [to a hearing]."
In his recent role as a player agent, Stewart said he nearly went to an arbitration with two of his players, but in both cases, the teams offered two-year deals that the players accepted.
Teams try to avoid going to hearings if possible, as evidenced by the fact that the last player the D-backs took to a hearing was catcher Damian Miller in 2001.
"I don't think anyone is looking forward to going to an arbitration hearing," Stewart said. "I don't think that the team is, and I don't think that the agent looks forward to the process, and I know that the player doesn't. I've been a player and I know that in that period of time, I wasn't looking forward to going into a room and sitting there listening to a team tell me all the things that I can't do, all of my shortcomings. It's not a good process. It doesn't do anybody any good to go into a room and, I guess, air out your laundry."
Steve Gilbert is a reporter for MLB.com. Read his blog, Inside the D-backs, and follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.