For most re-recording mixers, the most challenging scenes to mix are the ones with lots of action and requires a multitude of sound effects. For re-recording mixer, Tom Fleischman, it’s the opposite. He has been working with director Martin Scorsese since the ’80s. The two first met when Fleischman was a freshman at NYU and Scorsese was teaching film. They worked together later first on “Raging Bull” and then on “King of Comedy.”

Since then, Fleischman has continued to work with the director. Their most recent collaboration is on “The Irishman.” His main objective with the epic was to work on the sound, or rather quiet the sound so the viewer doesn’t get distracted from the performances. To both Scorsese and Thelma Schoonmaker, that was the most important thing, keeping the performances strong and intimate.

Fleishman explains the process below and discusses his relationship with Scorsese.

You and Marty go way back. How did that relationship begin?

I first met Marty when I was in college during my freshman year at NYU film school. He was an instructor there teaching a film history course.

I didn’t finish NYU; I left and worked at a sound studio, but it wasn’t until after a number of years later that I started working with Marty. I did temp mixing on “Raging Bull.” That was with Thelma Schoonmaker.

On the next film, “King of Comedy,” that was the first time we worked together. I was a second mixer there. Dick Vorisek was the lead mixer on that. But Dick had some health problems and he couldn’t work all the time. Marty liked working long hours. I would stay and work in the evening with Marty, and that’s when we started working together.

How has technology has evolved in the world of sound mixing from then to “The Irishman?”

In ’84 when I started working, everything was analog. It was a more cumbersome process back in those days. The tracks were simpler. You couldn’t run as many tracks. With digital technology, everything changed. There was a period in-between where we were working part digital and part analog, we still had to make the tracks.

Everything now is digital and it’s all on the computer. There’s a big change in the tools that we use, but the process hasn’t changed all that much.

We still have to go through it scene by scene and make sure the dialogue plays properly. We mixed the music and the sound effects making sure everything works the way it should. That part of the process really hasn’t changed much, it’s just the tools and the medium. Instead of magnetic film, we’re using computers. The process is a matter of getting the dialogue sounding good.

With Scorsese, it’s about keeping the performances without affecting the signal processing. We don’t want to make the track too clean, what winds up happening is it affects the quality of the voice. He’s most keyed into the performance. It was particularly true of “The Irishman.” Most of the movie is quiet and intimate, and that was what he was most interested in. He wanted to keep the quiet scenes as intimate and keep those performances as pure as possible because that’s where the heart of the scene is.

The looks between the characters and their tone, you didn’t want to distract from that in any way with background sound effects. In some cases, there was music playing, but in many cases, most scenes were played without music.

That becomes a very challenging thing for a mixer. It’s often said that big action sequences with lots of sound effects are the hardest things to mix. I find a quiet intimate dialog scene between two people in a quiet room where you might have environmental problems on the set that creates noise to be the most difficult type of things to mix. Dialog mix is ultimately the most important part of the process for me.

There are several scenes that use silence — how does that come into play when it comes to sound mixing?

It’s the morning scene at Howard Johnson’s when Pesci tells him that he has to go to Detroit to do this thing. It was almost the most challenging thing in the whole movie. There were problems on the set with noise. That was the most important scene in the movie to Thelma and Marty. We could not lose the intimacy between the two characters and what was happening. Emotionally, when he’s telling him, he has to kill his best friend. Thelma really pushed us on that scene to get it quiet. There were noise problems on the set, and we had to quiet it down, but we couldn’t affect the quality of the voices. That was a tricky thing to get right.

There’s a quiet dialog scene in the beginning where Keitel and Pesci are talking about blowing up the laundry. There was no music and it was in this quiet restaurant. There was a bartender in the background. Ray and Bobby are in the background too in a booth, and we didn’t want to hear those sounds. We found the sounds of traffic were filtering in.

There was nothing to cover the production track — which is the sound recorded on set. We had to quieten it down a little bit.

There was another scene with De Niro in his pj’s and that was another scene we tried to quieten down. All those scenes were the most important to Marty and Thelma because they were the most intimate. The performances there were really strong and I didn’t want to hurt any of those performances.

How long is the process?

That scene isn’t a long one, but we had to go through it a number of times. We didn’t get it right until the third or fourth try. We spent a total of two days just mixing that scene.

Who is in your mixing room?

The way we approach this is I’ll usually sit with Phil Stockton and put a scene or reel together. I work in ten or 15 minute reels. Thelma will come in, and we’ll work to refine that. She’s got a very good sense of what Marty wants because they’ve been working together for months. She knows what he’s looking for, and she’ll guide us. Thelma will refine it to the point where it’s sensible to him. He’ll come in and review it and make it his. That’s how our process has worked for many years.