A Conversation with Jon Castelli: On Mix with the Masters, Growth, and the Future of Audio Engineering

Over coffee at Little Ripper in Glassell Park, my friend of 20 years sits forward in his chair, excitedly reflecting on his recent return from Mix With The Masters. There's a subtle but unmistakable shift in his energy – the kind of clarity that comes after a transformative experience. As a mixing engineer behind countless chart-topping records, Jon has always been thoughtful about his impact on the industry, but today's conversation feels different.

Following what Jon calls his "Carlos Alcaraz dropped set" year in 2023, this experience marked a turning point. Like the tennis champion known for losing first sets before sweeping tournaments, Jon emerged from a challenging period with renewed clarity and purpose. In this conversation, he opens up about the power of vulnerability, the evolution of his craft, and what it really means to be a master in today's audio industry.

What made you decide to do Mix with the Masters after being hesitant for so long?

I've always wanted to do it, actually. My hesitation came from not feeling like a "master." It's only been 20 years as of this year - how can one be a master just 20 years into their career?

I know you were particularly concerned about doing video content. Why was that?

There's already so much content of me online discussing my perspectives, and honestly, my work has evolved significantly since then. I'd explain a technique, and people would still think I'm doing that thing, but I've moved on completely. It's like what Peter Attia said about writing a book - by the time you finish it three years later, you're already thinking completely different things.

What ultimately changed your mind?

A few things aligned. First, this was a seminar with no phones allowed in the room - it felt like a full-circle moment that brought together conversations I'd been having with you, Ruairi [O'Flaherty], and people on [The Live with Matt Rad] Discord.

Plus, I've wanted to do seminars since working with Tony Maserati. He'd come back from teaching them saying, "Dude, it was so sick. Wait till you get to do one of these." It had always been a dream.

What did you learn about the Mix with the Masters brand while there?

Talking with Victor and Maxime [the co-founders], I realized I had misunderstood their vision. Even the name "Mix with the Masters" feels almost short-sighted because it's not just about being 50 or 60 with three decades of experience. They want to bring the young generation into the conversation.

How did the format influence your comfort level with sharing?

The intimate setting - 20 people, no phones - created a safe space. As a mixer, I'm always conscious about maintaining the producer's secrets, not exposing things they might want to keep private, but in this environment, people could take notes without broadcasting everything to the internet. Since I'm naturally very open, this format let me speak freely.

It's been two weeks since you returned from Mix with the Masters. What's emerged since our last conversation?

Every time I see people posting photos from the seminar, I get these flashbacks of beautiful moments. The main takeaway was realizing that everyone in that room was a professional - all big fish in their own ponds. We were all the same, and I just happened to be a bit luckier. Yes, I took the risk of leaving Long Island for LA, but so much of it still feels like luck. Everyone there was incredibly talented.

What stood out about the dynamics in the room?

It reminded me of this Billie Eilish interview I saw for KCRW. She talked about looking at the edge of the stage and seeing her fans who've been there since she was 15, now all 22 like her. The sentiment described how she feels as if they are all the same. That's exactly how it felt. These engineers were all the same as me - we all want the same things. Sure, the scale of Billie at Madison Square Garden is different, but in essence, it's not.

How did that manifest in the actual session?

I arrived jet-lagged, opened the door while Teezio was talking, and got this unexpected round of applause. I was thinking, "What is happening?" So I just made a joke about too much compression on Teezio's mix to lighten the mood. That's what it was all about - we were just there to share an experience together.

That's what ultimately sold me on Mix with the Masters - it's not just about you, it's about the connections you make in that room. That's what they've really nailed.

Let's talk about having a point of view as a mix engineer. What did you learn about your own perspective at Mix with the Masters?

It was actually an interesting mirror back because I don't really know my point of view - I'm just doing what I'm doing. Watching the group observe me sprint through a 45-minute mix and then hearing how they perceived what I was doing was revealing.

It's interesting that while you're "in it," you don't think you have a point of view, but others have defined it for you...

Exactly. While I was mixing, the group was surprised by my approach. They kept calling me a producer, and we had this 30-minute discussion where they insisted, "Those are production moves." I had to explain, when I add ambience or transitions, I'm just considering the record's arrangement and how to get through the journey. They see it as producing, but I see it as how an engineer used to engineer records.

How does labeling moves as either "production" or "mixing" affect engineers?

It can box you in unnecessarily. Some mixers believe you shouldn’t add anything to the mix. I believe you should make moves across the board that support the song. That said, someone might be mixing for an artist for the first time. They might be more hesitant to add things, or maybe the song just doesn't need it. That's fair too. Not every song I mix needs “production moves” but I approach each song with that consideration.

How does this play out with new clients? I know you're working on a soul record right now...

I'm doing a pretty heavy lift mix on this soul project - probably my favorite project of the year after Billie. Very different world of music. It's all mono, raw, recorded really well, but I'm mixing it. There's no real rough mix, everything's just up the middle.

I made some moves, and while the band loved most of it, they questioned one delay effect. The artist said, "It sounds like we're going into the territory of feedback on these vocal effects, where I think it could just be like this reference." They wanted classic soul - no tricks, just reverb like you'd have in a live performance. My subtle delay moments were pushing it for them.

It wasn't that it didn't work; it was more like, "Does it need to be there?"

That seems like valuable feedback for shaping the record together.

Absolutely. And what I love is how their notes come as questions: "Hey, I love this, but do you think we can have the Wurli down a dB in this section? Maybe we can have the guitar more exposed to you? What do you think?" It's already collaborative, and that's rare and beautiful.

Michael: I like that; “questions instead of bullet points”.

People often see your highlight reel - working at Tony's studio, then mixing Billie Eilish. But there's a lot of time between those moments. Can we talk about some of the harder times?

This is actually what my Mix with the Masters interview focuses on - my bad year in 2023. I did a lot of work, made good money, but was really unfulfilled by the projects. I was depressed, going through a breakup.

I only wanted to do the interview if I could talk about that difficult year, and they were supportive of that.

I like to call it my Carlos Alcaraz drop set. Alcaraz, one of the best tennis players in the world, often drops the first set of tournaments before sweeping the next sets. That was my 2023 - my drop set. Now I feel like I have three years ahead to crush it.

It seems like there were moments where you considered walking away entirely?

Up until this year, I used to call Nathaniel [my manager] every day saying, "I think I just want to quit. This is hard. How do we keep getting work? The work isn't that good anymore." I was always grateful to be working, but something was missing. Then this year, everything shifted. I called him and said, "My career just started." I haven't thought about quitting once in 2024.

That's such a different story from how people perceive your career trajectory. How do you handle that disconnect?

You need to post the successes - people use that to hire you. It's interesting because at Mix with the Masters, everyone noticed how differently Teezio and I approach Instagram. He does all these videos for brands and gear. I have no loyalty to any gear.

You actually convinced me of the importance of social media. I wasn't even really on Instagram until we decided to try something. It worked, but then I took an 18-month break before coming back to share the Camila Cabello stuff, Billie Eilish stuff, and Omar Apollo. It was just such a big year, I felt like I had to share it.

What's shifted in how you think about sharing success?

What I've realized is that sharing in others' success can be even more meaningful than your own wins. Like today with Ruairi mastering Kendrick Lamar - sure, mixing Kendrick would have been the dream, but being a proud friend, seeing his name flood the internet, that's almost more important to me than my own wins. I just want to listen to the album and celebrate Ruairi.

Instinct seems to be a recurring theme for me and my clients lately. Do you think most people lose touch with their instincts as they get older?

It's never really gone. It just gets tucked away for a lot of people.

I notice many engineers try to follow tutorials exactly, cataloging every move rather than trusting their instincts. How do you approach this balance?

It's interesting because when you watch tutorials or Mix with the Masters videos, people often think, "Okay, this is the right way." They're watching others use their instincts, but instead of developing their own, they're just logging every move like a blueprint. Instinct isn't even in the picture.

Can you give an example of how instinct plays into your mixing process?

Just yesterday on this project, everything was instinct-driven. We had these horns that were mono and centered - not the intended final sound. We kept them grouped together as if they were recorded in the 60s with one microphone, but then put them through a chamber to create space. That wasn't in the rough mix - it was purely instinctual, based on understanding the genre, the era, and how these elements would traditionally be arranged.

That decision seemed to happen instantly for you...

Exactly - I don't even know what happened. I mixed the song in an hour. It wasn't about sitting down and methodically mapping out the record - it was about letting instinct guide the process.

Michael: I was just talking with Justin Glasco about this - he hired his assistant based on the first three questions they asked. When your instinct is strong, it both asks and answers questions in milliseconds. But if you're not asking good questions internally, you won't be able to respond well externally. Taste plays a huge role in this process.

How do instinct and internal questioning relate to each other?

I think people hire us for our taste, which comes from being a historian of what's come before. It's about finding that balance - how do we respect what's happened, exist in the present moment, but also think about where we'll land later?

The key is enjoying the journey. While you shouldn't be overly focused on outcomes when working on art, you still have to recognize that the music will have a life beyond the studio. There will be listeners, and depending on the artist, the stakes can be significant. It's about finding that balance.

Michael: What's at least one thing you've gotten wrong that you've said on record that you want to clear the air about?

Jon: I don't feel strongly against anything I’ve said. I just feel like I was trying stuff out. I would say my whole journey of five years of no compressing made me understand compression more. And when to use it or not to use it. What is it actually doing? Why am I using it? Instead of it being the go-to thing. I think people should experiment with using other forms of dynamic control and then come back to it if they need to.

I do things based on the fact that I say I don't like it. So if I say I don't like something, I force myself to use the tool. I was like, "I hate this R-Bass plugin, I've never used it in my entire career." And I said that at Mix with Masters and I was like, "Fuck, now I have to use it." And I used it. The result was poor. But I tried it and I tried to understand it.

Michael: What's something young mix engineers need to know right now?

Jon: Don't think you're ready to move on to the next level too early. Don't think you're entitled to going out on your own because you’ve spent two years working with a mentor. You might get hired based on a body of work you’ve completed during that time, and that might transition you into that world more quickly, but it doesn’t mean you’re necessarily ready yet.