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Interview With Rej Of Caustic

Updated: Nov 27, 2022

Interview With Rej Of Caustic

Interview With Rej Of Caustic features my discussion with the creator of one of my favorite phone apps for music creation. At the time of conducting this interview this site was brand new and I was way out my league. Enjoy watching me fumble over everything I say, while Rej is super freaking cool about it!

Interview With Rej Of Caustic

Excited To Be Having This Interview, Rej!

I’d like to thank you for taking the time to field some questions from me. Caustic is a marvel of an application, if I may compliment you first. As any readers of this site know, I am a massive advocate for your brainchild DAW. I’m also pretty sure my secretly hates you, Rej, because Caustic is what first flipped my personal switch towards using synthesizers in my own material. Now, it has become a full-blown obsession and the poor woman has sacrificed her entire kitchen table in order to house all my gear (thank you, Katie :)).


8/23/2020 – FYI – It is now a 6 foot wide, full workstation desk, sporting drawers and all those Bells and Whistles, even. Imagine that! Now I take up 3/4’s of the Kitchen.

My Introduction To Caustic

I recall a friend once saying to me, “Yeah man, I sort of just showed you this app and you took it and ran with it.” He’s definitely not wrong. I am a longtime fan and supporter of Caustic, SingleCellSoftware and yourself – With that, let’s get this show on the road!

Which Were You First, A Musician Or A Programmer?

A “musician” first I guess, but it’s not like I’m really good at any particular instrument. I learned to play piano by ear when I was young, maybe 6-7. We had an old electric organ lying around and I learned to play things like “Mary Had a Little Lamb,” etc.

My Mom Heard

This and signed me up for piano lessons. I did classical piano until I was 12-13 when the lure of the electric guitar took over. Played some metal, lots of grunge and a bit of folk back in my teens but then gave up playing for a while to focus on a programming degree.

When did you first realize the opportunities open to you by combining the two skills?

I had always loved making software tools for creative people, but mostly this took the form of animation tools for various video game companies. The last place I worked at asked me to revamp the audio engine and that was the first time I had a crack at sound programming.

I Really Enjoyed It

And working with audio people but unfortunately the studio closed down a few months after that. This was during the rise of mobile apps so I decided to take a leap in that direction.

How long have you been working at each craft?

I’ve been playing music on and off for most of my life, and programming since I was about 20. I’m 42 now so you can do the math.

Where did the idea of creating such a robust DAW even come from? Why not a desktop softsynth like VCV Rack?

Hehe, you might not say “robust” if you tried Caustic 1.0. To be honest the whole thing was an experiment. An experiment to see if I could create a synthesizer – I had only written a few simple effects at that point – and mostly an experiment to see if there was even a market for a music app on Android from a no-name developer.

At this point in time

iOS was pretty much the only game in town as there were only a handful of simple music making apps on Android, and none from the big guys. The desktop market was even more saturated and more dominated by huge players. Add to that the mess that comes from different PC hardware, configurations, drivers, etc…. No thanks, not the place to start.

You wrote all the code for Caustic yourself?

Mostly. I mean some bits I got from people sharing code fragments online. Usually just pseudo-code, which kind of like saying how an effect or generator works but not actually giving the code out.

How long did it take you to build, beginning stages through launch?

At first, it was just a simple subtractive synth, to test out these concepts I was learning like waveform generators, filters, envelopes, and basic effects. I toyed around for a many months putting things together until I finally decided to wrap it up in a user interface and add some sequencing so you could actually compose with it.

Things went pretty quickly after that and because no one had any expectations, I launched on the Android Market (as it was known then) without much fanfare.

How many times did you think you were done, only to find that one dang glitch that you thought you’d cleared away?

One of the things I learned from the video game industry is that there’s always one last bug, but at some point, they get so obscure and hard to reproduce that you have to call it and just release.

If You Tried To Get Rid Of Every Bug

Nothing would ever get released. It sounds a bit dirty to say you’re knowingly releasing something with “known issues” but that’s what you have to do. There are of course show-stoppers. Usually anything that means people lose their work. You can’t, in good conscience, release any software with things like that.

Interview With Rej Of Caustic

I have to be honest before continuing on, Rej. My love of your software left me, for the first time interviewing anyone for this site.. intimidated. I was reassured over and over that you’re an awesome and open guy. That I never doubted.

The intimidation manifested more in the form of a bit of writer’s block. SO, at that point I took to the streets. After making a somewhat quick post on Reddit I discovered that you have many fans out there who feel the same as I do, that you and your work has changed our life.

They were happy to offer up some ideas and I feel obliged to credit them the best I can –

From Redditor u/Trepki –

What were the biggest challenges you faced while you were making the app, your biggest regrets, and the best thing that happened because of the app?

I mean, I was learning as I go so there were lots of challenges, and some of the ways I engineer things now block me from doing other things, so there’s a bit of regret there. The best thing that has happened is that a community of users grew around the app; power users, musicians, other programmers. Each playing their part, finding a way to share their experience with others and help out.

From Redditor u/joeyc1123 –

This user was wondering whether a standalone version of some of the instruments inside the Caustic app were ever given consideration for a physical standalone synthesizer (piqued my interest too)?

Certainly, it actually happened a few months ago! I didn’t post much about it because it tends to attract a lot of negative commentary along the lines of, “Why are you wasting your time on this? Where’s Caustic 4!?”

You can read more about it here:

But yeah, it was something that’s been on my mind for awhile and a successful first attempt I’d say. I’d REALLY like to make a modular that uses the same hybrid digital code/analog control model with bits from Caustic, but that’s probably not going to happen anytime soon.

Now I really liked this next one . .

From Redditor u/kdjfsk –

To your knowledge, what’s the most commercially successful music made using Caustic? – Be it a single, an album, game soundtrack – What is the tune and how did its success make you feel?

I don’t know… There’s been a few people who have written me to say they’ve used Caustic-created music in their indie film and things like that but I don’t think I’ve ever heard of Caustic music being used in anything big. I mean, when people contact me, it’s usually to ask for things (features, support, etc), so I don’t hear much of where people are using their tracks sadly.

And, finally, both u/Dawiz95 and I agree that we just want to know a bit more about the Genesis of the app.

What are some things or interesting tidbits/factoids that no one knows about from creating the app that would make us stop and say, “Hmmmm, I did not know that!” ?

The story of how the app got its name is an interesting one. Like most projects, it didn’t have a name for a long time. Its code name was “NoGoodReason” because of the similarity to a certain other audio package I respect and the fact that mine wasn’t exactly awesome at first.


At some point I had a synth going (early subsynth), a drum sampler (beatbox) and a pattern sequencer. So it was pretty fun, you could make little melodic, rhythmic loops. I was constantly showing it to a work mate of mine who made electronic music.

One Day

I got some 303 emulation code working so I added this to the package and we both played for hours with it, it was finally fun. He said something along the lines of, “You’ve got a nice little app for making acid tracks, you should name it something that has to do with “acid”. What are chemical words like acid? Alkali? well, that’s the opposite of acid so, no. Corrosive?


I Had Only Set Out A Bit Of Room

In the UI for the app’s name and needed something short: “Caustic” was perfect. Also, I think someone on your reddit thread already linked this but there are a few early prototype screenshots on Musical Android that folks might find funny.

Being From A Video Game Background

I like to hide Easter eggs in my apps. I don’t think the current version of Caustic has anything hidden anymore, and I never got around to finishing the next egg, but I like doing that kind of stuff and hinting at how people can find them.

There’s one in my recently-released Mastering app, but I haven’t told anyone how to get to it yet…

That’ll Come Soon 🙂

That’s the creme de la creme of questions received, so I thank all contributing fellow Redditors for replying to my post and I hope I did your questions justice!

At this point, the hesitation started to cede a little and I got to writing once more . .

At Any Point

Did you utilize the services of a third party? Someone for let’s say Marketing, or Logo Design? Or, is/was everything entirely yourself?

The current logo was something that was sent in by a user a long time ago. I don’t think any money changed hands. It was just a guy who enjoyed making logos. He, then, helped out a guy who likes making audio tools but isn’t exactly an artist.

The Concept Was Mine Though

And was meant to represent a benzene ring. I remember that shape from organic chem class and I always thought it was evocative.

Any other music applications out there that excite you? Ones that pique your interest and you can’t wait to see where they go?

There’s some super-creative stuff coming out on iPad every week it seems, so it’s hard to keep up. I have a soft spot for the other Android indies I’ve spoken to via email and their apps. Early on there were pretty much only two decent music apps on Android: Electrum and RD3.

I Got To Communicating

Via email with the dev from Electrum and he helped me out with getting started. Since then I’ve spoken to other devs like Andreas who makes G-Stomper. We exchange questions, code and frustrations.

What do you have installed on your phone right now for music production?

Hmm, I just changed phones so not much installed apart from my own apps. I don’t really make much music anyway.

I Just Like To Make Little Grooves

How did you manage to land a deal with Korg to be pretty much one of two apps (that I know of) that can be utilized to import samples to the Volca Sample? What was the process like to obtain their blessing?

No Blessing Required

It was (and still is) an open-source SDK that Korg provides. Anyone can use it and make a compatible app. I made mine on a whim when I heard about this SDK, thinking I already had everything I needed with my audio editor. After releasing it, I did receive contact from people at Korg, including the device’s lead engineer, to thank me for helping to open things up to Android and other platforms. I do think there are more compatible apps now though, just not listed on their website.

Your last update to Caustic (to my knowledge) was the inclusion of the SawSynth. For dorks like myself, please tell us there’s more on the horizon with Caustic… Is there any planned update scheduled?

I know this is going to make a lot of people angry: There is an update coming up, but apart from a few bug fixes and performance enhancements, it won’t change much.

You See

Google is forcing everyone to update their native apps to 64bit in August or get pulled from the Play store. We’ve had plenty of heads up, I’ve just been putting it off, hoping I could bundle it with bigger changes, but it looks like I’ve run out of time and need to update now.

After That

I guess the main thing people ask for is to remove limits on the number of machines and effects, so that will probably be the main focus of the next proper update.

What other apps out there which I may have knowledge about have you been a part of?

I’ve never worked on any other mobile apps apart from my own stuff. I ported and tweaked a little falling sand game as a nostalgic tribute to the original and as a programming exercise in optimization.

Before All This

I was at BioWare and worked on Mass Effect 1. A lot of people have either played or heard about that one. Different deal though, we were ~250 people on that project so I played a very small part.

When people tell you that they are users of Caustic, or that it has had a significant impact upon their growth as an artist do you take sort of a Bob Moog outlook on it? As in, I just want to hand you the hammer, you build the house? Or, what sort of emotion comes over you when presented with such flattery? Is it something that you ever anticipated fielding questions on during the initial build?

Well, to this day I’ve only ever met one person in real life who regularly uses Caustic so not much to go by (and certainly not in the same camp as Moog), but yes I get really excited when I see what talented people make with my little tool.

I’ve Had To Call Bullshit

And ask to see project files from a few people because I was completely blown away with what they were producing.

Any words of wisdom for folks out there who have affinities towards both Music and Programming looking to expand their horizons?

It’s actually hard. There’s not much out there to get started. Lots on music and lots on programming but not both together. There is quite a lot of advanced discussion about audio programming but making that first leap isn’t easy.

I’d Say If You’re Going

To program audio, learn a low-level programming language and play around with the basic concepts of making sounds, filtering and effects, then experiment. Make an instrument you would want to use.

Rej Out!

That concludes this interview with Rej, creator of the wonderful tool Caustic. I genuinely learned a lot from this chat. Things I would have never known had Rej not been kind enough to reply to my request for an interview. It’s very interesting to see your assumptions about things washed entirely away by going directly to the source. What a novel notion!

Either Way

Please be sure to support Caustic by downloading it. In my opinion, it’s the best ten bucks you’ll ever toss at your phone. I’d like to thank Rej once more for taking time out to answer my questions and, as always, keep on rockin’ and rollin’!

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