Enabling everyone to remix anything

Three and a half years ago, I downloaded a turntable app on my way to class. I had never DJed before in my life.

Last month I performed on stage in front of thousands using Crossfader, a free iPhone app I’ve developed with the rest of the company formerly know as DJZ.

16 months after the launch of its first version, Crossfader 4 went live in the app store today. Like our Crossfader community and the DJZ team itself, Crossfader 4 is greater than the sum of its parts. But before core features like Radio, Friends, and Packs became integral components of Crossfader, it was just a simple—the simplest—DJ app.

My journey developing that initial, minimum viable product began years earlier on three separate prototypes that helped shape what Crossfader would and wouldn’t become. Those prototypes were: Audio Butcher, SoundCrate, and DJZ/U.


I downloaded my first turntable app on my way to Mobile Music, instructed by Professor Ge Wang at at Stanford’s Center for Computer Research in Music and Acoustics (CCRMA). That winter, I recruited Electrical Engineering Ph. D. candidate and turntablism aficionado Hyung-Suk Kim to work together on the class’s final project. Neither of us had made mobile apps before, but together we created Audio Butcher in just a few weeks:

Audio Butcher demo, March, 2011

Though we gave countless well-receieved demos around campus, Audio Butcher, developed March, 2011, was never released. Bare bones as it was, it viscerally and emphatically stated the case for a simpler mobile DJ app than anything that was currently on the App Store.

All that we felt was missing to make a truly revolutionary app—besides iterative features like beat-matching and more audio effects—were a social network and an instruction manual.


Rather than build our own social network, Hyung-Suk and I desired to leverage SoundCloud as a network for finding songs to remix and publishing those remixes, thereby creating a recursive engagement loop for our users. While we built SoundCloud integration into Audio Butcher, we sought to launch a more fully realized product with less requirements first. The result was SoundCrate, an innovative SoundCloud music player and discovery app:

SoundCrate v1.0 demo, March, 2012

We shipped two complete iterations of SoundCrate between 2012 and 2013, teaching ourselves mobile UI/UX design by trial-and-error while studying for school and taking on internships on the side.

Having interned at TuneIn (formally RadioTime), and seeing how they acquired their #1 3rd party app, I was encouraged at the prospect of building a better client for SoundCloud. Unfortunately, SoundCloud was not the ideal platform to build a third-party app for (though perhaps not as bad as Twitter). In 2013 SoundCloud shuttered their developer forums. When SoundCloud rolled out massive upgrades to their site and their own app they kept the API’s for these new features private for over a year. More than two years later, SoundCloud finally released an iPhone app that was tailored for listeners rather than uploaders, like SoundCrate was years before.

SoundCrate v2.0 screenshots, March, 2013


As I finished SoundCrate 2.0, my friend, CCRMA classmate and DJZ co-founder Gina Collechia introduced me to Devin Chalmers, another co-founder whose work on KCRW’s Music Mine I admired. After hearing about the talented team at DJZ, I took an indefinite leave of absence from school to work on a project known at the time as DJZ/U.

DJZ/U (as in University) began with the mission to educate the next generation of DJs:

DJZ is developing an iPhone app that teaches music fans how to DJ through a series of 10 interactive lessons. After completing lessons, the same app is used to perform live DJ sets. It teaches them the basics of DJing, supplies killer songs to start with, and then evolves with the user as their skills progress.
(co-founder Andy Chimicles to co-founder & CEO Seth Goldstein, December, 2012)

DJZ/U’s design called for new elements to be added to the interface with each stage the user completed—until the user had a “complete” set of DJ tools at their fingertips. But it seemed that every interface element detracted from the overall experience until the interface was a cluttered, confusing mess.

DJZ/U early prototype, January 2013

Backstage at Ruby Skye one night in San Francisco, Seth, Devin, Gina and I got to talking. What if we used the device’s sophisticated sensors to control the music?

The conversation reminded me of my advisor Ge at CCRMA. In 2008, Ge created Smule’s Ocarina, the iPhone’s first hit music app, which simultaneously turned the device into a flute-like instrument and its users into musicians.

Using the iPhone’s gyroscope and accelerometer to move the crossfader and control effects not only allowed us to win back precious UI screen real estate but allowed us to create something more than either just a tool or a toy: an instrument.

Crossfader prototype, February, 2013

Reducing the number of elements one-by-one compelled us to innovate in other ways, too. We needed a way to load songs so that the best parts always played in sync. The ingenious solution devised by co-founder Jake Lamante was to phrase-match 16-bar loops (previews for full songs), making it that much more certain that our users would always sound awesome.

We knew we were done stripping down the UI when there was only one thing remaining on the screen: the Crossfader.

Crossfader promo video, April, 2013

Finally, in April 2013, Crossfader was ready for its app store debut.


The Global Remix Community

Crossfader 1.0 was the beginning of something bigger than just a DJ app... Sine then our DJ app has fostered the world’s greatest remix community. I can hardly begin to summarize the contributions by the talented DJZ team that have made this possible. Some of the key features we’ve launched over the past year include:

  • Dynamic tempo-stretching and harmonic pitch-shifting (October, 2013)
  • Social networking (March, 2014)
  • User-generated remix radio (June, 2014)
  • Daily updates featuring the hottest new music

Today, Crossfader does more than just enable everyone to sound awesome remixing anything; Crossfader is the perfect soundtrack to your party or workout, a fun way to rediscover your favorite songs alongside your new favorites, and the best way to share mashups with both friends and strangers around the world—whether you are an aspiring DJ/producer,dance music fanatics, or a casual music listener.

If you haven’t downloaded it yet, what are you waiting for? (it’s free!)

DJing with Crossfader at Oysterfest at Golden Gate Park in San Francisco, May, 2014