[Interview] Rob Stenson of CanOpener

by Brian Parker

CanOpener is the impressive new app from audio engineer Devin Kerr and software engineer Rob Stenson, which optimizes the spatial balance, equalization, and sound pressure level for listening to music in headphones. CanOpener uses Kerr and Stenson’s proprietary crossfeed algorithm ,which corrects the discrepancy between listening to music in headphones and listening on loudspeakers.

Music produced on loudspeakers is specifically mixed so that the audio coming from the left and right speakers in a stereo channel are experienced by both ears. However, in headphones, music from the right channel goes only to the right ear, and music from the left channel goes only to the left. This leaves a significant angle of sound out of the mix, without which music lacks a level of depth and wideness. CanOpener’s Crossfeed function allows you to adjust this “wideness” to achieve a more accurate listening experience. Furthermore, CanOpener allows you to pick your headphones (or any other output device) from a list, allowing optimization for specific models.

CanOpener also sports a beautiful equalizer with various presets and spectrogram skins, making the interface both functional and appealing. The app volume is adjusted based on SPL in decibels, rather than Apple’s typical, arbitrary click-and-drag volume slider. An additional feature of CanOpener is the dosimeter, which measures your exposure to sound level over a period of time, meaning you can keep an accurate tab on the safety of your ears during listening sessions.

We had an opportunity to ask Rob Stenson a few questions about CanOpener’s background and functionality, as well as how he and Devin envision the app for the future.

SoundCtrl: When did you develop the concept and prototype of CanOpener? What were your backgrounds before this project?

Rob Stenson: Devin is an audio mastering engineer with a background in sound engineering and psychoacoustics. He developed CanOpener’s core crossfeed algorithm and equalizer as part of his masters thesis on spatial audio processors at the University of Michigan. I’m a software engineer specializing in interfaces, although my background in college was architectural history. Before starting work on CanOpener, I was a software engineer at Twitter, working on the twitter.com interface.

We started work on the iOS version of CanOpener in January of this year, after a mutual friend put us in touch; he realized we had complementary skill-sets, and a shared interest in music (I’m a banjo-player when I’m not writing code). From there we just started widdling away at the app you see now. Here’s a visual history of the app, from the first prototype to the current release.

SC: In the future, do you see CanOpener supporting streaming music apps?

RS: While we do hope to integrate a streaming service — like Rdio, Spotify, or Bandcamp — we’ve been unable to contact those companies to work out licensing deals. We actually have an in-house proof-of-concept that streams directly from Spotify, and it’s a blast to play around with. But, at present, our hands our tied by the various companies API’s and terms-of-service agreements.

SC: Will CanOpener ever function as a mobile device’s complete EQ/audio enhancement system for all of its audio?

RS: We would love to make this happen, but apps on iOS and Android are highly sandboxed, meaning it would be quite difficult (probably impossible without major changes from the device manufacturers) to pull off this level of integration. Something like Audiobus comes close, but that’s more focused on music-making rather than listening. Of course, if Apple did make some changes to their audio system (recent changes in iOS7 hint at this), we would definitely take advantage.

SC: At what stage in the iPhone’s audio chain does CanOpener process sound?

RS: We access audio files in the same way as the stock Music app on iOS, so our app handles everything from reading samples out of a file to passing them directly to the audio output. All of the CanOpener DSP is applied right before we send the samples to the hardware, so it’s the last thing to happen in our audio chain.

SC: Is CanOpener available for both iPhone and Android?

RS: At the moment, CanOpener is iOS-only. We’d love to support Android (and we’ve had quite a few interested customers ask us for an Android version), but a few factors are working against us: Android’s audio system is less sophisticated than iOS’s, and there are so many Android devices out there that we’d have to measure in order to provide the level of quality characteristic of CanOpener on iOS. The major reason though is that we’re only a two-man operation. (Hopefully there are some Android audio programmers reading your post, we’d love to get in touch.) That said, CanOpener is available on Mac OS X as the FHX add-on to the the Fidelia app by Audiofile Engineering.

SC: What are the next stages of updates that you’d like to develop for the app?

RS: We have some very cool in-app purchases planned for 2014, as well as some overdue features (like iPad landscape-orientation support). We’ve also started work on a few other apps, including Speaker+ (currently in beta tests).

CanOpener is currently available on the iTunes App Store for $2.99. Stay tuned to the Good Hertz website for new mobile audio apps, and CanOpener via Twitter @CanOpener.