Muse: development case study

Notes, from: “Making Musical Apps with Csound using libpd and csoundapi~” at the 2nd International Csound Conference ­ October 25th-27th, 2013, in Boston.


For about five months in 2013-2104 I worked as a programmer with Boulanger Labs to develop an app called Muse, using the Leap Motion sensor. Leap Motion is a controller that detects hand movement.  Boulanger Labs is a a startup founded by Dr. Richard Boulanger “Dr. B” – to design music apps working with students in the Electronic Production and Design (EPD) department at Berklee College of Music.

Dr. B. was asked by a former student, Brian Transeau (BT), to help develop a music app in conjunction with Leap Motion. The goal was to have something in stores for Christmas – about 2 months from the time we started. BT would design the app and we would code it.

What would the app do? It would let you to improvise music in real time by moving your hands in the air. You would select notes from parallel horizontal grids of cubes – a melody note from the top, a chord from the middle, and a bass note from the bottom.  It would be be beautiful and evolving like “Bloom” by Eno and Chilvers.

Getting started

We bought Leap Motion sensors. We downloaded apps from the Airspace store to learn about the capabilities of the sensor.

One of our favorite apps is “Flocking”. It displays glowing flames to represent fingers. When you move your fingers it causes a school of fish to disperse.

Making prototypes

We started to make prototypes in Max, using the aka.leapmotion external.

This was the first prototype and one of my favorites. It randomly plays Midi notes in proportion to how you move your fingers. It feels responsive.

Mac Os app:

Max code:

Local file: (in Applications)

Does it remind you of any of this?

Design sketches from BT

“So this is an idea of the UI paralaxing. In the background it would be black with say stars. You could see your fingertips in this space and your hand movements would effect perspective changes in the UI. When you touch a cube it would light in 3D space radiating out (represented by the lens flares). This flare or light (like bloom) should continue in the direction you touched the cube. Instead of blocks, these would be grids *like 3D graph paper* subdivided into probably 12-24 cubes.”


Stephen Lamb joined the team as a C++ Open GL programmer, and began exploring the Leap Motion API in Cinder C++.

What kind of gestures can we get to work?

Darwin Grosse, of Cycling 74, sent us a new version of aka.leapmotion that handles predefined gestures, like swipes.

The next prototype was written, in CInder C++. An audio proof of concept. The FM oscillators and feedback delay are written at the sample level, using callbacks. The delay line code was borrowed from Julius O. Smith  at CCRMA:

Delay line code:

Christopher Konopka, sound designer and programmer, joins the team, but won’t be able to work on the project until October.

At this point we are having doubts about the utility of the Leap Motion sensor for musical apps. Because it is camera-based, the positioning of hands is critical. There is no haptic feedback. We are experiencing high rates of false positives as well as untracked gestures.

More prototypes in Max

  • Finger painting
  • Left right hand detection
  • Detecting state changes
  • Defining gestures (air piano)

Reactive Music

Dr. B asks us to consider RJDJ style environmental effects.

This is when we find out that audio input doesn’t work in Cinder. After staying up until about 6 AM, I decide to run a test of libPd in openFrameworks C++. It works within minutes. libPd allows Pd to run inside of C++. By the way, libPd is the platform used by RJDJ.

Programming notes:


We can now write music using Pd, and graphics using OpenGL C++. This changes everything.

What about Csound? It also runs in Pd. Will it run in libPd? Dr. B introduces me to Victor Lazarrini – author of csoundapi~  and we figure out how to compile Csound into the project that evening.

Paul Batchelor joins the team. He is writing generative music in Csound for a senior project at Berklee. Paul and Christopher write a Csound/Pd prototype, in a couple of days – that will form the musical foundation of the app.

We build a prototype using Paul’s generative Csound music and connect it in to Leap Motion in openFrameworks.

Local file: ( in applications)

In this next video, it feels like we are actually making music.

Note: local source code is ofx8 addons leapmotion : leapPdTest5 – but it probably won’t compile because we moved the libs into the proper folders later on

Combining three prototypes:

This was a week of madness. We had essentially three separate apps that needed to be joined: Steve’s Open GL prototype, my libPd prototype, and Paul’s Csound code. So every time Steve changed the graphics – or Paul modified the Csound code – I needed to re-construct the project.

Finally we were able to upload a single branch of the code to Github.

Tweaking the architecture

Steven Yi, programmer and Csound author, helped repair the xCode linking process. We wanted to be able to install the App without asking users to install Csound or Pd. Steven Yi figures out how to do this in a few hours…

Later that day, for various reasons Steve Lamb leaves the project.

I take over the graphics coding – even through I don’t know OpenGL. BT is justifiably getting impatient. I am exhausted.

Redesigning the graphics

Jonathan Heppner, author of AudioGL, joins the team. Jonathan will redo the graphics and essentially take over the design and development of the app in collaboration with Dr. B.

There is an amazing set of conference calls between Leap Motion, BT, Dr.B, and the development team. Leap Motion gives us several design prototypes – to simplify the UI. Dr. B basically rules them out, and we end up going with a Rubik’s cube design suggested by Jonathan. At one point BT gives a classic explanation of isorhythmic overlapping drum loops.

While Jonathan is getting started with the new UI, We forked a version, to allow us to refine the Osc messaging in Pd.

Christopher develops an extensive control structure in Pd that integrates the OpenGL UI with the backend Csound engine.

Christopher and Paul design a series of sample sets, drawing from nature sounds, samples from BT, Csound effects, and organically generated Csound motif’s. The samples for each set need to be pitched and mastered so they will be compatible with each other.

At this point we move steadily forward – there were no more prototypes, except for experiments, like this one: (that did not go over well with the rest of the team :-))

Tom Shani, graphic designer, and Chelsea Southard, interactive media artist, join the team. Tom designs a Web page, screen layouts, logos and icons. Chelsea provides valuable user experience and user interface testing as well as producing video tutorials.

Also, due to NDA’s, development details from this point on are confidential.

We miss the Christmas deadline.

The NAMM show

That brings us up to the NAMM show where BT and Dr. B produce a promotional video and use the App for TV and movie soundtrack cues.


There are more than a few loose ends. The documentation and how-to videos have yet to be completed. There are design and usability issues remaining with the UI.

This has been one of the most exhausting and difficult development projects I have worked on. The pace was accelerated by a series of deadlines. None of the deadlines have been met – but we’re all still hanging in there, somehow. The development process has been chaotic – with flurries of last minute design changes and experiments preceding each of the deadlines. We are all wondering how Dr. B gets by without sleep?

I only hope we can work through the remaining details. The app now makes beautiful sounds and is amazingly robust for its complexity. I think that with simplification of the UI, it will evolve into a cool musical instrument.

In the app store

We scaled back features and added a few new ones including a control panel, a Midi controller interface, a new percussion engine, and sample transposition tweaks. With amazing effort from Christopher, Jonathan, Paul, Chelsea, Tom S., and Dr. B – the app is completed and released!

But why did it get into the Daily Mail?

Leap Motion Midi synth in Max

Midi notes triggered by finger movement


folder: leap-motion

patch: leapfinger2.maxpat

externals and dependencies

Download the aka.leapmotion external – and add it to your Max file path in options | file preferences:


  • plug in a Leap Motion sensor
  • Click the toggle to start reading Leap Motion data
  • Wave your fingers around to play notes

build M4L devices using Max help patches

Edit Max help files to build M4L devices

An audio pitch transposer made from [gizmo~]


folder: gizmo

device: gizmo-mod-example.amxd


  • drag gizmo-mod-example.amxd file into an audio track
  • use dial to pitch-shift audio

Leap Motion version

If you have access to a leap motion sensor, here is the same device using hand gestures to control the pitch.

device: gizmo-thing-700.amxd

externals and dependencies

Uses the aka.leapmotion external – which needs to be in your Max file path. Download from here:


  • plug in a Leap Motion sensor
  • drag gizmo-mod-700.amxd file into an audio track
  • Click the toggle to start reading Leap Motion data
  • Wave your hands around to pitch-shift audio

general suggestions

for converting Max help files to Max for Live devices:

  • Replace UI objects with Live versions. For example, toggle becomes live.toggle
  • Replace audio inputs/outputs with plugin~/plugout~
  • Select UI objects for presentation mode
  • In patch inspector, set the patch to open in presentation mode
  • In UI object inspectors, change default Scripting names to allow automation. “Long Name” is the name used by Live for automation

Leap air piano in Max

Actually in this context, the word ‘piano’ is way too generous. This is a prototype from October, that uses screen mapping to separate left and right hands. It decodes gestures by looking for high velocity downward hand movements. The gestures are mapped to notes and chords based on X position. There is much de-bouncing and tweaking to get results.

Here’s a demonstration which is somewhat painful to listen to, but gets the point across.

local files:

tkzic/max teaching examples/

  • leap-scale-draw5.maxpat
  • leap-sender.maxpat



Leap Motion musical UI for closed eyes

How many musicians do you know that play with their eyes closed? Not many computer music apps allow this. Bloom is an exception.

As an exercise, I tried to make something like Bloom, using Leap Motion. With your eyes closed you can accurately position your hand at the level of eyes, shoulders, hips, etc., And you can quickly move to a point directly outward from your nose, or shoulders. This is the basis of sobriety tests.

The interface, works with a hand motion like sprinkling seeds. Every time you open your hand, it triggers a note based on the height of your hand. It also triggers one of the “Bloom”  circles at the XY position.

The prototype was done in Max/MSP Jitter. It was derived from a “bloom clone” project by John Mayrose at:

Here’s an example:


folder: bloom


  • (main patch) circlething.maxpst
  • (poly~ sub-patch) FMPoly2~.maxpat
  • (Leap Motion main-patch) leap-finger-switch.maxpat
  • (Leap Motion sub-patch) leap-switch-test2.maxpat
externals and dependencies

Note: If you don’t have a Leap Motion sensor, you can use a mouse.

If you are using Leap Motion, download the aka.leapmotion external – and add it to your Max file path in options | file preferences:


(if not using Leap Motion sensor, skip to step 4)

  1. Plug in the Leap Motion sensor.
  2. Open leap-finger-switch.maxpat and click the “start” toggle. 
  3. Wave your hand around – it should be detected and displayed
  4. Open circlething.maxpat
  5. If using mouse, just click in the black “circlething” window to play.
  6. If using Leap Motion, click the message box to activate Leap Motion
  7. Then open and close your hand, over the sensor to play
  8. High notes are higher in the window.

Leap Motion example using Cinder and c++ audio

This is a prototype from October – just getting around to posting it.

The hand position (x,y,z) is sensed by LeapMotion to control parameters of an FM synth with feedback delay written in Cinder audio (c++). The graphics were adapted from a Cinder LeapMotion demo.

Local source is in: cinder/cinder_dev/blocks/Cinder-LeapSdk/samples/LeapApp/xcode/LeapAppTZ2.xcodeproj

Uses cinder Leap demo code combined with simple audio synthesis using callbacks in c++