From Music Hack Day
 CTRL - Interactive Music Installation
Interactive music installation allowing you to add glitchers, delays, filters and reverse effects to any music that can be found on Spotify. All effects are tempo-synced, and a solo-synth is also synced to the key of the song. Also accompanied by a synchronised light-show.
Yuli Levtov, Ragnar Hrafkelsson
 About the hack
CTRL is an interactive music installation allowing you to add effects and synthesizers to any piece of music. By tilting two mobile devices (in this case, iPhones) the user can manipulate the audio easily, intuitively and without the need for prior musical knowledge. By retrieving key and tempo information from Echonest, all the effects are tempo-synced to the track, and (providing Echonest gets the key of the song correct(!)) the solo synthesizer will make even the most unmusical person sound like Hendrix.
 What APIs, tools or kit did you use?
Spotify to stream the audio. Applescript to retrieve title/artist of the current track. Soundflower to route the audio from Spotify to Pure Data. Pure Data to manipulate the audio, using Rjlib and other various Pd abstractions and libraries. Pyechonest to retrieve tempo and key information about the currently playing song. OSC to send tempo/key info to Pure Data. TouchOSC to send OSC data from the iPhones to the laptop. A DMX shield on an Arduino board is used to communicate between Pure Data and a DMX LED lamp.