The Melody Triangle mobile app was developed for the Android operating system, it was launched on March 30th 2013, and is available as a free download from the Google Play app store12. It follows the same principles as the desktop version of the application, with the triangle the main interface element, and three tokens, that each generates a melody when placed in the triangle. An annotated screenshot of the interface is provided in fig. 3.9
When the app is first launched after install, a walk-through tutorial is provided, where each interface element in turn is highlighted and its function described with an on-screen text pop-up. At launch the three tokens, each of slightly different colours, are placed in slots on the top left of the screen. From there the user drags a token into the triangle. Once in the triangle, the melody gets generated automatically, and the vacated slot where the token was becomes a ‘cog’ icon that the user can press to adjust parameters specific to this token, or voice.
There are two global settings that the user can adjust. On the lower left, the plus and mi- nus buttons let the user adjust the global tempo. On the right, the pressing the icon that looks like a spanner allows the user to select between three musical scales - pentatonic, diatonic and harmonic. In pentatonic mode, the transition matrices would have 6 symbols, and in diatonic or
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Figure 3.10: Screenshot of the menu for token/voice specific settings.
harmonic mode, 8 symbols (covering the notes of the scale).
Every time a token is moved, it is mapped to a new Markov transition matrix. Additionally a new mapping from generated symbols to sound samples is generated. The mapping was a one- to-many mapping, where different symbols could be mapped to the same note, and additionally a symbol can be assigned to a ‘rest’. It is recognised that these design decisions would potentially add some noise to an analysis, however it was deemed they greatly increased the quality of the musical sequences. This would make the app be more able to sustain user engagement, a matter of critical importance in all crowdsourcing projects.
Each token can be one of three instruments, piano, bass and drums. The tokens are marked with a P, B, or D to correspond to the current instrument selection. Whenever a user touches the ‘cog’ icon that corresponds to a voice, a pop-up menu appears, allowing the user to adjust voice specific parameters. A screen shot of this menu is provided in fig. 3.10.
From there a user can change what instrument the voice is mapped to, the register of the instrument, and how many notes per-beat the voice should generate, if the token should go onto the off-beat, and a volume specific to this voice. There are three registers for the piano (high, medium, low), two for bass (high, low), and none for the drums13. As such a wide array of features is provided, allowing for a large gamut of possible musical outputs.
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Table 3.2 shows the default settings of the app. These were chosen to help ensure as imme- diate an engagement as possible. For instance it was noted how some users of prototype versions of the app who would drag a ‘bass’ token into the triangle, but as users often would not have headphones on, the sound heard would be very quiet. As such it was decided to not have bass be one of the default instruments.
Table 3.2: Default settings of the Melody Triangle mobile app
Global BPM 90
Scale Harmonic
Token 1 Piano, high register, two notes per beat Token 2 Piano, middle register, one note per beat Token 3 Drums, two notes per beat
Data Collection
The heart shaped ‘like’ button at the right hand side of the interface is the means by which users would submit their settings. Whenever it was pressed, a snapshot of the current state of the app would be taken, and uploaded to a central server. The ‘like’ button was pointed out during the initial walk-through tutorial, and users would be periodically reminded of it while playing with the app. It is these submitted settings that will be analysed in the following section.
Each submitted setting (or ‘song’) is given a unique id. This id can be entered by any user of the app to download another user’s submitted settings. This feature is available through the button with the ‘cloud’ icon.
This is also the access point to the Melody Triangle Radio, which allows users to listen to other users’ submitted settings easily. Upon entering ‘radio’ mode, the app queries the server for a randomly selected submission (or ‘song’), and sets the app to these settings. Additionally, a new icon appears on screen, a ‘next’ button. Whenever the ‘next’ button is pressed, another randomly selected song is downloaded and played back on the phone.
In this mode the user can quickly sample many submissions from other users. The app notifies the user that if they enjoy what they hear, they can press the ‘like’ button. This is then registered on the server, and the settings accumulate a ranking, forming a music chart, tracking the most popular songs. The chart was displayed on the web-site associated with the project14. Recordings of the five most popular songs are provided in the supplementary materials accompanying this thesis.
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Making this app was very challenging, in particular with regards to getting reasonable per- formance out of Android’s audio libraries. The next section details how this was achieved.