When preparing to use the Rhythm Tracks for NWC App on a Mac, a virtual MIDI synthesizer is also needed before you can hear the pattern loops during play back. In order to create the virtual synthesizer, you will need a program called AU Lab.
We have created a new web application that can be used to create rhythm tracks for use in NoteWorthy Composer. This application utilizes the features introduced by the working draft of the Web MIDI API. At the time of this writing (May 2014), the MIDI features are only available in the latest version of the Google Chrome browser, and require some manual tweaking to get things fully enabled in the browser. Once your browser MIDI setup is working, you can use the new app to create new rhythm patterns, export them to NoteWorthy Composer, and share them with others via a simple web link.