## 4. Actively Augmenting Mobile Devices
### Active Augmentation Framework
#### 5.2.3 Example: Marimba Physical Model Using FPML and mesh2 faust
More examples of models created using this technique can be found on-line (Faust Physical Modeling Toolkit Webpage: [[https://ccrma.stanford.edu/~rmichon/pmFaust/](https://ccrma.stanford.edu/~rmichon/pmFaust/)]([https://ccrma.stanford.edu/~rmichon/pmFaust/](https://ccrma.stanford.edu/~rmichon/pmFaust/))). ### Discussion and Future Directions

The framework presented in this section remains limited by several factors. Audio latency induced by ADCs and DACs prevents in some cases the implementation of cohesive bidirectional chains between physical and virtual elements. Audio latency reduction has been an ongoing research topic for many years and more work has to be done in this direction. This problem is exacerbated by the use of mobile devices at the heart of these systems that are far from being specialized for this specific type of application (i.e., operating system optimizations inducing extra latency, number of analog inputs and outputs, etc.). On the other hand, we believe that despite the compromises that they entail, mobile devices remain a versatile, and yet easy to customize platform well suited to implement hybrid instruments (e.g., the BladeAxe[42]). The Faust Physical Modeling Library is far from being exhaustive and many models and instruments could be added to it. We believe that mesh2 faust will help enlarge the set of functions available in this system. The framework presented in Section 5.2.1 allows us to assemble the different parts of instrument models in a simple way by introducing a bidirectional block diagram algebra to Faust. While it provides a high level approach to physical modeling, Faust is not able to generate the corresponding block diagram in a structured way. This would be a nice feature to add. Similarly, we would like to extend the idea of being able to make multidimensional block diagrams in Faust by adding new primitives to the language. More generally, we hope to make more instruments using this framework and use them on stage for live performance. ## 6 Conclusions

By combining physical and virtual elements, hybrid instruments are \"physically coherent\" by nature and allow instrument designers to play to the strengths of both acoustical and digital elements. Current technologies and techniques allow us to blur the boundary between the physical and the virtual world enabling musical instrument designers to treat instrument parts in a multidimensional way. The Faust Physical Modeling Toolkit presented in Section 5 facilitates the design of such instruments by providing a way to approach physical modeling of musical instruments at a very high level. Mobile devices combined with physical passive or active augmentations are well suited to implement hybrid instruments. Their built-in sensors, standalone aspect, and computational capabilities are the core elements required to implement the virtual portion of hybrid instruments. faust2 smartkeyb facilitates the design of mobile apps using elements from the Faust Physical Modeling Library, implementing skill transfer, and serving as the glue between the various parts of the instrument. Mobile devices might limit the scope of hybrid instruments by scaling down the number of connections between acoustical and digital elements because of technical limitations. However, we demonstrated that a wide range of instruments can still be implemented using this type of system. The framework presented in this paper is a toolkit for musical instrument designers. By facilitating skill transfer, it can help accelerate the learning process of instruments made with it. However, musical instruments remain a tool controlled by the performer. Having a well designed instrument leveraging some of the concepts presented here doesn't mean that it will systematically play beautiful music and generate pleasing sounds: this is mostly up to the performer. We believe that mobile hybrid instruments presented in this paper help reconcile the haptic, the physical, and the virtual, partially solving some of the flaws of DMIs depicted by [PERSON] (2008).