Roger B. Dannenberg
STATUS: Basic framework is complete, simple demo now runs, needs much more work to define and build out a library of unit generators.
Arco is a sound synthesis engine that offers dynamic patching of
of unit generators. It is designed to operate as a small embedded
server, running either in its own process or within an application.
In the spirit of "smaller is better," Arco DSP is mainly delegated
to FAUST, leveraging a wide range of existing algorithms. Arco
control is delegated to external languages connecting through O2,
which supports running Arco within the same application, in a
separate process or even on a remote networked host.
Arco should be a nice alternative to libpd as an embedded sound
engine. The author is mainly using Arco in tandem with Serpent,
a real-time Python-like scripting language, but other language
bindings are possible.
If you are familiar with other computer music sound synthesis systems, it may be useful to know how Arco is differs. Some of the distictive features of Arco are:
- Embeddedness. The main application envisioned is adding a flexible sound synthesis capability to an application or existing programming language. This calls for a small footprint rather than a large language implementation. Arco is also intended to run on microcomputers and single-board computers. Arco can run as a standalone server or it can be linked into an application or loaded as a language extension. DSP code is linked according to a manifest, so your application is not burdened with 100's of unit generator implementations you have no plans to use.
- O2. In all configurations, Arco is based on O2, which provides message-based communications between the application or control language and the synthesis engine. O2 supports lock-free communication, real-time memory allocation, clock synchronization and other useful features. Built-in discovery lets you connect to an Arco server without messing with IP addresses or port numbers.
- Polymorphic Unit Generators. Arco unit generators (dsp objects) are polymorphic to simplify their use, accepting different types of input that can change on the fly. For efficiency, there are 2 sample rates: audio rate, computed in blocks of 32 samples, and block rate at 1/32 of audio rate. A signal can also be a scalar value that changes when updated by a message. Any signal can have multiple channels. Code to handle mixed types of inputs is generated automatically and the implementation is very efficient. (A few things are prohibited: block-rate unit generators do not accept audio-rate inputs, and while any input can be single-channel, all multi-channel inputs must have the same number of channels.
- Language Independence. Arco is agnostice about control, which can be located in an application or in another process, and control software can be written in any language. Pointers are avoided by "naming" unit generators with integers. Reference counting is used, although it can be largely hidden by libraries used on the control side, e.g. Serpent (programming language) garbage collects references to Arco, so users do not see reference counts.
- FAUST. Unit generators can be written in FAUST, allowing FAUST programs to be used in a dynamic environment with real-time patching and control. Users can focus on using a library of ready-made unit generators, but Arco is not limited to a fixed DSP library since new algorithms can be written in FAUST and added with an automated build system.
