Implementing digital audio effects using a hardware/software co-design approach

Digital realtime audio effects as of today are realized in software in almost all cases. The hardware platforms used for this purpose reach from multi purpose processors like the Intel Pentium class over embedded processors (e.g. the ARM family) to specialized DSP. The upcoming technology of complete systems on a single programmable chip contrasts such a software centric solution, because it combines software and hardware via some co-design methodology and makes for a promising alternative for the future of realtime audio. Such systems are able to combine the vast amount of computing power provided by dedicated hardware with the flexibility offered by software in a way the designer is free to influence. While the main realization vehicles for these systems - FPGAs - were already promising but unfortunately offered limited possibilities a decade ago [1] they have made rapid progress over the years being one of the product classes that drive the silicon technology of tomorrow. We describe an example for such a realtime digital effects system which was developed using a hardware/software co-design method. While digital realtime audio processing takes place in low latency dedicated hardware units the control and routing of audio streams is done by software running on a 32 bit NIOS II softcore processor. Implementation of the hardware units is done using a DSP centric methodology for raising the abstraction level of VHDL descriptions while still making use of standard of the shelf FPGA synthesis tools. The physical implementation of the complete system uses a rapid prototyping board tailored for communications and audio applications based on an Altera Cyclone II FPGA.