I had some ideas for some audio effects and dusted off an old Analog Devices ADSP-SC589 dev board that’s been sitting idle in a drawer for the last few years. The ADSP-SC589 is a real-time processor with 2 SHARC+ DSP cores and an ARM Cortex-A5 processor. I’ve played with rust a bit, and wanted to try it out for something embedded, and this seemed like a great opportunity. Theres no LLVM backend for the SHARC architecture, so I’m stuck with C/C++ and Analog’s compiler there, but I figured I would write the code that runs on the ARM core and orchestrates the DSPs and peripherals in rust.

In Part I and Part II of this series we developed a finite impulse response audio filter taking advantage of some of the DSP functions in the Accelerate Framework. The improvements we made in Part II were fairly straightforward, mostly replacing naive hand-coded loops with optimized implementations, taking advantage of specialized processor instructions to speed up our filter. In this installment, I’ll show you a less obvious improvement which can result in huge speedups for higher-order filters.

In Part I of this 3-part series we created a simple FIR filter. In this part we will look at some ways of improving the implementation using some functions from the Accelerate Framework. The Accelerate Framework The accelerate framework provides a C API with functions for linear algebra, matrix math, DSP, and image processing. In this case we will specifically be focusing on the vDSP functions. The functions provide vectorized implementations of common functions using specialized instruction sets (SSE, NEON, etc) or DSP hardware on your processor.