Accelerating multi-channel filtering of audio signal on ARM processors

Tablets and smart phones are nowadays equipped with low-power processor architectures such as the ARMv7 and the ARMv8 series. These processors integrate powerful SIMD units to exploit the intrinsic data-parallelism of most media and signal processing applications. In audio signal processing, there exist multiple problems that require filtering operations such as equalizations or signal synthesizers, among others. Most of these applications can be efficiently executed today on mobile devices by leveraging the processor SIMD unit. In this paper, we target the implementation of multi-channel filtering of audio signals on ARM architectures. To this end, we consider two common audio filter structures: FIR and IIR. The latter is analyzed in two different forms: direct form I and parallel form. Our results show that the SIMD-accelerated implementation increases the processing speed by a factor of 4 with respect to the original code, and our hand-tuned SIMD implementation outperforms the auto-vectorized code by a factor of 2. These results allow us to deal in real time with multi-channel systems composed of 260 FIR filters with 256 coefficients, or 125 IIR filters with 256 coefficients, of INT16 data type.