The essential process to analyze signals from multicarrier communication systems is to isolate independent communication channels using a channelizer. To implement a channelizer in software-defined radio systems, the Polyphase Filterbank (PFB) is commonly used. For real-time applications, the PFB has to process the digitized signal faster or equal to its sampling rate. Depending on the underlying hardware, PFB can run on a CPU, a Graphical Processing Unit (GPU), or even a Field-Programmable Gate Arrays (FPGA). CPUs and GPUs are more reconfigurable and scalable platforms than FPGAs. In this paper, we optimize an existing implementation of a CPU-based channelizer and implement a novel GPU-based channelizer. Our proposed solutions deliver an overall improvement of 30 % for the CPU optimization on Intel Core i7-4790 @ 3.60 GHz, and a 3.2-fold improvement for the GPU implementation on AMD R9 290, when compared to the original CPU-based implementation.