(1) Analog-to-digital conversion (A/D conversion): Converting analog signals into digital signals is a process of discretizing independent variables and amplitudes at the same time, and the basic theoretical guarantee is sampling theorem.
(2) Digital signal processing (DSP): including transform domain analysis (such as frequency domain transformation), digital filtering, identification and synthesis.
(3) Digital-to-analog conversion (D/A conversion): The processed digital signal is restored to an analog signal. Usually, this step is unnecessary.
These methods or devices for signal processing already exist, so you can't apply for a patent for pure signal processing method, because its technical points already exist, which doesn't conform to the novelty and creativity of invention and creation, so you can't get a patent.
I hope it helps you ~