I'm new to signal processing and would like some insights about the best way to filter simple data without being too computationally intensive.
I have an audio signal and I want to extract a single frequency (21khz) from it.
This frequency represents whether something is on or off.
I figured a simple amplitude threshold would do the trick to guess the on or off state but I can't think of a good way to single it out so I can threshold it.
I thought about doing it in the frequency domain but using the FFT seems a bit overkill.
I'm sorry if this is obvious but I'm not familiar with signal processing.