# Detect a specific frequency in an input signal without using fourier transform

I am trying to learn FPGA programming, and I would like to analyze an audio input.
I would like to know what kind of frequencies are present in the signal but without using Fourier transform - there are two reasons for this.

First one is I dont need to know the exact frequency of the incoming signal, and the second reason is simple - I have just started learning FPGA and Fourier transform is beyond my skill level to implement.

So, are there any methods of checking if a signal of given frequency is part of the audio input? Say, I would like to know if any signal in frequency range 3KHz-5KHz is present in the input. How can such a problem be approached?

Edit. My first thought was to use a pair of low and high pass filters to do the job, but I am not sure if this would work well, because they only pass through the current signal.

• This sounds like Electrical Engineering. Mar 16, 2021 at 22:58
• @YuvalFilmus I wasn't really sure. I am studying CS and perceive this mostly as an "algorithmic" problem, but I will remove this question and move it to Electrical if no answers appear, thank you for Your suggestion. Mar 16, 2021 at 23:17
• This is signal processing, which is what electrical engineers do. Mar 16, 2021 at 23:18
• You could use a band filter. In fact, you don’t really need to filter your signal, just to compute some inner product. Mar 16, 2021 at 23:19