# Discrete Fourier Transform Frequency

Hi everybody,

I'm in the process of writing a discrete Fourier transform program using the algorithm on the DFT wikipedia page. When I throw in functions that I know the frequency domain signal of it gives the predicted shape but I have absolutely know idea how to generate a frequency axis.

Does anybody here know how I can compute the frequency values?

Thanks in advance.

Chris

## Answers and Replies

Redbelly98
Staff Emeritus
Science Advisor
Homework Helper
Try using a sine function at a specific frequency. Then whatever you get for the Fourier Transform corresponds to that frequency.

jbunniii
Science Advisor
Homework Helper
Gold Member
Hi everybody,

I'm in the process of writing a discrete Fourier transform program using the algorithm on the DFT wikipedia page. When I throw in functions that I know the frequency domain signal of it gives the predicted shape but I have absolutely know idea how to generate a frequency axis.

Does anybody here know how I can compute the frequency values?

Thanks in advance.

Chris

The DFT gives you N evenly spaced samples of the DTFT (discrete-time Fourier transform). The frequencies corresponding to these samples are

$$\frac{n}{N} F_s$$

where $n = 0,1,\ldots,N-1$ are the indices of the samples, and $F_s$ is the sampling frequency of the input sequence.