# FFt scale

Discussion in 'Programmer's Corner' started by froztbear, Apr 12, 2010.

1. ### froztbear Thread Starter New Member

Apr 12, 2010
1
0
Hi all.
I am new in this forum and looking for some help.
I have a sampled signal y. (y=chirp signal) In the task you are supposed to sample 8000 values. Then divide it in a different amount of blocks with N values in each block. Like N = 128. I divide it into 62 blocks with 128 values in each block. Block 1 = y(1:128) etc.

When I want to plot the abs of FFT i use the scaling: block_abs,j)=(2/N(n))*abs(fft(block_y,j)))

The 2/N(n) in this case is 2/128.. N = [32 64 128 256 etc]

When I run the program and plot the amplitude vs. freq, the amplitude is 1 for N = 32 64 128 but for 256 512 etc. The amplitude divides by 2 all for each step. (correct=1??)

The objection is to analyze y=chirp.... And the frequencys are in correct itnerwall for all N. But not the amplitud. The amplitude should be the same undepending on the number of blocks and numbre of N to compute the FFT? And it should be =1 ?

Hope you can help!