Bandpower function produces same results for different bands

I'm using the bandpower function with different frequency bands. However, the results from each band are the same. The code I'm using is:

avpow = bandpower(x, fs, [0.0 0.4]) 
HF = bandpower(x, fs, [0.15 0.4]) %high frequency
LF = bandpower(x, fs, [0.04 0.15]) %low frequency
VLF = bandpower(x, fs, [0.0033 0.04]) %very low frequency

Any help is greatly appreciated.

Answer 1

[Greg Dionne]

You might not be giving it enough data to resolve the lower frequencies. You generally will have a resolution on the order of fres = fs / length(x). Since your lowest frequency band ends at 0.04 Hz, make sure fres << 0.04 Hz.

[chels19]

Thanks. The frequency it was originally recorded at was 512. Should I be using 512 in my code as fs?

fres = 512 / length(x) returns 2.473

Or should I used the maximum frequency I'm looking for (0.4)?

fres = 0.4 / length(x) returns 0.00193