Posted on:

Hi everybody, since my last post (see below) I have tried to assemble some code (Matlab). Is that correct? (I'm a total novice to filtering, so I'm unsure about pretty much everything) here's my "code" which ought to comply to the specifications mentioned further below: first Fourier transform my voxel timeseries (vector 1) then construct a second vector (vector 2) as described by iorder = 2; f_half = 0.08; r = (vector1 ./ f_half) .^ (2*iorder); factor = 1./(1 + r); eventually, I would multiply the corresponding elements of vector 1 and vector 2 and then apply inverse Fourier Transformation to the resulting vector, which then should be my filtered data. The whole code should look something like this vector1 = FourierTransform(voxel_time_series); % lowpass filter iorder = 2; f_half = 0.08; r = (vector1 ./ f_half) .^ (2*iorder); vector2 = 1./(1 + r); data_filtered = inverseFourierTransform(vector1 .* vector2); Does this make sense at all? I'm particularly unsure if f_half is in Hertz as I need it to be... Thanks in advance! Last post: Hello! I have been struggeling to create a bandpassfilter for = which I=20 have been given certain specification. Probably quite easy for some of=20 you. Here's the problem: I have a series of 304 = measurements (one=20 value every 2 seconds) which I would like to (probably) bandpassfilter = so that=20 only frequencies between 0.009 and 0.08 Hz are left afterwards. The = problem is=20 that I have specifications from an article which I do not understand. It = simply=20 says: "The data were bandpass filtered in the complex = Fourier domain=20 using multiplication by frequencydependent factors computed using the = following=20 FORTRAN code: highpass factor: r =3D (f/f_half)**2*iorder factor =3D r/(1 + r) lowpass factor: r =3D (f/f_half)**2*iorder factor =3D 1/(1 + r) (In FORTRAN, the ** operator indicates = exponentiation.) For the=20 highpass component, f_half was 0.009 Hz and iorder was 1. For the = lowpass=20 component, f_half was 0.08 Hz and iorder was 2. Gentle slopes about the=20 halffrequency were chosen specifically to avoid ringing." Can anyone give me some praktical help on = this? Thanks in advance! Tim
Posted on:

sorry, I have no answer to your question, but do you know this tutorial page: http://www.neurotraces.com/scilab/scilab2/index.html "An introduction to the treatment of neurophysiological signals using Scilab"