Choosing dimension for filter

I have voltage recordings from x sensors for y time-frames, each spanning z seconds. This is stored in a x*y*z matrix. Now, I designed an iirnotch to remove the line noise (60 Hz). When I apply the filter to the matrix using filtfilt, am I correct in assuming that the filter will run along the x dimension, and is this choice of dimension appropriate?

Answer 1

[Star Strider]

I believe so.

From the filtfilt documentation for x:

‘The function operates along the first array dimension of x unless x is a row vector. If x is a row vector, then the function operates along the second dimension.’

So I believe it will operate along each column (down the rows) of the matrix and across all dimensions. (I have only filtered 2D matrices with it, not 3D.)

.

[Aboltabol]

My matrix has sensors as rows, events as columns, and time as pages. Now, ought not the filter run per sensor per event along the time dimension i.e. the third dimension (page)?

[Star Strider]

Yes, it should, however that information did not originally appear.

Use the permute function to put them in the order you want them, for example —

A = randn(12, 5, 30);               % Sensor x Event x Time
Ap = permute(A, [3 1 2]);
PermutedSize = size(Ap)             % Time x Sensor x Event

PermutedSize = 1×3

30 12 5

That appears to me to be appropriate for the filtering you want to do. If it is not, changing it is straightforward.

.