I dont exactly understand what is going on with my convolution. I am trying to convolve my data with a {+1, -1} wavelet, downsample by 2, and convolve again. The problem I am having is that if N values of data go in, it comes out with N+1 values. When I set up the VI to process a large data file using a loop, the issue becomes much much larger. How do I solve the issue with my convolution? What do I have to do after convolving to eliminate the excess?

As I said, a convolution with 1,-1 is just a simple derivative. I don't know why you would jump through all these flaming hoops of advanced signal processing, if all you need is a pairwise difference. Is somebody testing you? 😮 The attached modification shows what I mean. As you can see, the results are identical!

LabVIEW

Need some help with Convolution

Solved!

Author

I've found the problem,

the 1D convolution operation leaves a number of unncesseary (and extra) entries in the beginning of the post convolution array as a result of the algorithm used. the number of extra terms is equal to the size of the kernel (in this case 1,-1) divided by 2. If I had convolved with a 4 term wavelet, I would have to remove 2. The best way to do it is to use the split array, and split with the size of wavelet/2. the second subarray is equal in size to the original and has no initialization issues.