Brett (and anyone else who might have some insight.)

Several months ago, you and I had discussed a comb filter implementation. At the time, I was asking why the simulation/probe was not working properly. We assumed that this was just a simulation problem and moved on. Now we are finding that the filter does not actually work on the hardware as expected.

The equation that we want is : y(n) = x(n) - x(n - N) + alpha*y(n-N).

I have attached my implementation, and I'm not seeing what is wrong. It behaves as if the y(n-N) is not there.

Best regards,

Bob

Hi Bob,

I tested the filter with the feedback taken from the sum total, and its delay set to N-1 = 399 (as it turns out, this did make a difference). To gauge its frequency response I set up a swept VCO, reading the filter output from a peak detector and Real-Time Display. Here's the results with alpha = 0.5:

and at alpha = 0.9:

So adjusting the alpha is affecting the result as expected. This is about all I can do, perhaps we need to redirect your question to an ADI engineer (such as Brett) to handle any remaining differences between your measured result and the Matlab theory. It was fun to play with though. I always wondered how to make a comb filter. Thanks for sharing this with me!

Bob B.