CODEWITHSUNDEEP
c++filteringsignal-processing
r.a.m-
r.a.m-

Reputation: 594

C++ FIR noise filter

I'm digging up some info about filtering the noise out of my IQ data samples in C++.

I have learned that this can be done by using a simple filter which calculates the average of last few data samples and applies it to the current sample.

Do you have any further experience with this kind of filtering or do you recommend using some existing FIR filtering library?

Thanks for your comments!

Upvotes: 0

Views: 2941

Answers (1)

No-Bugs Hare
No-Bugs Hare

Reputation: 1638

Unfortunately, it is not as simple as "just get some library and it will do all the work for you"; digital filters is a quite complicated subject.

  1. It is easy to apply digital filter to your data only if your measurements come at fixed time intervals (known as "sample rate" in digital filters). Otherwise (if time intervals vary), it is not trivial to apply digital filters (and I suspect you might need FFT to do it, but I might be wrong here).

  2. Digital filters (both IIR and FIR) are interesting in that as soon as you know coefficients, you don't really need a library, it is easy to write it yourself (see, for example, first picture here: https://en.wikipedia.org/wiki/Finite_impulse_response : looks simple, right?); it is finding coefficients which is tricky.

  3. As a prerequisite to find out coefficients, you need to understand quite a lot about filters: you need to know what kind of filter you need (if it is after demodulation - you'll likely need low-pass, otherwise see comment by MSalters below), you need to understand what "corner frequency" is, and you need to realize how to map those frequencies to your samples (for example, you can say that your samples are coming once per second - or at any other rate, but this choice will affect your desired "corner frequency"). As soon as you've got this understanding of "what you need in terms of digital filters" - finding coefficients is quite easy, you can do it either in MatLab, or using online calculator, look for "digital filter calculator" in Google.

Upvotes: 1

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