Thanks very much for the link & apologise for being a bit slow. I am still struggling a bit with translating the articles I'm reading on band pass filters into trading terms.

In the examples I am reading a band pass filter normally takes two frequencies and basically any frequencies that are outside that range are removed. So with the band pass filter above are we saying that the centre frequency is 30 bars (so not looking at the shorter time bars as we want to filter out the noise & also not looking at the longer time bars so that the long term trend is removed) and the width of 2 means that the band pass will reject any bars outside the range of 28 to 32. Is that correct or completely wrong?

Thanks once more!