This is definitely a fun trick in the DSP world. Be aware, however, that you will not get the same rolloff as a highpass filter with matching coefficients for most filters (except for onepole~ or a biquad~ using only poles), so if you want a highpass with a steep rolloff, use a cascade of biquad~'s. If memory serves, the subtraction works on the poles of the filter, which is why in the attached demo this works with a cascade of onepole~s, but not with a cascade of biquad~s.
yeah i looked, but i guess i can only make IIR filters from filter design tool. I found this the following patch from a msp tutorial where i can put my filter co-efficient and see the response but i cant actually use it to filter my audio signal.
thanks for the quick replies. I am looking into the example patch of buffir~ since yeastarday. i cant seem it to figure out how it is actually working. I understood i will need a buffer to save my impulse response in order to use the buffir~ object. but i cant go any further. it would be great if you give it a try. i am stuck in the office with this one.