Hi guyz, just a new problem, I connected microphones to my 1701 and decided to filter all the sound lower than 22khz. That is how I checked: from an external generator I generated a signal 19.56khz, connected microphones to the input, then connected high pass second order butterworth filter with corner freq 22khz, then multiplied filtered signal on 20khz sine wave and listened to the output. If there was a signal coming through, it would be modulated and would come through the output as 440hz tone, if filter works then there will be no sound.
The problem is, the filter seems to filter almost nothing! When I switch it on, the 440hz tone becomes just a little tiny bit quieter. Then I tried a crossover, also with the same result. What is wrong guyz? Do filters work fine? Do I do something wrong? How to filter unwanted signal thoroughly?