So far we have worked with different transformations between the analog space S and into the duty to domain Z. And so we have done this with two transformations so far. This was so called impulse invariance. And the other one was the matched Z transform. So the main problem with these transforms is a following. So if we look at a analog response here, so this is our analog domain. So if we have an analog response here, so we have a h of j and then capital omega for analog frequencies. And we've got here's omega. And so for example we have a low pass response. So that's a low pass. So the frequency axis here, this goes to infinity. So we have no limitations. So we're starting from zero and this goes to infinity here. The problem now is that our digital filter won't do that. So our digital filter stops at some point here. So let's see this is here for digital filter as a Nyquist frequency. So we know that above the Nyquist frequency this spectrum just repeats. So this means that for the Nyquist frequency this would go up. So the response, this is the response here of our analog filter. And this one here, this is the response of the digital filter. So this means the bottom line is at we're getting a very poor filter response. So if we're limiting, if we define this frequency here in our digital filter, filter pi, then essentially this is only the usable region of our digital filter here.