MATLAB signal processing toolbox (sptool)

[Romulus3]

Hey guys, I am using the sptool GUI to design and apply filters to noisy ECG signals. I understand the concepts behind lowpass, highpass, and bandpass filters. But I'm confused with the parameters of FDA tool.

Here are my questions:
1) In the FDA tool, there is a bandstop filter. what is bandstop?
2) What do the parameters Fstop and Fpass mean? Do they define frequency intervals for the filters?
3) If my guess about 2) is right, why would you need an interval of frequencies of, let's say, lowpass? Aren't frequency intervals only applicable to bandpass filters?

I'm very confused.

Thanks.

 

[abdo375]

1) A band-stop filter is a filter that stops certain bands of frequencies and passes the rest.

2) The fdatool doesn't assume that you're working with an ideal filter, in an ideal filter; take a low pass filter for example, there is a single frequency that blew it the signal will pass and above it the signal will be zero, unfortunately this filter is not realizable because there can not be this kind of sharp transition in real life, so what happens in practical filters is that there is a period in which the filter goes from having a gain equal to or larger than 1 to having a near zero gain, this period starts at Fpass and ends at Fstop.