# Analog equivalent for transition width in Digital radios

I have started off with GNUradio and I am not sure if I understand the transition width parameter available in GNU radio companion filter blocks .

As per online documentation transition width of a digital filter is the frequency difference between the cutoff frequency of the passband and the start frequency of the stop band.

What does the stop band mean? Does it have an analogue for Analog filters?

I suspect that the stop band is a concept specific to digital filters and does not have an Analog equivalent. If this is the case, then what is the origin for this difference between Analog and digital filters?

• the terms “stop band”, “pass band” are common to digital and analog filters and have a great deal of equivalence. Voltages come out of analog filters while numbers that often correspond to voltages come out of digital filters. your suspension is erroneous. The term “boy band” is unrelated to either analog or digital filters, just in case that your suspect so. – Stanley Pawlukiewicz Aug 3 '18 at 16:18
• @StanleyPawlukiewicz not sure what you mean by Boy Band and google is not helping. Could you describe what Stop band would mean for an Analog Low pass filter? If I am correct, an analog filter is described completely by its passband gain and its cutoff/3dB frequency – ijuneja Aug 3 '18 at 18:36
• I see your point but a high pass filter has a low pass stop band. Even an analog low pass filter has will have a stop band rejection specification. – Stanley Pawlukiewicz Aug 3 '18 at 18:57
• Boy band en.m.wikipedia.org/wiki/Boy_band – Stanley Pawlukiewicz Aug 3 '18 at 19:02
• See en.m.wikipedia.org/wiki/Elliptic_filter for the explicit use of the term stop band with an analog filter – Stanley Pawlukiewicz Aug 3 '18 at 19:10

for an analog filter where there is a stop band specification.

There are digital filters that are based on analog prototypes including the butterworth, elliptic, and caur types.

One can typically match an IIR digital filter with an analog filter.

Linear phase FIR filters are the big difference between analog and digital filters.

The strongest argument for equivalence is that with appropriate A/D and D/A converters, one can in theory substitute an analog for a digital filter or vice versa in a system.