Gr_firdes cutoff frequency

I’m looking benchmark program and now found use of gr.firdes.low_pass:

    chan_coeffs = gr.firdes.low_pass (1.0,                  # gain
                                      sw_decim *

self.samples_per_symbol(), # sampling rate
1.0, # cutoff
frequency: midpoint of trans. band
0.5, # width
trans. band
gr.firdes.WIN_HANN) # filter

I checked that low pass function in doxygen, and it says cutoff
has unit measure [Hz].
Recalling above expression, it says that cutoff frequency is 1.0 Hz
Is it right? Or is it a factor that is normalized to the sampling

I’m asking about it because I want to use band_pass filter and I have no
idea what value I have to choose for low/high cutoff frequency

Hi Songsong,

the cutoff frequency is relative to the given sampling rate, whatever
that is. The firdes stuff doesn’t know about the “true” sampling rate.
It’s not uncommon to set the sampling rate to 1 and then have cutoff
somewhere in between 0 and 1.


On Mon, Dec 12, 2011 at 02:53:07PM +0900, Songsong G. wrote:

Communication & Networks Lab

IT Convergence Engineering (ITCE), POSTECH, Korea

+82 10 8338 1229, gee.songsong at gmail . com

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