[Discuss-gnuradio] iir filter - alpha ?

[cswiger]

Could somebody clue me in: gr_simple_squelch_cc takes a 'threshold'
and an 'alpha' factor for the iir filter. The magnitude squared of
the signal is formed and run thru the iir filter and compared to
the threshold.

What is the significance of alpha, i.e., it's relation to the
frequency of the signal and amount of 'smoothing' done? Basically
I need to set the right alpha for best smoothing for a range
of frequencies.  Been doing it trial&error but need an automatic
method now - I use it to measure signal strength.

TIA

--Chuck