Time-variant filtering

# Here, we define two filters applied at the beginning of the
# record, then one filter in the middle, and two more applied
# at the end.
# Transitions between the time intervals of the filters are performed using
# Hanning (cosine) tapers described by lists RAMP.


*call	filter
polygon	general			# filter 1
2	0	4	1	20	1	40	0

bworth	lp			# filter 2
2.0	4.0

ramp	1000	4000	# from 1000 to 4000 ms, gradually change to the second
			# group of filters

polygon	general			# filter 3
3	0	6	1	20	1	40	0

bworth	lp			# filter 4
4.0	8.0

bworth	hp			# filter 5
20.0	30.0

ramp	10000	15000	# from 10000 to 15000 ms, gradually change to the third
			# group of filters

bworth	lp			# filter 6
2.0	4.0

bworth	hp			# filter 7
10.0	20.0

# and so on, as many filters as you like...