Filter grammar¶
SeisComP3 supports stringbased filter definitions. This section covers available filters and their parameters.
The filter definition supports building filter chains (operator >> or >) as well as combining them with basic mathematical operators like +, , *, /, ^ (exponentiation) and .  (absolute value).
Example¶
A(1,2)>>(B(3,4)*2+C(5,6,7))>>D(8)
where A, B, C and D are different filters configured with different parameters. If a sample is filtered it passes the following stages:
s = a sample
 filter s with A: sa = A(1,2)(s)
 filter sa with B: sb = B(3,4)(sa)
 sb = sb * 2
 filter sa with C: sc = C(5,6,7)(sa)
 add sb and sc: sbc = sb + sc
 filter sbc with D: sf = D(8)(sbc)
sf = final sample
The default filter applied by scautopick is
RMHP(10)
>> ITAPER(30)
>> BW(4,0.7,2)
>> STALTA(2,80)
It first removes the offset. Then an ITAPER of 30 seconds is applied before the data is filtered with a fourth order Butterworth bandpass with corner frequencies of 0.7 Hz and 2 Hz. Finally an STA/LTA filter with a shorttime time window of 2 seconds and a longterm time window of 80 seconds is applied.
Filters¶
The following filter functions are available. If a filter function has no
parameters it can be given either with parentheses (e.g. DIFF()
) or without (e.g. DIFF
).

AVG
(timespan)¶ Calculates the average of preceding samples.
Parameters: timespan – Time span in seconds

BW_LP
(order, hifreq)¶ Butterworth lowpass filter realized as a causal recursive IIR (infinite impulse response) filter.
Parameters:  order – The filter order
 hifreq – The corner frequency

BW_HP
(order, lofreq)¶ Butterworth highpass filter realized as a causal recursive IIR (infinite impulse response) filter.
Parameters:  order – The filter order
 lofreq – The corner frequency

BW_HLP
(order, lofreq, hifreq)¶ Butterworth highlowpass filter realized as a combination of
BW_HP()
andBW_LP()
.Parameters:  order – The filter order
 lofreq – The lower corner frequency
 hifreq – The upper corner frequency

BW
(order, lofreq, hifreq)¶ Alias for
highlowpass filter
.

BW_BP
(order, lofreq, hifreq)¶ Butterworth bandpass filter (BW) realized as a causal recursive IIR (infinite impulse response) filter. An arbitrary bandpass filter can be created for given order and corner frequencies.
Parameters:  order – The filter order
 lofreq – The lower corner frequency
 hifreq – The upper corner frequency

DIFF
()¶ Differentiation filter realized as a recursive IIR (infinite impulse response) differentiation filter.
The differentiation loop calculates for each input sample s the output sample s’:
s' = (sv1) / dt v1 = s;

INT
([a = 0])¶ Integration filter realized as a recursive IIR (infinite impulse response) integration filter. The weights are calculated according to parameter a in the following way:
a0 = ((3a)/6) * dt a1 = (2*(3+a)/6) * dt a2 = ((3a)/6) * dt b0 = 1 b1 = 0 b2 = 1
The integration loop calculates for each input sample s the integrated output sample s’:
v0 = b0*s  b1*v1  b2*v2 s' = a0*v0 + a1*v1 + a2*v2 v2 = v1 v1 = v0
Parameters: a – Coefficient a.

ITAPER
(timespan)¶ A onesided cosine taper.
Parameters: timespan – The timespan in seconds.

RMHP
(timespan)¶ A highpass filter realized as running mean highpass filter. For a given time window in seconds the running mean is subtracted from the single amplitude values. This is equivalent to highpass filtering the data.
Running mean highpass of e.g. 10 seconds calculates the difference to the running mean of 10 seconds.
Parameters: timespan – The timespan in seconds

RM
(timespan)¶ A running mean filter. For a given time window in seconds the running mean is computed from the single amplitude values and set as output. This computation is equal to
RHMP
with the exception that the mean is not subtracted from single amplitudes but replaces them.RMHP = selfRM
Parameters: timespan – The timespan in seconds

SM5
([type = 1])¶ A simulation of a 5second seismometer.
Parameters: type – The data type: either 0 (displacement), 1 (velocity) or 2 (acceleration)

STALTA
(sta, lta)¶ A STA/LTA filter is the ratio of a shorttime average to a longtime average calculated continuously in two consecutive time windows. This method is the basis for many trigger algorithm. The shorttime window is for detection of transient signal onsets whereas the longtime window provides information about the actual seismic noise at the station.
Parameters:  sta – Shortterm time window
 lta – Longterm time window

WA
([type = 1[, gain=2800[, T0=0.8[, h=0.8]]]])¶ The simulation filter of a WoodAnderson seismometer. The data format of the waveforms has to be given for applying the simulation filter (displacement = 0, velocity = 1, acceleration = 2), e.g. WA(1) is the simulation on velocity data.
Parameters:  type – The data type: 0 (displacement), 1 (velocity) or 2 (acceleration)
 gain – The gain of the WoodAnderson response
 T0 – The eigenperiod in seconds
 h – The damping constant

WWSSN_LP
([type = 1])¶ The instrument simulation filter of a WorldWide Standard Seismograph Network (WWSSN) longperiod seismometer.
Parameters: type – The data type: 0 (displacement), 1 (velocity) or 2 (acceleration)

WWSSN_SP
([type = 1])¶ Analog to the WWSSN_LP, the simulation filter of the shortperiod seismometer of the WWSSN.
Parameters: type – The data type: 0 (displacement), 1 (velocity) or 2 (acceleration)