# Finite Impulse Response Filter (FIR Filter)

This operator implements a finite impulse response filter.

It returns a weighted average of the current and previous pings.

Echoview accepts a single operand of the following data types as input:

• Linear
• Multibeam magnitude
• Multibeam Sv
• Multibeam TS
• Multibeam unspecified dB
• Power dB
• Sv
• TS
• Unspecified dB

See: FIR algorithm.

## Settings

The Finite Impulse Response Filter Variable Properties dialog box pages include (common) Variable Properties pages and these operator pages:

### FIR Filter page

 Setting Description Coefficient Enter the coefficient to be used to alter signal content.

## Algorithm

### FIR filter

The result for any given data point may be written as:

Result(0,d) = Operand(0,d)
Result
(p,d) = C * Operand(p,d) + (1-C) * Operand(p-1,d)            where p>0

Where:

p identifies the ping
d
identifies the data point (each ping contains a number of data points)
C
is the coefficient entered on the FIR page of the Variable Properties dialog box.
Result
(p,d) is the value of the data point d in ping p in the resulting variable.
Operand
(p,d) is the value of the data point d in ping p in the operand variable.

Hence, if C = 1 the filter will make a copy of the operand variable, and if C = 0, the filter will make a copy of the operand variable shifted forward in time by one ping.

Notes:

• This operation involves two pings, both from the operand variable. These pings must have matching ping geometry. If they do not there will be no resulting ping. See Using multiple operands for further information.
• FIR calculations are carried out in the linear domain. dB values are converted to linear for calculations and the output is re-expressed in dB.