FIR

Simple finite impulse response filter.

in RTcmix/insts/std

quick syntax:

FIR(outsk, insk, dur, AMP, ncoefficients, coefficients…)

CAPITALIZED parameters are pfield-enabled for table or dynamic control (see the maketable or makeconnection scorefile commands). Parameters after the [bracket] are optional and default to 0 unless otherwise noted.

Param Field Parameter Units Dynamic Optional Notes
p0 output start time seconds no no  
p1 input start time seconds no no  
p2 duration seconds no no  
p3 amplitude multiplier relative multiplier of input signal yes no  
p4 total number of filter-equation coefficients - no no  
p5 … the coefficients (up to 99 fir coefficients) - no no  

Parameters labled as Dynamic can receive dynamic updates from a table or real-time control source.

NOTE: mono input / mono output only

FIR creates a finite impulse response filter using the filter coefficients passed to the instrument. The filter is non-recursive (i.e. only past inputs are used in the equation), in the form:

Usage Notes

FIR can be used to design fairly complex filters, although the phase-shifting due to a long stream of past inputs is an inherent design problem with basic FIR filters. The trick is to find the right set of coefficients. There are a number of good web sites that will generate FIR coefficients given a frequency-graph type of specification.

Sample Scores

very basic:

   rtsetparams(44100, 1)
   load("FIR")

   rtinput("mysound.aif")
   FIR(0, 0, 7.0, 0.7, 7, 0.9, 0.1, 0.69, -0.49, 0.314, 0.2, 0.09)

See Also

BUTTER ELL EQ FILTERBANK, FILTSWEEP, IIR, JFIR, MOOGVCF, MULTEQ