FILTERBANK

Multi-band reson instrument.

in RTcmix/insts/jg

quick syntax:

FILTERBANK(outsk, insk, dur, AMP, ringdowndur, inputchan, PAN, CFREQ1, BANDWIDTH1, RELAMP1, … CFREQN, BANDWITHN, RELAMPN)

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 input duration seconds no no  
p3 amplitude multiplier relative multiplier of input signal yes no  
p4 ring-down duration seconds no no  
p5 input channel - no no  
p6 pan 0-1 stereo; 0.5 is middle yes no  
p7 center freq for filter Hz or oct.pc* yes no see note below
p8 bandwidth for filter multiplier of the center frequency, 0-1 yes no  
p9 relative amplitude for filter in final construction - yes no  
…          

The remaining pfields are triples following the format of p7-p9. Up to 60 cf-bw-amp triples can be specified.

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

* If the value of the center frequency pfield(s) (“CFREQ1 … CFREQN”) is < 15.0, it assumes oct.pc. Use the pchcps scorefile convertor for direct frequency specification below 15.0 Hz.

Author: John Gibson, 25 Feb 2007

FILTERBANK is very similar to the older IIR instrument. It builds a series of infinite impulse response (or recursive) filters with center frequency, bandwidth, and amplitude boost defined in triplets. These filters, combined together, allow the specification of complex frequency-response curves.

Usage Notes

The two main differences between FILTERBANK and IIR are, first, the elimination of the setup subcommand for designing the filter in favor of extended pfield-parameters in the main FILTERBANK note specification. This leads to the second main difference: each of the center-frequency/bandwith/relative-amplitude may be dynamically modified using the pfield-enabled control system. This gives the FILTERBANK instrument a high degree of flexibility.

oct.pc format generally will not work as you expect for the center frequency specifications if the pfield changes dynamically. This is because of the ‘mod 12’ aspect of the pitch-class (.pc) specification. Use direct frequency (hz) or linear octaves instead.

The bandwith of each filter is specified as a multiplier of the center frequency of each filter. The older IIR instrument had an option to specify this bandwidth directly as a Hz value. This is not the case with FILTERBANK.

The point of the ring-down duration parameter (p4) is to let you control how long the filter will sound after the input has stopped. Too short a time, and the sound may be cut off prematurely, resulting in a click.

The output of FILTERBANK can be either mono or stereo.

Sample Scores

very basic:

   rtsetparams(44100, 2)
   load("FILTERBANK")
   
   rtinput("mysound.aif")
   inchan = 0
   inskip = 0
   dur = DUR()
   ringdur = 10
   
   amp = 0.25
   bw = 0.0003
   
   cf1 = maketable("line", "nonorm", 100, 0,200, 1,1200)
   cf2 = maketable("line", "nonorm", 100, 0,1100, 1,300)
   cf3 = maketable("line", "nonorm", 100, 0,600, 1,2200)
   cf4 = maketable("line", "nonorm", 100, 0,2000, 1,900)
   
   start = 0
   FILTERBANK(start, inskip, dur, amp, ringdur, inchan, pan=0.5,
      cf1, bw, g=1, cf2, bw, g=1, cf3, bw, g=1, cf4, bw, g=1)

slightly more advanced:

   rtsetparams(44100, 2)
   load("FILTERBANK")
   
   rtinput("mysound.aif")
   inchan = 0
   inskip = 0
   dur = DUR()
   ringdur = 5
   
   amp = 0.1
   bw = maketable("line", "nonorm", 1000, 0,0.01, dur,0.001, dur+ringdur,0.001)
   
   start = 0
   FILTERBANK(start, inskip, dur, amp, ringdur, inchan, pan=0.1,
      cf=9.02, bw, g=1,
      cf=9.09, bw, g=1,
      cf=10.01, bw, g=1,
      cf=10.06, bw, g=1,
      cf=11.02, bw, g=1)
   FILTERBANK(start, inskip, dur, amp, ringdur, inchan, pan=0.9,
      cf=8.02, bw, g=1,
      cf=9.05, bw, g=1,
      cf=10.03, bw, g=1,
      cf=10.10, bw, g=1,
      cf=11.04, bw, g=1)

See Also

maketable, BUTTER, ELL, EQ, FIR, FILTSWEEP, FOLLOWBUTTER, IIR, JFIR, MOOGVCF, MULTEQ SPECTEQ, SPECTEQ2