MULTEQ

Multi-band equalizer.

in RTcmix/insts/std

quick syntax:

MULTEQ(outsk, insk, dur, AMP, MASTERBYPASS, EQTYPE1, FILTFREQ1, FILTQ1, FILTAMP1, FILTBYPASS1, … EQTYPEN, FILTFREQN, FILTQN, FILTAMPN, FILTBYPASSN)

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 master 0: bypass off, 1: bypass on yes no usually use 0
starting with p5, the next N pfields are quintuples describing each EQ band:
Param Field Parameter Units Dynamic Optional Notes
p5 EQ type “lowpass”, “highpass”, “lowshelf”, “highshelf”, “peaknotch” no no  
  numeric code for the filter type 1: lowpass, 2: highpass, 3: lowshelf, 4: highshelf, 5: peaknotch yes no dynamic when using numeric codes
p6 filter frequency Hz, 0 - Nyquist yes no  
p7 filter Q c. 0.5-10 yes no  
p8 filter gain (cut or boost dB yes no for shelf and peak/notch only
p9 bypass 0: bypass off, 1: bypass on yes no usually use 0
… pN-4, pN-3, pN-2, pN-1, pN

Not all have to specified; a maximum of 8 quintuples is allowed.

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

Author: John Gibson, 26 Sep 2004 Based on formulas by Robert Bristow-Johnson (“Audio-EQ-Cookbook”) and code by Tom St Denis (see musicdsp.org)

MULTEQ is a very flexible approach to signal filtering, especially when the pfield capabilities of each individual filter section is employed. The code is based on the EQ instrument.

Usage Notes

The individual bands of MULTEQ can be set to do several different types of filters (peak/notch, shelving and high/low pass types), depending on the setting of “EQTYPE” pfields for each one.

A standard ‘biquad’ DSP filter algorithm is used to build these different types of filters.

In addition to the filter frequency and gain, the ‘Q’ (“FILTQ”) can be used to determine how ‘steep’ each of the filter bands will be. Filter parameters for the individual bands are interpreted depening on what type of filter type is selected.

The “FILTAMP” parameter for each filter band is in dB, expressed as a boost (+dB) or a cut (-dB) that will deviated from the overall master ampilitude multiplier of the signal (“AMP”, p3).

MULTEQ is either mono-to-mono or stereo-to-stereo.

Sample Scores

very basic:

   rtsetparams(44100, 2)
   load("MULTEQ")

   rtinput("mystereofile.wav")

   inskip = 0
   dur = DUR()
   amp = 0.5
   bypass = 0

   type1 = "lowshelf"
   freq1 = maketable("line", "nonorm", 100, 0,100, 1,100, 3,1000)
   Q1 = 10
   gain1 = maketable("line", "nonorm", 100, 0,6, 1,6, 3,-6)
   bypass1 = 0

   type2 = "highshelf"
   freq2 = 2000
   Q2 = 5
   gain2 = maketable("line", "nonorm", 100, 0,-12, 1,9, 2,0)
   bypass2 = 0

   MULTEQ(0, inskip, dur, amp, bypass, type1, freq1, Q1, gain1, bypass1, type2, freq2, Q2, gain2, bypass2)

See Also

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