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SPECTEQ -- FFT-based EQ
in RTcmix/insts/jg/SPECTACLE


quick syntax:
SPECTEQ(outsk, insk, dur, amp, ringdowndur, fftsize, windowsize, windowtype, overlap[, inputchan, pan])
    This instrument has no pfield-enabled parameters. Parameters after the [bracket] are optional and default to 0 unless otherwise noted.


NOTE: This is an older RTcmix instrument, the newer SPECTEQ2 instrument is probably better to use.


   p0  = output start time (seconds)
   p1  = input start time (seconds)
   p2  = input duration (seconds)
   p3  = amplitude multiplier (relative multiplier of input signal)
   p4  = ring-down duration (seconds, can be 0)
   p5  = FFT length (samples, power of 2, usually 1024)
   p6  = window length (samplse, power of 2, usually FFT length * 2)
   p7  = window type (0: Hamming, 1: Hanning, 2: Rectangle, 3: Triangle, 4: Blackman, 5: Kaiser)
   p8  = overlap - how much FFT windows overlap (samples, any power of 2)
         1: no overlap, 2: hopsize=FFTlen/2, 4: hopsize=FFTlen/4, etc.
         2 or 4 is usually fine; 1 is fluttery; the higher the more CPU time
   p9  = input channel [optional, default is 0]
   p10 = pan (0-1 stereo; 0.5 is middle) [optional; default is 0]


   Because this instrument has not been updated for pfield control,
   the older makegen control envelope sysystem should be used:

   Function table 1 is the input amplitude, spanning just the input duration.
   Function table 2 is the output amplitude, spanning the entire note, including ring-down duration.
   Function table 3 is the EQ table (i.e., amplitude scaling of each band),
      in dB (0 dB means no change, + dB boost, - dB cut).

   Author:  John Gibson



SPECTEQ is an FFT-based EQ/filter, part of the SPECTACLE family of fft-based fun things.

NOTE: This is an older RTcmix instrument, the newer SPECTEQ2 instrument is probably better to use.

Usage Notes

SPECTEQ allows you to directly control the amplitude of each band of an FFT analysis, thus giving you control over the shape of the resynthesized spectrum. This is a very powerful EQ/filter tool.

The parameters are very similar to the SPECTACLE instrument, see the SPECTACLE Usage Notes for more information.

The main thing is to set up function table 3 as the EQ curve. Think of it as an x-axis map of all the frequency bands of the FFT. The y values are then the amount of boost or cut for each FFT band (in relative dB -- 0 dB means no change, + dB boost, - dB cut).

SPECTEQ can produce either mono or stereo output.

Sample Scores

very basic:
   rtsetparams(44100, 2)
   load("SPECTEQ")
   
   rtinput("mysound.snd")
   
   inchan = 0
   inskip = 0
   indur = DUR()
   ringdur = 0
   amp = 5
   fftlen = 1024           /* yielding 512 frequency bands */
   winlen = fftlen * 2     /* the standard window length is twice FFT size */
   overlap = 2             /* 2 hops per fftlen (4 per window) */
   wintype = 0             /* use Hamming window */

   /* input envelope (covering ) */
   makegen(1, 18, 1000, 0,0, 1,1, 19,1, 20,0)

   /* output envelope (covering  + ) */
   copygen(2, 1)

   nyquist = SR()/2
   /* EQ curve: -90 dB at 0 Hz, ramping up to -10 dB at 400 Hz, etc. */
   makegen(3, 18, nyquist/10,
          0,   -90,
        300,   -90,
        400,   -10,
        800,   -20,
       1000,   -90,
       2000,   -90,
       5000,   0,
    nyquist,   -40)

   /* do it for the left chan! */
   start = 0
   SPECTEQ(start, inskip, indur, amp, ringdur, fftlen, winlen, wintype, overlap, inchan, pctleft=1)

   /* do it for the right chan! */
   SPECTEQ(start, inskip, indur, amp, ringdur, fftlen, winlen, wintype, overlap, inchan, pctleft=0)


See Also

CONVOLVE1, LPCPLAY, PVOC, SPECTACLE, SPECTACLE2, SPECTEQ2, TVSPECTACLE, VOCODE2, VOCODE3, VOCODESYNTH