FFT-based delay processor.

in RTcmix/insts/jg/SPECTACLE

quick syntax:

SPECTACLE(outsk, insk, dur, amp, ringdowndur, fftsize, windowsize, windowtype, overlap[, sigmix, inputchan, pan])

NOTE: This is an older RTcmix instrument, the newer SPECTACLE2 instrument is probably better to use.

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 no no  
p4 ring-down duration seconds no no  
p5 FFT length samples, power of 2, usually 1024 no no  
p6 window length samples, power of 2, usually FFT length * 2 no no  
p7 window type 0: Hamming, 1: Hanning, 2: Rectangle, 3: Triangle, 4: Blackman, 5: Kaiser no no  
p8 overlap - how much FFT windows overlap samples, any power of 2 no no 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 wet/dry mix 0: dry -> 1: wet no yes default: 1
p10 input channel - no yes default: 0
p11 pan 0-1 stereo; 0.5 is middle no yes default: 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). Function table 4 is the delay time table. Function table 5 is the delay feedback table. Values > 1 are dangerous!

Author: John Gibson

SPECTACLE is an FFT-based delay instrument inspired by the totally awesome Spektral Delay plug-in by Native Instruments (but minus the interactive ability and some other stuff).

NOTE: This is an older RTcmix instrument, the newer SPECTACLE2 instrument is probably better to use.

Usage Notes

SPECTACLE is not quite like the current PVOC, though obviously related. Basically, each FFT bin gets fitted with its own recirculating delay line, and the delay times and feedbacks are controlled by makegens. For example, if you randomize the delay times, you get wild repetitive, spectrally splintered patterns.

Several makegen function tables control EQ, delay time, and delay feedback (tables 3, 4 and 5) for all the frequency bands of the FFT. Think of them as curves on a graph with frequency on the x axis and amplitude, delay time or feedback on the y axis.

The “windowtype” parameter (p7) allows you to choose the windowing function used for the FFT analysis. The ‘Hamming’ window is usually used.

Parameter p8 (“overlap”) can also be negative powers of 2, e.g., .5, .25, .125, etc. This leaves a gap between successive FFTs, creating ugly robotic effects – beware of clipping.

SPECTACLE can produce either mono or stereo output.

Sample Scores

very basic:

   rtsetparams(44100, 2)

   /* ftp://presto.music.virginia.edu/pub/rtcmix/snd/ah.snd */

   inchan = 0
   inskip = 0
   indur = 2
   ringdur = 15            /* play after indur elapses, while delay lines flush */
   amp = 1
   wetdry = 1              /* 100% wet */

   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  + ) */
   makegen(2, 4, 1000, 0,1,0, 1,1,-1, 2,0)

   /* EQ curve: -90 dB at 0 Hz, ramping up to 0 dB at 300 Hz, etc. */
   makegen(3, 18, 1000, 0,-90, 100,-90, 300,0, 8000,0, 22050,-90)

   /* fixed delay times between .4 and 3, randomly spread across spectrum */
   min = .4; max = 3
   seed = 1
   makegen(4, 20, 1000, 0, seed, min, max)

   /* constant feedback of 80% for all freq. bands */
   fb = .8
   makegen(5, 18, 1000, 0,fb, 1,fb)

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

   /* shift delay table to make right channel sound different */
   shiftgen(4, 500)

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

See Also