FFT-based delay processing.
in RTcmix/insts/jg/SPECTACLE2
SPECTACLE2(outsk, insk, indur, OUTAMP, INAMP, ringdowndur, fftsize, windowsize, WINDOWTABLE, overlap, EQTABLE, DELAYTABLE, FEEDBACKTABLE[, MINEQFREQ, MAXEQFREQ, MINDELAYFREQ, MAXDELAYFREQ, BINMAPTABLE, WETDRYMIX, inputchan, PAN])
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 | output amplitude multiplier | relative multiplier of input signal | yes | no | |
| p4 | input amplitude multiplier | relative multiplier of input signal | yes | no | |
| p5 | ring-down duration | seconds | no | no | |
| p6 | FFT length | samples, power of 2 | no | no | usually 1024 |
| p7 | window length | samples, power of 2 | no | no | usually FFT length * 2 |
| p8 | window table | reference to pfield-table handle | yes | no | zero for internally generated Hamming window |
| p9 | overlap (FFT window overlap) | positive 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; higher overlaps use more CPU |
| p10 | EQ table (i.e., amplitude scaling of each band) | dB | yes | no | in dB (0 dB means no change, + dB boost, - dB cut) |
| p11 | delay time table | seconds | yes | no | |
| p12 | delay feedback table | multiplier, 0-1 | yes | no | |
| p13 | minimum EQ frequency | Hz | yes | yes | default: 0 |
| p14 | maximum EQ frequency | Hz | yes | yes | default: Nyquist |
| p15 | minimum delay frequency | Hz | yes | yes | default: 0 |
| p16 | maximum delay frequency | Hz | yes | yes | default: Nyquist |
| p17 | bin-mapping table | - | yes | yes | default: 0 (no mapping done) |
| p18 | wet/dry mix | 0: dry -> 1: wet | yes | yes | default: 1 |
| p19 | input channel | - | no | yes | default: 0 |
| p20 | pan | 0-1 stereo; 0.5 is middle | yes | yes | default: 0 |
Parameters labled as Dynamic can receive dynamic updates from a table or real-time control source.
Author: John Gibson, 6/12/05
The SPECTACLE2 instrument is an evolution of the earlier SPECTACLE instrument. It allows the user to delay different parts of the spectrum of a signal at different rates, leading to some very interesting echoey-bizarro effects. Try it! It’s fun!
It is probably a good idea to know in general terms how FFT analysis/synthesis DSP operates.
Although they are listed as taking references to pfield table-handles only, it is possible to update the p10 (“EQTABLE”), p11 (“DELAYTABLE”) and p12 (“FEEDBACKTABLE”) tables dynamically using modtable(table, “draw”, …). If any of these are not tables, then the single constant or changing values will apply to all FFT bins. (Useful if you want all bins to use the same feedback, for example.)
Output begins after a brief period of time during which internal buffers are filling. This time is the duration corresponding to the following number of sample frames: window length - (fft length / overlap). This duration is called “latency duration” below.
Most updateable parameters begin at the start of the note, including the initial latency duration when the instrument plays silence, and act until the end of the note, including the ring-down duration. The exception is the input envelope. It begins after the latency duration and controls the time span given by p2 “indur”).
The way the frequency range between p13 (“MINEQFREQ”) and p14 (“MAXEQFREQ”) and the delay frequency range (p15, “MINDELAYFREQ” and p16, “MAXDELAYFREQ”) operate with the various tables (including the delay feedback table, p12) is a little complicated:
If you use the bin-mapping table (p17), it must be the same size as the EQ and delay tables (p10-12). If the sum of all the elements of the mapping table is less than the total number of FFT bins – which is (FFT size / 2) + 1, and includes 0 Hz and Nyquist bins – then the extra higher-frequency bins will be assigned to the last control table element. If the sum of mapping table elements is greater than the number of bins, then some higher-frequency bins will be omitted. The frequency ranges discussed in note 3 are ignored when using the bin-mapping table. Don’t you wish you had passed zero here to ignore this feature?
SPECTACLE2 can produce either mono or stereo output.
very basic:
rtsetparams(44100, 2)
load("SPECTACLE2")
rtinput("mysound.wav")
inchan = 0
inskip = 0
indur = DUR()
ringdur = 15 // play after indur elapses, while delay lines flush
amp = 0.4
wet = 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)
window = 0 // use Hamming window
// input envelope (spanning )
ienv = maketable("line", 1000, 0,0, 1,1, 19,1, 20,0)
// output envelope (spanning + )
oenv = maketable("curve", 1000, 0,1,0, 2,1,-1, 3,0)
eqtablen = fftlen / 2
mineqfreq = 0
maxeqfreq = 0
// EQ curve: -90 dB at 0 Hz, ramping up to 0 dB at 200 Hz, etc.
eq = maketable("line", "nonorm", eqtablen, 0,-90, 200,0, 8000,-3, 22050,-6)
deltablen = fftlen / 2
mindelfreq = 0
maxdelfreq = 0
// fixed delay times between .4 and 3, randomly spread across spectrum
min = .4
max = 3
seed = 1
deltime = maketable("random", "nonorm", deltablen, "even", min, max, seed)
// constant feedback of 90% for all freq. bands
fb = .9
// do it for the left chan
SPECTACLE2(0, inskip, indur, amp * oenv, ienv, ringdur, fftlen, winlen,
window, overlap, eq, deltime, fb, mineqfreq, maxeqfreq,
mindelfreq, maxdelfreq, 0, wet, inchan, pan=1)
// shift delay table to decorrelate channels
deltime = copytable(modtable(deltime, "shift", 2))
// do it for the right chan
SPECTACLE2(0, inskip, indur, amp * oenv, ienv, ringdur, fftlen, winlen,
window, overlap, eq, deltime, fb, mineqfreq, maxeqfreq,
mindelfreq, maxdelfreq, 0, wet, inchan, pan=0)
slightly more advanced:
// This shows how to "draw" randomly into the delay time table. This
// is an experimental feature, so don't rely on it yet. -JGG, 6/22/05
rtsetparams(44100, 2)
load("SPECTACLE2")
bus_config("MIX", "in 0", "aux 0 out")
bus_config("SPECTACLE2", "aux 0 in", "out 0")
bus_config("SPECTACLE2", "aux 0 in", "out 1")
rtinput("mysound.wav")
indur = 60
ringdur = 10
dur = DUR()
amp = 0.2
for (st = 0; st < indur; st += dur)
MIX(st, 0, dur, amp, 0)
// ========================================================================
indur = st
wet = 1 // 100% wet
fftlen = 512 // yielding fftlen / 2 frequency bands
winlen = fftlen * 2 // the standard window length is twice FFT size
overlap = 2 // 2 hops per fftlen (4 per window)
window = 0 // use Hamming window
// no EQ
mineqfreq = 0
maxeqfreq = 0
eq = 0
// delay time -------------------------------------------------------------
mindelfreq = 0
maxdelfreq = 0
deltablen = 12 // changing this makes a big difference
deltimeL = maketable("literal", "nonorm", deltablen, 0)
deltimeR = copytable(deltimeL)
// left chan
randfreq = 9.5
seed = 1
index = makerandom("even", randfreq, min = 0, max = deltablen, seed)
value = makerandom("even", randfreq, min = 0.01, max = 5, seed)
value = makefilter(value, "smooth", lag = 30)
deltimeL = modtable(deltimeL, "draw", "literal", index, value, 0)
// right chan
randfreq = 9.0
seed += 1
index = makerandom("even", randfreq, min = 0, max = deltablen, seed)
value = makerandom("even", randfreq, min = 0.01, max = 5, seed)
value = makefilter(value, "smooth", lag = 30)
deltimeR = modtable(deltimeR, "draw", "literal", index, value, 0)
// ------------------------------------------------------------------------
// set feedback and overall gain using mouse
fb = makeconnection("mouse", "x", min=0, max=1, dflt=0, lag=50, "feedback")
amp = makeconnection("mouse", "y", min=-60, max=6, dflt=0, lag=50, "gain", "dB")
amp = makeconverter(amp, "ampdb")
SPECTACLE2(start=0, inskip=0, indur, amp, iamp=1, ringdur, fftlen, winlen,
window, overlap, eq, deltimeL, fb, mineqfreq, maxeqfreq, mindelfreq,
maxdelfreq, 0, wet, inchan=0, pan=1)
SPECTACLE2(start=0, inskip=0, indur, amp, iamp=1, ringdur, fftlen, winlen,
window, overlap, eq, deltimeR, fb, mineqfreq, maxeqfreq, mindelfreq,
maxdelfreq, 0, wet, inchan=0, pan=0)
CONVOLVE1, LPCPLAY, PVOC, SPECTACLE, SPECTEQ, SPECTEQ2, TVSPECTACLE, VOCODE2, VOCODE3, VOCODESYNTH