RTcmix - Reference

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REVERBIT -- modified basic Schroeder reverb
in RTcmix/insts/jg

quick syntax:

REVERBIT(outsk, insk, dur, AMP, RVBTIME, RVBAMT, chan0delay, FILTFREQ[, dcblock, ringdowndur])

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.

   p0 = output start time (seconds)
   p1 = input start time (seconds)
   p2 = input duration (seconds)
   p3 = amplitude multiplier (relative multiplier of input signal)
   p4 = reverb time (seconds, > 0)
   p5 = reverb amount (0: dry --> 1: wet)
   p6 = right channel delay time (seconds, > 0)
   p7 = cutoff freq for low-pass filter (Hz, 0 will disable filter)
   p8 = apply DC blocking filter (0: No, 1: Yes) [optional; default is 1]
   p9 = ring-down duration [optional; default is p4)

   p3 (amplitude), p4 (reverb time), p5 (reverb percent) and p7 (cutoff)
   can receive dynamic updates from a table or real-time control source.

   Author:  John Gibson, 6/24/99 rev for v4, 7/11/04
   based on original code by Paul Lansky

REVERBIT reverberates the input signal using a variation on a typical Schroeder network of comb and allpass filters.

Usage Notes

REVERBIT is a very old reverbator (dates back to the late 1970's). For a more general reverberation algorithm the FREEVERB or GVERB instruments are probably better. There are also a number of excellent room-simulator instruments (listed under the See Also section below).

Here's how REVERBIT works:

(1) Runs the input signal into a simple Schroeder reverberator, scaling the output of that by the reverb percent and flipping its phase. (The reverberator has four comb filters in parallel, followed by two allpass filters in series.)
(2) Puts output of (1) into a delay line, length determined by "chan0delay" (p6).
(3) Adds output of (1) to dry signal, and places in left channel.
(4) Adds output of delay to dry signal, and places in right channel.
(4) Feeds output to optional lowpass and DC-blocking filters.

REVERBIT works best with short reverb times and a moderate amount of reverberated sound mixed into the output. If you crank "RVBTIME" (p4) and "RVBAMT" (p5), you'll hear a grungy, grainy reverb tail. You can smooth this some using the lowpass filter. Lansky's original intent was just to "put a gloss on a signal,'' not to swamp it with gushy reverb.

The chan0delay parameter (p6) governs the delay time between output channels. A small amount (e.g., .02 seconds) livens up the sound; a larger amount makes an audible slap echo.

The amplitude multiplier (p3, "AMP") is applied to the input sound before it enters the reverberator.

The point of the optional ring-down duration parameter (p9, "ringdowndur") is to let you control how long the reverb will ring after the input has stopped. If the reverb time is constant, REVERBIT will figure out the correct ring-down duration for you. If the reverb time is dynamic, you must specify a ring-down duration if you want to ensure that your sound will not be cut off prematurely.

REVERBIT requires stereo output. The input file can be either mono or stereo. If the input is from a real-time source, such as live audio in or an aux bus, p1 ("inskip") has to be 0.

Sample Scores

   rtsetparams(44100, 2)
   load("NOISE")
   load("REVERBIT")

   bus_config("NOISE", "aux 0 out")
   bus_config("REVERBIT", "aux 0 in", "out 0-1")

   totdur = 7
   for (st = 0; st < totdur; st = st + .3)
      NOISE(st, notedur=.1, amp=20000)

   REVERBIT(outskip=0, inskip=0, totdur + notedur, amp=1, revtime=.6, revpct=.4, rtchandel=.02, cutoff=5000)