NAME

REVERBIT - reverb instrument

SYNOPSIS

REVERBIT(outskip, inskip, indur, ampmult, revtime, wetpercent, rtchandelay, cutoff [, dcblock ])

Function table 1 gives amplitude curve. This curve (and ampmult) affect the input signal, before it enters the reverberator.

DESCRIPTION

REVERBIT reverberates the input signal using a variation on a typical Schroeder network of comb and allpass filters. (See below for a description of the signal chain.)

This reverb works best with short reverb times and a moderate amount of reverberated sound mixed into the output. If you crank revtime and wetpercent, 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 rtchandelay parameter 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.

REVERBIT uses the curve provided in function table 1 to scale the amplitudes of the input source. Use setline, setexp, or makegen to create function table 1. If this table has not been created, no amplitude scaling (other than that given by ampmult) will occur.

The output of REVERBIT must be stereo. 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, inskip MUST be zero.

SIGNAL CHAIN

Here's how REVERBIT works:

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.)
Puts output of (1) into a delay line, length determined by rtchandelay.
Adds output of (1) to dry signal, and places in left channel.
Adds output of delay to dry signal, and places in right channel.
Feeds output to optional lowpass and DC-blocking filters.

PFIELDS

p0 (outskip) output start time
p1 (inskip) input start time
p2 (indur) input duration
p3 (ampmult) amplitude multiplier (applied to input)
p4 (revtime) reverb time (in seconds, greater than 0)
p5 (wetpercent) percent (from 0 to 1) of wet signal in output
p6 (rtchandelay) right channel delay time (in seconds, greater than 0)
p7 (cutoff) cutoff frequency (in Hz) of lowpass filter applied to output of reverberator (0 to disable filter)
p8 (dcblock) apply DC blocking filter (0: No, 1: Yes) [optional; default is Yes. Turn off for a bit more speed.]

EXAMPLES

Here's a good recipe for a moderate amount of reverb, suitable for enhancing a signal without calling too much attention to the reverb.

   REVERBIT(outskip, inskip, indur, amp=1, revtime=.3,
            revpct=.25, rtchandelay=.015, cutoff=0)

To get a more dramatic reverb effect, it's probably a good idea to roll off the high end graininess, using the built-in lowpass filter.

   REVERBIT(outskip, inskip, indur, amp, revtime=3,
            revpct=.9, rtchandelay=.06, cutoff=1200)

One common use for this instrument is as a sweetener for other instruments. To make this happen, you have to set up an aux bus to send the signal from the first instrument into REVERBIT. It's important to set REVERBIT's outskip and indur so that it catches all the sound output by the first instrument. The inskip to REVERBIT must be zero when reading from anything other than a soundfile.

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

   totdur = 10
   for (st = 0; st < totdur; st = st + .3)
      WAVETABLE(st, notedur=.1, amp=5000, freq=440)

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

AUTHOR

Paul Lansky, revised and documented for RTcmix by John Gibson <johgibso at indiana edu>