Weird reverb

admin: First posted on 2007 08 29

In an attempt to get some interesting sounds out of a reverb, whether useful or not, I decided to experiment. To give credit where credit is due, I did spend some time reading articles on harmony-central.com about various properties of what I would consider non-natural reverbs.

I started CoolEdit Pro, opened a wave file containing a single instrument track and applied a reverb to it. I turned the dry mix (the original non-reverberated sound) down to zero, thus effectively producing a track that contained only the reverberated portion of the final signal and none of the original signal. This was a track of a nylon string acoustic guitar with a very pronounced initial pick attack / accent and very much of a short ringing sustain.

The end result of this experiment was not very interesting. It sounded just like the original track, but ugly. I had forgotten how pronounced the pick was and did not think of the fact that when that pick shows up in the reverb the result is just another guitar track. What was interesting was that I had a reverb track that I can mangle to create something new.

Reverb with gate thresholds

I wanted a very pronounced reverb, but one which cuts off quickly rather than decaying smoothly. Why? Who knows? Partly I was thinking about the gated reverbs described in Harmony Central. Partly it was because I was listening to Slayer’s "Overt Enemy" from "Diabolus in Musica" and it sounded to me as if it had just that type of reverb (which may or may not be true). In any case, I put the original track next to the reverb track and gated the reverb track. The gate was an expander with the following properties:

Flat (1:1 ratio) above -30 dB
5:1 expander below -30 dB

The expander had the following effect: When the signal got below -30 dB, it was attenuated (decreased with a ratio of 5:1; in my recording it practically disappeared). The reverb sounded for a little while and then it is suddenly disappeared. Thus, I got a reverb with a gated decay threshold. To be sure, the parameters of the gate depended on the track and in my case were specific to the acoustic guitar. I rounded the numbers above a bit just to make my point easier.

Reverb with gated times

What I really wanted to experiment originally with was not a gate threshold but gated time. Rather than cutting off the reverb based on an amplitude threshold I wanted to cut it off based on the amount of decay time. For example, I want the reverb to be cut off 250 ms after it starts for each of the notes played, independently on when note amplitudes get to a threshold.

I did not really have a way of doing this directly in CoolEdit, but I could come close. The only reason a gated threshold cuts off at different times is that the track has certain dynamics – some notes and their reverb are louder than others. If all notes were at the same amplitude level and produced a similar sustain, this problem would not exist. The threshold will always come in at the same time and hence the reverb will always be cut off or attenuated at the same time (for example, 250 ms after its start).

The goal then was to make the original non-reverberated sound more even and the best way to do that was compression. The compression I chose was:

8:1 compressor above -25 dB
Flat (1:1 ratio) below -25 dB

This seemed to do the trick, making a very non-dynamic sounding acoustic guitar. To get the gated decay time then, I just applied the same gated threshold as above.

One thing I am beginning to realize is that gated reverbs, as unnatural as they are, are very commonly used. I would have expected a lot of gate reverbs on drums, but not much on anything else. I guess there are a lot of people out there trying to make "eerie" music. You can look around on the internet for the infinite number of reverb units and software pieces made that offer gates in their reverbs. Gates can actually be very complicated and so I cannot really cover all combinations. Gates have attacks, releases, multiple thresholds, and so on. The gated reverb can then also become complex. The two examples above though should be sufficient to get an idea of what gated reverbs sound like.

Predelay and preverb

While we are on the topic of weird reverbs, suppose that you are trying to create a reverb that, rather than decaying after the original signal, builds up to the original signal. Harmony-central.com will call a preverb a "reverse reverb". Now I really have no good way of producing this one using CoolEdit Pro. To test it out, however, one thing I can do is record a simple repetitive sound. I can play, for example, the open first string E over and over again with unchanging tempo. Then I can take the recorded wave, get its reverb with zero percent dry mix as before, reverse the reverberated wave, and mix it back with the original non-reverberated one, with some adjustment in time. CoolEdit Pro does not actually have the functionality to reverse a wave, but an algorithm to do that can easily be written.

Reverb in "space"

Reverb is really a spatial phenomenon. It seems useful to me to try and accentuate or modify how the reverb works in the physical space.

Just for the sake of the experiment, why not bounce the reverb left and right to see what happens? If you get the bouncing tempo right the effect is interesting, even though after a while it gets annoying. It is better to just bounce an echo.

A better thing to do is to differentiate between the reverbs applied to the left and right channels. I was trying to experiment with a reverb which is has larger length but smaller original signal mix in the right channel. For example, I was trying a reverb with 1250 ms total length on the right, but 1100 ms total length on the left with minor changes in the dry mix. The result is interesting. It is thicker and gives a better spatial position to the listener (rather than the instrument itself). The only problem is that it sometimes sounds "phased", which could be just CoolEdit Pro.

Why?

Why are these reverbs interesting? It is difficult for me to say, mostly because I have no good way of implementing all of them. It seems to me that gated reverbs and reverse reverbs would works well sparse tracks that follow the tempo well, such as snares and distorted riff guitars with good sustain. Irregular reverbs on the other hand are natural. They are interesting to me as they seem to displace the listener from the center of the music piece, which has its own applications.

Our first album had a song which we deemed (jokingly) to be an "acid jazz" song. It was basically a slow heavy drums and bass song layered with bizarre guitar solos and talking voices. This is the only song so far on which I experimented with a gated reverb and that mix did not make it in the final album. I slapped a very pronounced reverb on the mix and then compressed the result. It made the song distinctly thumping, which worked out well for an eerie song like this.

authors: mic