After equalization and compression, one of the most frequent effects live sound engineers rely on is reverb. In order to use this powerful tool to its optimum level, it's important to understand some basic concepts.
Reverberation is the continued sound that exists in a room after the source of the sound has stopped. We've all heard it when doing something like clapping our hands (or bouncing a basketball) in a large enclosed space like a gym. All rooms have some reverberation, even though we may not always notice it. The characteristics of the reverberation are a big part of the subjective quality of the sound of any room in which we are located. Reverb is sometimes mistakenly called echo (which is an entirely different phenomenon).
Our brains derive a great deal of information about our surroundings from the sound of a room and its reverberation. Consequently you need to make careful choices when you enhance a room's natural reverberation with electronically generated reverb. Here are some tips to help you keep reverb from muddying up your live sound:
Short reverb decay times (see also RT-60) usually are a better fit for up-tempo songs. Try Room, Gate or Early Reflections programs with a decay time of up to 1.5 seconds. A longer reverb can result in a loss of clarity. Longer reverbs can work better for slow tempo compositions like ballads and ambient mixes. Try a Plate or Hall setting for the best choice. Even economy-priced units usually offer a variety of plate reverbs.
Using EQ on reverb can help control the effect by restricting its bandwidth, to avoid muddying up your sound. "Natural" reverberation typically has a fairly narrow bandwidth, so if you're trying to keep the sensation that you are playing in a real room, use a high-frequency bandwidth of no more than 8 kHz. On bass instruments (kick drum, bass, synth or guitar), for example, try bass roll-off using filters or EQ at around 80-100Hz. This stops them from competing with low-frequency reverberation decay. Remember that when you apply reverb it will affect the listener's perception of the whole mix, not just the instrument you are treating. Unless it's being used as a creative effect in a sparse mix, long reverbs do not work well on bass sounds.
Reverb has a spatial effect on the soundstage as the listener perceives it, by placing voices or instruments near (less reverb) or farther away (more reverb). Make sure that you are creating the right environment for your sound within the context of the mix and the room. Some mix engineers put loads of reverb on the vocals, yet the voices are still at the front of the mix. You can achieve this by using pre-delay, typically 45-120 ms, to distance the dry sound from the effect. Vocal reverbs with a full bandwidth will emphasize sibilance, so be careful about too much high-frequency signal! Some higher end units, such as the Eventide Eclipse for just one example, provide reverb with full EQ control over individual channels, plus other effects.
