Audio Effects 101: Time-based FX
Time-altering audio effects like reverbs, delays and choruses all function in essentially the same way: they capture a portion of an input sound, delay it slightly, then play it back. The main differences between the various types of time-based audio effects lie in the lengths of time for which they delay the sound, as well as in the complexity of the resulting delays.
Reverb may be the most important audio effect in the producer’s arsenal. A reverb plug-in analyzes an input sound, creates a series of echoes from it, then blends the resulting echoes with the input sound. The first set of echoes that the reverb produces is the “early reflections”; the later echoes are the “tail.” Transparent reverb configurations simulate listening to the sound in a physical space; more extreme reverberation settings can be used creatively to alter sounds until they’re unrecognizable. Apart from specialized units like spring and inverse plug-ins, reverbs are usually categorized by the type of physical environment they emulate:
Hall reverbs produce the longest series of echoes. These plug-ins simulate a large listening space like a concert hall or auditorium. Use a hall reverb when you want to push sounds all the way to the back of the mix, or to produce a washed-out, chillwave-style effect.
Room reverbs simulate smaller listening spaces than hall units. These virtual environments can range from a club to a closet, making room reverbs the most useful and versatile type of reverberation effect.
Plate reverbs don’t simulate a three-axis space at all. Instead, they emulate the effect of bouncing a sound off a sheet of metal placed in front of the sound source. Plates have very short echo times, making them useful for sounds (like the lead vocals and guitars) that need a bit of smoothing and atmosphere, but that you don’t want to bury in the mix. A spring reverb works on the same principle, but emulates a coiled spring instead of a flat plate.
Reverbs are also categorized by the way that they produce echoes. An algorithmic reverb uses a mathematical equation to calculate the position and volume of the echoes, while a convolution reverb loads a model of an actual physical space (in the form of an impulse response), then uses this model to produce the echoes. These categories overlap with the previously-mentioned divisions: you can have a convolution room reverb, or an algorithmic plate reverb, for example. Convolution reverbs produce more natural-sounding echoes, but use more CPU power than algorithmic plug-ins.
Like reverbs, delay effects push a portion of the input sound into the future by delaying its playback. While reverbs create a complex series of echoes, however, delays are usually much simpler. It’s often possible to make out the individual echoes that a simple delay produces, whereas a reverb’s echoes are smoothly blended together.
A delay plug-in has two main controls: time and feedback. The time control sets the length of time by which the plug-in delays the sound; many delay units can synchronize this setting to correspond with a note value. The feedback settings determine how much of the output is cycled back into the delay’s input. A low feedback setting creates a simple, dry delay; a high level of feedback makes a long, dub-style delay loop.
There are a few specialized types of delay you might also run into:
A ping-pong delay incorporates two delay units, one for the right channel of audio and one for the left. By switching the audio between the two, the plug-in creates a “bouncing” effect as the audio moves from one channel to the other and back.
Filter delays incorporate one or more filters that allow you to apply the delay to certain parts of the frequency spectrum. Using a filter delay, you can, for example, apply a delay to the high frequencies in a sound, leaving the lower frequencies unaffected. Some filter delays include separate filters for the left and right audio channels, allowing you to incorporate a ping-pong effect.
Grain delays slice the input audio into extremely short segments, then delay each slice by a slightly different time. Most granular delays also incorporate pitch-shifters, which allow them to change the pitch of each slice. Granular delays are the most complex delay plug-ins, and can warp and mangle audio into a completely different sound.
A chorus effect produces a very short, tight delay, then modulates the pitch of the delayed sound with an LFO. Use a chorus effect when you want to make an element of your track thicker and fuller without using an obvious delay. Chorus plug-ins work best on vocals, lead instruments, bass tracks and other elements that you want to keep in the front of the mix.
A flanger, which is very similar to a chorus, delays the left and right audio channels by very slightly different amounts. This puts the two channels just out of phase with each other, creating a slight whooshing effect. A flanger is very similar in effect to a phaser (which, however, modifies the frequency spectrum rather than the timing).