Introduction to reverb
Reverb allows you to create a sense of space to an audio recording. It is used to recreate spaces which were not there during the recording process. This gives creative freedom to recreate all kinds of acoustic spaces. The reason that digital reverb is usually preferred over natural reverb is that it is much cheaper, it’s easier to tweak the reverb parameters and it offers more control with a lot of scope for creative freedom. It requires a great deal of time and experience to obtain good quality recordings using natural reverberation due to the fact that you need to be precise in selecting the right recording environment, microphones and optimum microphone placement techniques. Also, once you record wet, the reverb gets printed along with the main audio signal and it’s hard to get back the dry audio signal.
In modern era multi-track recordings, musicians and singers often record their parts at different times and possibly in different studios around the world. Since such productions rely heavily on overdubbing, reverb is very useful as it helps in blending different instruments and voices making it feel as if they were all recorded together in the same acoustic space. Reverb can be generated artificially by using either digital technology or analogue reverb units. With artificial reverb, the amount of reverb being sent to each individual instrument or voice can be tweaked independently. Hence it allows the music producers to wait until mixdown before they commit to a particular reverb setting for every instrument.
Use of the right amount of reverb and the right decay time is important. Applying too much reverb on a sound can make the overall mix muddy. The clarity of instruments is lost when you apply too much reverb. One trick many producers use is to equalize or filter the reverb such that only certain frequencies of the reverb are sent to the dry signal. For example, if you apply a High Pass Filter on your reverb device around 600 Hz and send only the higher frequencies to your dry audio signals, it will ensure that the low end does not get cluttered with unnecessary resonances. Apart from Equalization of the reverb send, you can also use plenty of other devices in the chain of effects that process the reverb, which are intern sent to the audio signal.
Reverb could be created using either digital technology or analogue reverb processors. While both are used in the music industry, digital reverbs are gaining popularity over the years. Good quality reverb is quite an essential part of a good audio mixdown. Digital reverbs employ the use of mathematical algorithms or sampling of hardware reverb units to generate sound. Some of the good digital reverbs available today are Lexicon, Sony Oxford, Vallhalla, Yamaha and Altiverb. Microprocessors are used to store and delay the recall of the signal thus simulating the reflection of the sound. Although this task may appear simple, it is not easy to attain a very realistic reverb. This is because the reflections need to be mapped accurately and reproduced just as accurately. The parameters of the reflections also must be controllable so that the settings can be tweaked as per the requirement.
Before getting into the types of reverb, we can first have a look at the parameters that you can adjust on your reverb.
Ratio of Dry/Wet signal: This parameter is used to adjust the amount of reverb that is being sent to the audio signal. 100% dry means that the signal is not affected with reverb. 100% wet means that the signal is affected with reverb to the maximum extent. A good option is to take the 100% wet setting on the reverb and then send the reverb to the audio signal as a ‘send’ where you can decide how much reverb to apply to blend with the dry signal.
Decay Time: The time it takes for a reverb signal to die out is the decay time. Open places have a shorter decay time and closed spaces have a longer decay time. The dimensions of the room, the material and the thickness of the walls, floor and ceiling are the main parameters that decide the decay time. An increased inside surface area reduces the decay time. This implies that when a concert hall is completely full or when a movie theatre is houseful, the decay time will be shorter than the corresponding spaces if they were empty. It is a common practice to set reverb decay time and predelay time according the speed of the track.
60,000 divided by BPM (Beats Per Minute) = delay or reverb time (quarter notes)
Using this technique with different reverbs, delays, and then varying send levels of the different elements within your mix will glue the mix together while still giving each element it’s own sonic space within the mix.
Early Reflections: They arrive later than the direct sound, usually about 5 to 100 milliseconds after the direct sound. However, they can arrive before the onset of full reverb. Early reflections subconsciously give the brain information on the size of the room, the materials with which the room was constructed and a sense of distance of sounds in a room. This creates a mental image of a corresponding acoustic space that our brain can recognize such as an open field or a church or a room and so on.
Predelay: Predelay is the amount of time between the original dry sound and the audible onset of early reflections. Early reflection combined with predelay is quite useful to create depth in your sound.
Density: Density of a reverb refers to the number of reflections in the reverb tail. Increasing the density will make the reverb sound more warm and natural. Reducing it can create a grainy sound, which can be used for effects.
Types of reverb
Room: Rooms have low decay times, typically between 0.2s and 1s. Rooms are usually not very huge, hence even the predelay and early reflection times will be low. For example, using a room reverb on a dialogue track will give the impression of a person speaking in a room. This technique is used in film sound.
Chamber: Chamber reverbs are used on orchestral instruments to give the impression of a chamber orchestra. The reverbs imitate the wooden construction with precise decay times and early reflections. This results in a warmer tone, especially for a strings section. In some cases, it is used on drums as well.
Hall: Hall reverbs mimic the construction of a concert hall, where the reverb time is anywhere between 1s to 4s. They have a characteristic tone of dense early reflections, followed by a long decay time. Since concert halls were used to perform orchestral pieces, much of modern music now still uses these tools to mimic that sound for certain instruments and sections. Hall reverbs also work really well on lead vocals and percussions, giving them a rounded tone.
Plate: Hall, room, and chamber reverbs mimic an actual space. However, some reverbs try to achieve a different effect, namely the plate and spring reverbs. The plate reverb is essentially the reverberation caused when the sound source hits a metallic plate. Plate reverbs are famous for getting to the density of the reverb quicker than the other types, are are frequently used on vocals.
Spring: Spring reverbs are known for their characteristic metallic texture, which is due to the sound source travelling through a spring. These have been used extensively on different types of guitars. They also help in getting a warm vintage vocal tone. Sometimes, spring reverbs are used on woodwinds to make the sound fatter.
Convolution reverb uses samples of real spaces to apply reverb to a sound. This is done by the method of recording an impulse response also known as I.R. In this process, the dry sample is used in phase inverted form to cancel out the same sound present within the reverb tail, meaning that you're left with a recording of the space in question which can then be applied to your mix. However, since reverb depends a lot on the tone and timbre of the sound that was recorded, choosing the right sound for recording the impulse response is very important. For example, if you were to record a bass guitar in a church, you would have a huge warm reverb tail with more low frequencies than high. On the other hand, if you were to record a violin, the impulse response would have a tighter reverb with the lower frequencies muffled and more of the higher frequencies being enhanced. The impulse response also varies with a change in the envelope of the sound being recorded. For example, if you were recording high hats or shakers or any other percussive sound, they would have a different kind of reverb tail than a sustained sound like that of a flute or violin playing a legato piece. A few good digital convolution reverb plugins are SIR Audio Tools SIR2, LiquidSonics Reverberate, Audio Ease Altiverb 7, and Logic X's Space Designer.
Applications of reverb
Reverb can be applied to different elements of a song in many ways. For warm vocals, a reverb with high density, medium decay time and low-medium pre-delay often works well with plate reverbs.
In songs, not all elements are in the front. Some are pushed back to help support the elements in the front. Reverb plays a vital role in achieving this effect. By tweaking the parameters, supporting instruments can be sent backwards, which creates depth in the song. The type of reverb can change the depth amount greatly. For example, mono spring reverbs are used on vocals to give a reverb effect, but they don’t push the voice backwards in the mix.
Reverb can be used in many creative ways. Gated reverbs, reverse reverbs are widely used in mainstream electronic and pop music.
Reverse reverb: Reverse reverb is an effect created by first applying a reverb on a dry sound and then recording only the reverb without the dry signal. Next the reverb recorded is reversed and then layered with the dry signal. This creates an interesting effect.
Gated reverb: Gated reverb is created by routing the output of the reverb to a noise gate. The amount of reverb coming out of the gate depends primarily on the threshold, hold time and the attack and release settings of the gate. Gated reverb is a standard practice for making the drums sound crisp and punchy in a recording and was discovered by Peter Gabriel. For application on drums, a very fast attack, very fast release would work. The rest of the parameters can be adjusted according to taste, but it’s important to set the threshold carefully so as to avoid artifacts and unwanted pumping effects.
To create ambient vocal pads, adding the reverb as an insert and making it completely wet with medium-high decay time transforms the vocals. Although, it must also be EQ’d properly to make sure it does not interfere with the lead vocals.
Sometimes, to get a dreamy vocal tonality, the reverb is inserted on the track with above 50% dry-wet ratio, a low predelay and high decay time. This effect is used in songs as well as voiceovers.
Artificial reverb has significant use in modern musical productions, especially in genres that have a lot of space effects such as ambient and chillstep music. Lush pads and ethereal drones can be created by taking an audio signal and applying a lot of reverb to it. In this case, the reverb is not used to emulate a real room or hall. It is used to create a musical ambience. Reverb can thus be used in such ways to create a more artistic or creative effect as seen in various commercial records.