What You Should Know About Using Reverbs
The use of reverb as a mean to create space and depth in the mix is a fundamental subject that concerns most of us dealing with music production activities. The use of this audio processing effect can on one hand significantly enhance the mix. On the other hand the poor use (or abuse) of it can have a detrimental effect on the final track. Thus, it is key to understand what a reverb is, how it operates on the audio material and how to design the appropriate settings to support what we look after.
1. What is a “Reverb”:
Let’s start by saying that reverb is an electronic reproduction of echo, which leads to the definition of “Reverberation”. Now the real mechanism in which reverb acts is much more complex than just an echo (i.e. repetition of a sound after a given delay). The Reverb will actually reproduce a combination of thousands of repetitions which occur at different timings, some of them below 0.1 seconds. The sound envelope generated by a reverb output can be split up in three different phases:
Early Reflections: For any direct sound created, there will early reflection created by nearby physical barriers hit by the direct sound first, such as a side wall. Since these reflections are considered to be closer to the direct sound source, the sound emitted will be heard before the main reverberation bulk sounds, and will also have the highest amplitude. This sound phase is typically between 1 millisecond to 35 milliseconds. Body: Main Sound block coming off the reverberation from all physical barriers in the sound space. Depending on the size of the simulated space, the body phase duration can range between 30-35 milliseconds to longer durations such as 4 seconds or more. Decay: This would be considered the last tail of the reverb sound as it drops below a given threshold (typically from 50dB to 70 dB). While there is not clear cut among the phases described above, yet, if analyzing a sound wave off a reverb output we should see the demarcation in between the above based off the shape of the sound waveform.
2. Types of Reverb:
As we are looking at different reverb situations a reverb wave form will be dependent on sound room space characteristics. For example a sound reverb simulating reverberation in a hall will behave differently than the one emitted in a closed room. Also, different materials of the sound barriers create a significant difference on how the sound is reflected and the amount of sound absorption the materials has. A metal surface will reflect sound back at a higher reflection rate than wood, etc.
Practically speaking there are 5 generic categories of reverb types:
Spring and Plate reverbs have been artificially created by simulating reverberation of sound on either spring or metal plates. Some of them simulation of man-made reverb devices in the ‘60s.
3. How We Use Reverb in Our Mixes
So now the question is how I use a reverb properly in the mix. But even before that we must answer: What should we be applying reverb to?. There are several options depending on the stage of the mix and the intent of the reverb. But we have three most common alternatives:
Apply reverb directly to a single track (or instrument). This also includes the option to split up the signal and apply reverb only to one of the splits by using an auxiliary bus, and leaving the dry signal split come out through directly from the track output. In this case we look at the way we would like to produce ambiance from the sound emitted by that particular instrument. Keep in mind that 100% dry sound is not physically possible in reality: Everyone listening to an instrument will not only perceive the direct sound but some sort of reverberation coming from the surrounding. I. If you are placed closed to the instrument, then the ratio between the direct sound and reverberation will be much larger. So if your mix dictates that we would need to have an instrument with presence (such as a lead instrument), you will probably want to cut off on reverb time to avoid sending the instrument back to the virtual stage in your mix.
II. As shown above, it’s the reason why lead instruments get all the benefits of using “Delays” as opposed to a straight Reverb. The delays will prevent the muddiness created by a reverb sound envelop on top of the direct sound, but they will still provide depth by the wet signal. As we can see “Delay” is a particular type of reverb which only has one echo occurring after a specified amount of time. The way the signal is processed is by just repeating the original signal shifted by the delay time. Delay times used in lead instruments can vary between 35 msec all the way to 400 msec. The rule is if you can hear it clearly in the mix, you should probably cut the delay time by ¼ of original value and/or the wet/dry signal ratio.
III. One of the known tricks to use reverbs in lead instruments and avoid muddiness is to set a pre-delay (typically around 35 – 45 msec) to separate the dry signal from the wet signal.
Apply reverb to a group of instruments. For example we may choose to apply a single reverb to a drum kit in which we would have several toms and a snare. This case is used when we are interested in simulating a single sound reverb in a room coming from the same source (i.e. the drum kit). This also would save DAW resources as the reverb will be shared by the different tracks affected by the Reverb. In order to accomplish this we would typically send the signals from the different tracks to an auxiliary bus and apply the Reverb there at 100% Wet. Then the ratio between dry and wet signal is given by the output levels of the individual tracks dry signals outputs and the Reverb bus output. Apply reverb to the overall mix: This option is typically used in the Mastering stage (if required) and it looks for a final master production technique to create overall depth and space to the whole mix. This is typically used very lightly in a way that the reverb itself is not perceived as a standalone effect but just provides a different characteristic to the mix. This is particularly important in order to avoid the reverb becoming the main cause of a harsh, muddy or spacey mix. The second very important aspect is to apply reverb in order to provide a specific nature to the mix such as natural, dark, bright, metallic, etc, which mostly depends on what we are after when producing the track.
4. Reverb Setting Guidelines
Bass and Kick Drum should be set at 100% Dry. Use less reverb in snare than in other drum kits (Cymbals and Toms). A gate- Reverb is a good idea for a snare in order to have presence and to fatten its sound. Lead instruments with attack: Use Plate reverbs with pre-delays setting, or just a delay or a combination between a short reverb and delay used by splitting up the signals to hard left and hard right panned buses with slightly different delay time settings each. Strings or strings-synth simulated sound can benefit from using Hall reverbs, depending on their function in the mix. For background and ensemble function a hall reverb at about 1500 msec to 2500 msec can work well. Drums HiHat: I typically use a room reverb at 20-30 msec about 20% wet. As a general rule the reverb can also contribute to a specific tonality of the track. You can control its output tonality by filtering out undesired frequencies in the wet signal. For example if you would like to avoid an instrument sounding too brittle, you might want to filter some of the high ends frequencies on the wet signal. Remember that all these are ball park ideas but in no means represent a generalization. The mixing engineer needs to look at the intent of the mix and/or a particular track to come up with what is appropriate for the situation.
5. Consideration for the Use of Convolution Reverbs
Convolution reverb is a process used for digitally simulating the reverberation of a physical or virtual space through the use of software profiles. It is based on the mathematical convolution operation, and uses a pre-recorded audio sample of the impulse response of the space being modeled. To apply the reverberation effect, the impulse-response recording is first stored in a digital signal-processing system. This is then convolved with the incoming audio signal to be processed. So in other words, this type of reverb is a room simulator based upon actual signals samples. Audio effects plugins such as SIR2, AltiSpace and similar are software which generate convolution reverbs. In order to be able to use them you should have a convolution reverb impulse library.
Since these audio signal processors are based upon a pre-sampled room reverb signal, the shape of the overall effect is given but you can change the envelope parameters to adjust to your needs such as Envelope time, pre-delay, stretch, etc. I am very fond of these types of reverbs since they much more accurately represent what a real sound reverberation process should be from a specific room environment perspective. This would avoid the situations in which we create a reverb signal using the standard simulations which is not physically possible to occur in reality. The second advantage of these processors is such that it doesn’t require the skills to dial the settings. Most cases, we pick up the right convolution reverb impulse in our library and make small adjustments to it. If you are looking for convolution reverb impulse resources visit some of these sites: