Tempo Synced Reverbs
Enhance the natural rhythm of your music & help blend reverbs more naturally using tempo-synced reverb settings
Reverb serves many purposes during the mixdown of a track but many producers and mix engineers alike are unaware of the importance of parameters such as the reverbs pre-delay and decay times in terms of the rhythm of the track. Many producers may not even know what pre-delay is!
Here we explain the fundamentals of reverb and why you should sync it to the tempo of your track
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Reverb Fundamentals
Whilst it may seem complicated at last glance, once a reverberated sound has been split into its component parts. It’s actually very simple to visualise how and why each parameter affects the sound in the way that it does.
there are four main elements to understand with reverberation:
- direct sound
- pre delay
- early reflections
- late reflections
Direct Sound
The completely dry sound. This takes a path from the sound source directly to listener’s ears via the shortest route.
Pre-Delay
The time delay between the direct sound and the first early reflections.
This defines the room size because of the mathematical equation
S=D/T
where:
- S = speed (of sound through air = 343m/s)
- D = distance (in meters)
- T = time (in seconds)
In this case the distance is the time it takes the sound to reach the closest wall and then bounce back to the listener.
The pre-delay is going to take longer to get to the listener’s ears because it has to take an indirect route via one of the walls of the room first. The longer distance travelled means that there will be a slight latency or time delay. This is our pre-delay time.
We as producers may not know the pre-delay time. but if we have an idea of the size of our room (the distance) then we can transpose this formula to get the pre-delay time in seconds T=D/S
This answer can then be multiplied by 1000 to move the decimal place 3 places which converts seconds into milliseconds.
Early Reflections
Early reflections are the first set of distinct echoes caused by sound waves bouncing off of nearby surfaces and room walls.
They will come in a small cluster (one for each wall or surface). The nature of this cluster such as how many reflections there are, how tightly packed they are and their frequency content will depend entirely on the shape and size of the room as well as the location of the sound source and listener within the space.
Generally speaking, tightly packed reflections indicate a small space.
Longer early reflections that are spread out indicate a larger space such as a hall.
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Late Reflections
After the initial early reflections, the sound will carry on bouncing off the surfaces within the room. The sound may reflect, dissipate (be absorbed and lose energy) or diffuse (split and spread in different directions).
How the sound reacts depends on the shape and size of the room, types of surfaces and also what is inside the room.
These characteristics let our brains know the difference between clapping our hands in a tiled bathroom or a cathedral.
When simulating larger spaces, rolling off the high frequencies of the late reflections can lead to a more realistic and natural sound because higher frequencies are more prone to dissipation over a distance due to having much shorter wavelengths, whereas lower frequencies carry further due to having more energy and longer wavelengths. Think about standing outside a nightclub and hearing the kick and bass from outside and this will become more apparent
Late reflections are generally thought of as a much more diffused sound that blends together in a way that it feels like one unified sound as opposed to hundreds of distinct echoes.
Many producers will instinctively reach for the reverb decay time when trying to create a large space. This will help in some ways, but it’s actually much more logical to use the pre-delay and early reflections wisely before touching the late reflections. Because the early reflections coupled with pre-delay are the parts which define the dimensions of a room. Whilst Late reflections do play a part, they also have a lot to do with the shape and surfaces of a room.
The reason for this is because the early reflections coupled with pre-delay, are the parts which define the dimensions of a room. Whilst the late reflections do play a part, they also have a lot to do with other elements such as the shape and surfaces of a room.
There is no real life space that would have late reflections without early reflections. Therefore the early reflections are always going to be the driving factor for creating a sense of the dimensions of the room.
Reverb Pre-Delay In More Detail
The pre-delay can do a whole lot more than just define the dimensions of a given space, it also has a range of other uses which can be more easily understood when visualised.
- Helps to add clarity and intelligibility
- Keeps parts sounding up front, even in a large space
- Adds separation between the direct sound and start of the reverb
- Can be used to create a distinct slap-back type reverb/echo
- can be set to fit in time with the tempo of the track to enhance the groove
- timed pre-delays can help us to blend more reverb into the track without it being as noticeable
Reverb Pre-Delay Calculation Formula
For this tutorial, we will focus on syncing our reverb to tempo in order to help it blend into the track and work more naturally with the groove.
This can be achieved using this simple formula:
milliseconds per minute / Project Tempo = milliseconds per beat (quarter note)
This quarter note value can then be further sub divided until a suitable pre-delay time is achieved. Pre-delay values ranging anywhere from 5ms to 60ms are fairly standard. with shorter values being used for smaller spaces such as drum rooms and larger values being used for larger spaces.
There are 60’000 ms in a minute. So the only other part of the formula you require is your given project tempo.
Here is a breakdown of the formula in use for a project tempo of 120 Bpm.
- 60’000 (ms in a min) / project BPM
- 60’000/120 = ms per beat
This gives us 500 ms per beat (quarter note)
Obviously, this value is way too large unless we want to use the pre-delay creatively for adding rhythmic delays. Lets sub-divide by 4 to give us the pre-delay value for a 16th note.
- 500/4 = 125 ms
This is closer but we still need to tighter pre-delay settings.
- 1/64th = 31.25
- 1/128th = 15.5125
- 1/256th = 7.756
There is no need to be quite this precise when setting your reverb times. It is best practice to round your delay times up, as this will add a slight amount of groove to the delay time and push the early reflections back into the ‘pocket’ of the sound. Once you have set your value, always use your ears and nudge the pre-delay slightly forward or back to find that sweet spot where the pre-delay sits nicely with the original signal. This is what people mean when they refer to the ‘pocket’.
Alternative Methods Of Syncing Reverb Times
Having to get a calculator and figure out the formulas is quite a drawn out task. So an easier way of doing this is by using online pre-delay time calculators. Many of the online calculators will also give you values for triplet and dotted times as well.
Here is a link to an online reverb calculator, as well as plenty of other useful resources such as test tones.
Studio Slave Reverb Delay & Pre-delay Calculator
BPM Beat Division Calculator
How To Tempo Sync Your Reverb Pre-Delay Time
Once you have the beat divisions, setting the pre-delay to fit the tempo couldn’t be more simple.
- Load up your reverb
- Remove the late reflections entirely! this will make it much easier to set the pre-delay and early reflections
- Input the time value from the formula, remember larger pre-delays create larger spaces and more clarity, whereas smaller ones can be used for creating a distant, far away feel and also come in handy for smaller rooms and to glue mixes together.
- Nudge the pre-delay forward or back to find the sweet spot or an area which complements the groove
- Check it with your ears and make sure it definitely sounds right, don’t solely rely on values from the formula as each tracks groove is subjective
- bring the late reflections back in
How & Why You Should Tempo Sync Your Reverb Decay Time
Now that we have set our pre-delay, we can use the exact same principle on our reverb decay time as well. Setting this in time with our track is going to be extremely useful and is something that most producers do subconsciously anyway.
RT60
The RT60 is the amount of time (in seconds) it takes for the reverberant signal to fall below 60dBs. This is how the acoustics of a room are measured.
We can apply the same formula we used earlier to sync our decay time to the tempo. Usually, this will be a half beat, full beat or possibly even two beats.
Things to bear in mind is that we also need to take into account the reverb pre-delay time when setting our decay time.
So if we have a whole beat value of 500ms and our pre-delay is 20ms, we should set our decay time to 480 ms to compensate.
Just as we did in the first scenario, always re-adjust the time values using your ears. The reason for this is because the reverb tail may not reach RT60 till 500ms, but in the context of the track, we probably won’t hear the reverb decay after 300-400ms because of the subjective loudness of other parts of the track.
Key Points
• Reverb is made up of 4 main parts, direct sound, pre-delay, early reflections and late reflections
• Pre-delay and early reflections are the best indicators to define the size of any given space
• Formulas and online pre-delay calculators can be used to tempo sync our reverbs
• Tempo syncing can help a reverb to blend into a track and enhance its groove
• RT60 is the time it takes a reverb to fall below 60dB
• The decay time can also be set to fit the tempo of a track
• Always re-adjust timing values by ear
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