- Posted: 14/03/26
Total TDR (Time-Delay & Reverb) Unveiled!
Through 4 SPS articles we’ve covered recording studio acoustic design, D.A.W selection, EQ, and Compression. In the 5th installment of the SPS we’ll take on TDR which will be the last in our processing section of the series. We’ve discussed a lot about why equalization and compression are integral to achieving relatable mixes that are of professional quality. Another aspect often thought of as an “effect” really is a lot more essential to the sound of your records then you may initially think. Time-Delay and Reverb may be used to add extra “ear candy” to your record, but since at least the 1950’s, it has also been used in the same way as have compression or equalization, just to make recordings more realistic, aside from doing anything really interesting or groundbreaking. In this article we’ll focus, much like we did in the last article on compression, on a foundational “working knowledge”. Without discussing any particular reverbs or delays in depth, we’ll try to get a better grasp on how to use reverb and delay controls, as well as, impart a little more information on why we use them and how they affect our mix.
A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air- as defined by Lloyd, Llewelyn Southworth (1970). Music and Sound. Ayer Publishing. p. 169.
(Lexicon’s classic reverb in Plugin form)
I tend to think the majority of the time when a reverb effect is applied to a recording correctly we don’t notice it, or at least we shouldn’t. The majority of the time I add reverb to a recording electronically is when I am trying to make an instrument or vocal sound more natural or fit better within the mix of the arrangement. Of course, the digital reverb we apply today originates from a desire of recording engineers to recreate an effect that happens naturally. I’ve had the pleasure of recording in some pretty decent halls as a classical bassist aside from my more in depth study as a recording engineer and some of the magnificent orchestra halls are acoustically treated to be a very important part of the listener’s experience. Orchestral halls are designed to pleasingly reverberate direct sound from the stage back to the listener to create the elevated sense of ambience we’ve come to expect when attending a major concert. Recording engineers set out to replicate sounds like these in sound proof deadened studios, and so need digital reverb to create that second half of the sound we are accustomed to. One half is the direct sound from the sound source that we can get from the musician, and the other half from the room, which we can’t generally replicate in any reliable way without being in that exact room with those same musicians. With that dilemma set, this gave birth to digital reverb. There are of course many other types of reverb that aren’t specifically associated with recreating room sounds, but the task of recreating naturally occurring ambience from a range of different areas was born from this sort of need. Many of the reverbs we use today however, don’t necessarily attempt to create anything natural, i.e your analog plate reverb or many of the digital emulations.
When might we use reverb? Many of the studios that exist today tend to be more focused on recording a sound source in a deadened room for two main reasons, the first, it is incredibly easy to add digital reverb to any sound source in the D.A.W age, the second, it is far harder to take a “room sound” out of a recording then it is to put a recording “in a room”. If your lead vocalist is the lead character in a film and is screaming at the top of her lungs at the base of a canyon, there’s an app for that, lol…well not really, more like, there’s a plugin setting for that, but you get the picture. If your guitarist is in a Gun’s and Roses cover band and is attempting to sound like he is playing in an arena full of 20,000 screaming fans, well…there’s a reverb setting for that as well. So the many applications of reverb lead to the many variations of the tools we have at our disposal, from the physical plates and springs to the legacy of Lexicon PCM digital units and the convolution reverbs like Logic Pro’s Space Designer. The focus on the reverb parameters are where we will drill down next and try to get a better grasp on how to manipulate our sound.
Pre-Delay- This parameter is set to determine how much of your direct sound is heard before your reverb starts. This is set in ms and generally for anything that you want to be clearer and upfront you will want to use this parameter and set a healthy time frame. For instance, I’m usually setting at least 20ms pre-delay for vocal reverb.
Decay Time- Ever heard of RT60? This is the time it takes for your reverb to reach 60db below its initial level. This too is set in ms, and remember when trying to use this function to emulate rooms or halls etc. your RT60/decay time will be lower when in room with people or “stuff” in it. An example would be if you choose a hall reverb with a decay time of 1.2 seconds and then you decide you’d like to simulate that hall being crowded with people, you will want to shorten your RT60 because people will absorb the high end as well as hasten your decay time. This, of course, is the same for any setting. If you empty your bedroom your RT60 will increase, whether that is a noticeable increase is another thing. If you are in a very reverberant area your RT60 will be longer.
Density- The space you are in will directly relate to how dense your reflections propagate. If you are in your bathroom your reverb density is greater than in your absorber filled recording booth. If the room is made of highly reflecting surfaces your density will increase, i.e. maybe you are in a room with a hardwood floor perhaps. Manipulating this control will mimic the surfaces in your space.
Early Reflections- This parameter is often set apart from the main reverb. In addition to being set apart from the main reverb, it also sometimes has its own parameters for decay time and pre-delay. If you remember from our discussion on acoustics , early reflections are the reflections of the direct sound that are so quick (usually within 5ms) that they shape our idea of where the sound is coming from in addition to what type of environment it is in. Early reflections are heard as part of the original sound. So, in the digital reverb domain it is very important to shape our early reflections in accordance with how far our sound source is from the nearby walls or reflective surfaces. If your sound source is in a small reflective room early reflections will be 1) more plentiful, and 2) more dense, not to mention that on the actual reverb your RT60 time will be longer. One more thing on early reflections, even if your sound source is in a large room, if they are near a wall in that room, the early reflections will be faster and denser. This is the type of situation where it is imperative to have a reverb unit with the capability to separate early reflection control from the main reverb, because your RT60 may be short but your early reflections will be fast and dense.
Damping- Reverb inherently is more of a low passed effect. What does that mean? Well high frequencies don’t travel as far as low frequencies and higher frequencies are absorbed at a higher rate as well, so the natural character of a room leads longer reverberation having more low frequency content as opposed to high frequency content. If you are in an empty room you are more likely to have higher frequency content in your reverb for a longer period of time then if your room was full of people or furniture, because those things absorb the higher frequency content. It is important when dealing with your damping functions and EQ functions in your reverb to reflect this. If you are going for any kind of real world emulation of a certain space you should think about the aspects of your room and what inhabits it when manipulating your damping control. Just for an example, it’s not uncommon for your damping eq area to look similar to this:
(Courtesy of musicianself.com)
Just as an aside, I also tend to cut a little low end out of the reverb area as well especially if I am worried about things getting too muddy or if I have a lot of low frequency content in the arrangement at the time the reverb is active.
Output- This is the easy part of the reverb application. This is where you need to decide how much dry and wet signal you want and in what ratio. It’s almost always easier to setup your reverb as an aux send instead of as an insert so I’d start with that. When your reverb is set up as an aux send you can then set the output to 100% wet (meaning no dry signal) and use your fader of the main signal and of the reverb return to test out what amounts of reverb work best for you. One technique I often try works like this; I take my 100% wet reverb to unity gain and close my eyes (this helps me focus on my ears instead of my eyes i.e. the graphical interface) and pull the reverb down from unity until I get the sound I am looking for. Sometimes I think we can be too visually led by what our eyes tell us we need when we should focus on what our ears are telling us, and this technique works well for me to stay focused on how the reverb send works with the mix. If you do choose to have the reverb as an insert however, you should set the dry and wet parameters in the plugin or outboard gear. I’d focus on keeping your dry signal at 100% and then adjusting the wet output side to taste. One advantage of using the reverb send technique is the fact that you can send multiple units to one effect which, of course, saves processing power but also lends to a more uniform reverb sound if you are going for that “everything recorded in the same room” sort of feel.
One more thing I think is worth pointing out when it comes to reverb, How do we hear it?
When we talked earlier about Early Reflections I noted that Early Reflections are generally under 5ms. I also talked more about that in the first article in the SPS on acoustic design. Well, there are a couple other things I think that would be helpful to mention in this territory and would probably help you become more of a master at “knowing” your reverb unit. I put knowing in quotations for a reason. I think, as you study audio engineering your knowledge moves in stages: stage 1) knowing what tools to use for what, stage 2) knowing how to use said tools better and manipulating them to get your desired result, stage 3) knowing why said tools are used and what makes them effective so that you can dissect the instruments and used them in every way possible. These stages can definitely overlap and so that’s why I think this next tidbit of information may be useful to anyone in “stage 3”.
For me, everything concerning reverb before 2ms delay is heard as part of the initial sound. The sound starts to separate clearly at 5ms, but I do hear a difference a 2ms. You can try some listening trials in your own space to see when you can definitively tell there is another sound coming from another source. At 50ms the sound is heard as an “echo” as a completely different sound, much like your delays that you may hear in pop music. They would generally be 50ms or more. So, knowing these parameters 5ms and 50ms can help in deciding your pre-delay times as well as helping with the other topic we will cover next.
You are going to notice that Time-Delay (referred to henceforth as Delay) and reverb have a lot in common and so the delay section will be more of an abbreviated look. The reason why delay and reverb have so much in common is because reverb is actually a function of delay. The Early Reflections parameter in your reverb unit is just a section to manage your shortest delays in your sound field. Of course, the main functions of your reverb ambience are made up of delayed reflections from neighboring boundaries. For this reason you will notice that many times your reverb plugins will also have delay functionality.
One of my main points about delay was made in the paragraph right before this delay section, so definitely check that out. Once you know how you want to apply your delay, either as part of the original signal (meaning less than 50ms) or as a separately heard sound (50ms or greater) you now have a starting point of where to set your controls. Many digital delays or plugins have tempo sync, which I often employ to keep things in time with the other elements of the song. There are a few delay specific controls that we need to know about too, so let’s just run by those:
(Logic Pro’s Tape Delay Plug in)
Feedback- Try turning up this function and you’ll notice how the delays increase and actually propagate. The feedback function will increase/decrease the density of delays that propagate. Just imagine the loudspeaker in an auditorium sending additional delays of the direct source back to the direct source.
EQ section- Think about the delay you hear when you yell down a long empty hall, or the delay you might hear if you yelled at the Grand Canyon, and even the delay you hear on your favorite pop/rock or hip-hop record. The sound source loses high frequency content as it is reflected back to your ears. The EQ section of your delay unit should reflect this (if you are trying to replicate a natural sound). It is common to hear your delays diffuse in intensity and in frequency content as they decay so many of your delays will have a low passed sound to them. It’s quite popular in R&B and Pop music to even do a “telephone” EQ on the vocal delays as well. This is where High frequency and low frequency content are taken out.
Spread/Pan- Pretty self-explanatory if you’ve used these features in any other part of your audio chain. Many delay functions are stereo, so in this section of your delay device you can manipulate the width of the delay effect which inherently delays one channel of the delay from the other channel. (A lot of delay there, I know) You can also set panning effects which in many cases increase the perceived effect of delay. I often use delay plugins with short times to just thicken up a lead vocal much like a double tracking would, but with more consistency then humans can produce, and I will use panning features to increase the sense of stereo width.
Pre-Delay- *Refer back to the definition in the Reverb section*
Output- Much like reverb, delay is best used as an aux send effect. If used as an aux send you can turn the effect to 100% wet and set the faders to taste. If you do decide to use the delay as a channel insert you will want to adjust the dry and wet output percentages accordingly in the plugin or delay effects box.
We’ve taken the opportunity in this article to touch on the parameters that control our use of reverb and time-delay. There are many types of delay (Analog, digital, convolution) and many variations on reverb(halls, plates, springs, rooms) but, a grasp of each function will allow you to take a closer step to using each system to get the results you want. Remember how the human ear works when it comes to delay, and adjust your times accordingly. We know to be cognizant of pre-delay in both reverb and delay scenarios as well as our eq and decay times. Both functions we have illustrated are low passed functions in general only because of the way high and low frequencies dissipate. Taking all of these things into consideration along with taking time out from mixing to experiment, getting to know each unit or plugin, we should be better suited to understand and master every function of this processing tool.
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