Last year we wrote a blog post about Mix Glue, what it is, and how to achieve it with a buss compressor like Invigorate.
Buss compression is an ideal way to create Mix Glue, but there is another important method of adding glue and cohesion to your mix, and it’s something we’ve been studying this last year: Delay and Reverb for Mix Glue.
1. Delay and Reverb for Mix Glue?
To understand why echo and reverb are important for adding glue to your mix we need to return to the idea of “Systematic Perceptual Similarity.” As we discussed in the last post, the study of Auditory Scene Analysis suggests that our brains will detect two sounds as coming from different sources if there is a “Systematic Perceptual Difference” between them. That’s fancy talk for a difference between them which stays different for the length of the sound. We suggested that if we want different sounds to sound as though they’re coming from the same source we needed to create a “Systematic Perceptual Similarity” - a similarity between them which is constant for the length of the sound. Buss compression is a great way to do that, but there is another way!
2. What Does This Have to do With Echoes?
Another way to create a constant similarity between sounds is to place them in the same space. This happens automatically when we place instruments in the same room. They both excite the natural room resonances (called modes) and our ears pick up on that and our brain realizes that these instruments are in the same room. We call this room excitement Reverb and it’s a great way to put sound sources in the same place and add glue.
Practically, this is done by placing the reverb on a buss. This is a familiar tactic to most experienced producers and mix engineers, but in case this new to you, the trick is to place the reverb on an AUX RETURN track and set it 100% wet. Then for each track you wish to glue together you turn up the SEND knob to send the instrument into the room (to the reverb) and the fader on the AUX RETURN track is the amount of room sound you want in the mix.
3. Who You Calling Dense?
A problem you might run into is that reverb can be quite dense. When us DSP nerds talk about reverb we talk about two kinds of density; echo density and modal density, and there’s a tradeoff. The more echo density you the less you’ll hear individual echos in your reverb tail (sometimes called flutter echo), but the higher likelihood that you’ll hear specific resonances because you’ll have lower modal density. Similarly, if you have high modal density you won’t get ringing, but you’re more likely to hear distinct flutter echoes inside the reverb tail.
For a reverb to sound really lush and full you need a combination of high echo density and high modal density, which is possible to achieve, if not a bit tricky. However, these lush dense reverbs present their own hitch. THEY’RE VERY DENSE! This high echo density and high modal density actually takes up a lot of perceptual room in the mix, which can make a mix sound cluttered or busy.
4. Delay to the Rescue! (Reverbs Hate This One Weird Trick)
However, the tradeoff between echo density and modal density tradeoff does allow for a weird trick: a totally clean feedback delay can be viewed as a reverb with very low echo density and essentially infinite modal density - this is just another way of saying that it has distinct repeats and no resonances.
However, if we start with a clean echo and add a bit of reverb and filtering into the feedback loop we get a reverb with very high modal density (sounds great!) and low echo density. BUT(!) instead of nasty flutter echoes we’ve cheated and the echo times to rhythmically important parts of the music.
This creates a situation where we get the holy trinity:
Rhythmic support for the music
A lush reverb sound that doesn’t take up too much space
Systematic Perceptual Similarity resulting in MIX GLUE!
This is why the right delay really is my favorite reverb. It can put all the instruments in a space without taking up too much space. And this was one of our main goals with Recirculate: to create something sort of in between a delay and a reverb, something that would fulfill all these three requirements.
5. Glue vs Feature
There is something else to consider when thinking about mix glue and perceptual similarity. Mix glue is all about taking separate elements and creating a cohesive whole. We do this by running all the instruments through the same reverb or delay.
However, sometimes we want to feature a specific instrument, like a lead vocal. This can be done by placing that instrument in its own space by giving it its own, distinct, reverb or echo sound. Our brains will automatically interpret these two sounds as being different, and that will lift your vocal out of the mix and give it more presence. Practically, this can be done by using a second buss, or even just placing the delay or reverb on an insert. (The DRYFX knob on Recirculate is actually amazing at this.)
6. Glue for You, Too
Now that you know how to use reverb or (the right) delay to glue tracks together or make them stick out I hope you go give it a shot. If you’re interested in checking out a free demo of our not-quite-delay-not-quite-reverb Recirculate to do so, go click the DEMO button on this page.
Keep it together,
Dan