To some, reverb doesn't seem like that exciting of an effect. It's a very old effect. But to be honest: all effects are old. We really don't have that many unique processes to manipulate audio. With rare exceptions, ingenuity surfaces as plugin developers combine old effects in ways we haven't combined them before. But we're still left with the same old tools, just with new controls and new use-case scenarios.
So yes, reverb is an old tool. But if you're not familiar with it or don't turn to it often, it may be worth giving it another look. There are far more interesting presets than "Cathedral". And I've had friends tell me, "Yeah, the song's okay, but your vocals sound so raw..." after showing them a draft I'm working on just because I didn't start using reverb that early in the song. Reverb can be a core component in a parallel drum mix, and is often a key ingredient in powerful synth leads sounding big. And though my mixes often are on the dryer side compared to many, all of them use reverb in at least several of the ways below.
Where to Start
I don't intend to make my readers feel stuck if they don't have many reverbs to choose from. A bad sounding reverb plugin can be made to sound much better through careful mixing and integration, which we'll cover below. But it makes sense to start with the best reverb you have. Personally, I'm a fan of "Room" and "VintageVerb" by Valhalla DSP. They sound very clean and natural and open to me. I've also heard good things from impulse/response style reverbs. And plates can sound quite pleasing too, although that often is a preset style more than a specific plugin.
The only reverb that's on my shopping list currently is "Adaptiverb" by Zynaptiq. I haven't used it first hand. But I'm really intrigued by the approach of modeling the frequency spectrum around the spectrum of the sound passing through it. And its ability to drop out notes from the verb as the signal notes or chords change seems super usable. But it's expensive at $250, and as I said, I haven't personally used it yet. I'm vigilantly waiting for it to go on sale.
If you're not in the market for a new reverb, assess what you have. Play a simple sound through a reverb and listen to how real it sounds, how spacious it sounds. You kind of want it to have that dark, smooth cathedral-like sound; not that zingy, applause-like slapping of sounds. Listen for creaminess and convincingly delivering the sound of a larger room. To my ears, this makes a good reverb. And if you have two reverb plugins or twelve to choose from, I recommend testing all to identify your best (or best 20%, if you have many) and sticking with what you've found.
Proper Signal Routing
I know, it's so easy to put a reverb as an insert directly on the audio or instrument channel you want to affect. Particularly if you only want it to affect one channel. But it's critical to put the reverb on a send or a bus if you want to maintain the clarity of the sound through the reverb. When you slap the reverb directly on the track, the initial instrument and all its transients get buried and lost in the mix as you turn the wet/dry up enough to actually hear the reverb.
Let me use a real-world example to explain. What happens when a singer without amplification steps back in a large room while singing? The room gain of her voice increases relative to the "dry signal" of being close to her, but you still hear all the clarity of her voice if she's in direct line-of-sight. This is what you want to achieve when you set up your reverb.
How do you do this? Put the reverb plugin on a bus, not directly on an audio or instrument channel. And then create a send for the track or tracks you want to feed into the reverb. Set your reverb plugin to 100% wet. Control the overall volume of the reverb by moving the fader for your new reverb bus. And if you have multiple sounds feeding to it, you can adjust their balance in the reverb by adjusting the send level from each track. It doesn't just sound better, it's more CPU efficient to feed multiple tracks to the same reverb bus. And it also allows you to adjust how much reverb you want in a mix without altering the perceived volume of the dry signal.
Like everything that's an art, there are exceptions. A few that come to mind for me: I might want reverb to be integrated into a guitar sound before further processing, or I might want to chop up the reverb on a synth with pumping or volume shaping down the line, or I might want to process the instrument and reverb of a particular sound together. In these cases, it makes sense to put the reverb directly on the track being affected, or perhaps earlier in the chain, inside of a guitar multi-effects plugin or within the synth itself. I do this maybe one time in ten; the other nine times sending audio from a track to a dedicated reverb bus.
Using Reverb for Glue
Reverb can be a powerful tool to get instruments to sound more cohesive together. There are two ways to approach this:
The first is to send a group of instruments, perhaps all drums or all guitars, through reverb together. This is especially useful for blending with parellel processing, when you may want to create a separate bus for more extreme processing that's kept lower in the mix alongside the clean bus. For example, I may send all drums to the drum bus, which outputs to the master fader. The drum bus might have EQ and compression and other subtle processing on it. But that drum bus could also send to a drum vibe bus which outputs to the master fader. And that drum vibe bus might start with reverb, then get slammed by aggressive compression, then have distortion thrown on top, then heavy saturation, then low-fi processing. The drum vibe bus likely belongs much lower in the mix, but it can provide character and interest alongside the clean drum bus.
The second way to use reverb for glue is when you want the entire song to feel like the instruments were performed together, all in the same space. It works really well to create a reverb bus or two for all instruments to share. All instruments feed to it, though some more than others depending on the sound you're looking for and how you want to achieve depth in the mix. Another way to do this is to set up two identical reverb buses with identical settings for the room sound you want to achieve. But pan one reverb bus left and the other right. Instruments that are on the left get panned to the opposite, right reverb. And instruments on the right get panned to the opposite, left reverb. This is a useful trick to keep reverb volume lower in the mix while still having it be audible, and it's super useful for providing space and belonging to instruments, as if they really were recorded in a room together.
Different Styles of Reverb
It's definitely okay to blend different reverb sounds together. For example, I very often create two reverb buses right away for my vocals, though I may send other instruments to them later. One is a bit shorter, perhaps 1.5-2 seconds, adjust length to taste. And this shorter reverb receives a higher send volume to sound louder. And the second reverb is longer, perhaps 5-6 seconds, adjust length to taste. This longer reverb receives a lower send volume to sit quieter in the mix. The result is a nice blend of long and short reverb that tends to sound very natural and real to my ears. I'm not sure why I like it so much. Maybe because it sounds like you're just in front of a stage, and you hear the shorter, louder reverb bouncing off the back of the stage; and the longer, quieter reverb bouncing off the rest of the concert hall. Try mixing your own reverbs and see what works for you.
Reverb can also change based on the song section. It sounds good for lower, shorter syllables in verses to be sent to a shorter reverb. And the longer, higher, more legato and anthemic lines of a chorus can ring out with longer, louder reverb. You can do this with automation, but it may be easier to just put the lead vocals for the verses on one track routed to one reverb, and the lead vocals for the choruses on another track routed to a different reverb.
Reverb can also add a certain presence when it's super short. It's been a long time since I worked with mixing rap, and even longer since I worked with radio voice, but if you're aiming for something spoken that needs a little presence and power, try adding a super short reverb, perhaps with the decay time around 0.2 seconds. Adjust to taste. It can add a certain command and sparkle that's perfect for some situations.
I discovered that I really like dark sounding reverbs. I very commonly put an EQ on my reverb bus and roll off both the lows and the highs. Too much highs in the reverb and it sounds cheesy and fake. Too much lows and it gets muddy and masks the instruments you want to be audible. To be honest, I felt a little guilty shaping the reverb like this, figuring that purity was the ultimate goal and I was abandoning purity. But purity is a funny concept when mixing audio. Maybe a guitar layer needs to sound tinny and lean instead of rich and full, because the voice will add the richness and the bass will add the fullness; and there just isn't room for a super full sounding guitar in the mix. Don't feel you need to honor each track by making it sound its purest and biggest and fullest - instead, honor the entire mix by helping each instrument or layer sit where it needs to sit for the benefit of the entire mix.
Regarding filtering reverb, I felt less guilty as I learned that a number of famous producers and engineers also like their reverbs sounding very mid-rangy. See if it's a style you enjoy too.
But reverb can be made significantly dirtier still. For example, a few famous producers like to detune vocal reverbs just a little, to set off the original from the reverb and to make it sound darker and cloudier. I've begun using this on my mixes, and I have to admit, I like it.
Another way to make reverb dirty is to side-chain it to the metronome, or the kick drum, or just about anything else. Get the reverb to move and dance with the song.
Yet another way to make reverb dirty is to throw a distortion plugin on it, or add heavy saturation, or vintage simulation, bit-crushers, vinyl crackle, tape hiss, etc. Noise can add so much character, though I find I like adding noise that follows the original signal instead of noise that's purely random or purely constant. Blending is important. But adding dirt just wins in my opinion, when you get the balance right.
I don't expect that all of these tricks and techniques are new to you. But, hopefully I covered a method of using reverb that inspires you to produce more. And if you have a killer technique I didn't mention, I'd love it if you'd share it below so I can try it too. We're all in this together.