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This installment of Foundations of Audio explains one of the most essential ingredients in audio mixing, reverb—the time it takes for sound to bounce, echo, and decay during a live performance or recording. Reverb gives a natural richness to your recordings, which is possible to reproduce. Producer and audio engineer Alex U. Case covers the acoustic, mechanical, and digital means for creating reverb, and charts the parameters (room size, density, etc.) you'll need to know to take advantage of the original recording space and enhance it in post. He then shows how to simulate reverb digitally with effects, adding timbre, texture, and contrast, and improve the sound of your mixes with a sense of space and depth.
These techniques can be practiced with the free Get in the Mix sessions, currently available for Pro Tools and Logic Pro.
Room Tracks, where you record the room that you are recording in to its own separate track, deserve special mention. We've talked about so many signal processing strategies that are really built on reverb processors, patching in a reverb and manipulating it. Let's make sure we get the most out of every room tracking opportunity we can. We'll talk about some specific mix ideas, but allow me to offer some suggestions for the Tracking Phase. First, plan to experiment. Miking a room is difficult, it's a big space, and it can be hard to find the best sounding spots for microphones.
Second, while a one-track mono room has some usefulness, plan to set up stereo pairs instead. And if you're working in surround sound use four-, five-, and seven-mike techniques suitable to your surround sound format. You can always use a subset of what you track if desired. Third, all of the stereo and surround techniques you've learned about for recording an orchestra, a horn section or a drum kit, and I'm thinking MS, X-Y, spaced Omnis, ORTF, Decca trees and so on, all of those mike techniques are valid for room tracks.
Plan to use omni directional, cardioid and bi-directional pickup patterns. Condenser microphones, both large and small diaphragm, are the most common choice, but ribbons are often a great choice. Lastly, it's okay to go for quantity of tracks your first few times out if you have enough gear and enough inputs. That is set up several sets of microphones for the room, a closed pair, a distant pair, a high pair by the ceiling, a low pair by the floor et cetera. Audition them when you mix and hear what works.
Then through experience you'll find the room track techniques that help out your mixes the most. Now let's dive into a session and put some room tracks to use. Here's a project with good opportunities to manipulate room tracks. Have a listen to a bit of the chorus. (music playing) While the room tracks here labeled RoomStereo exists for the entire tune, I think it might be a good idea to just have them enter in the chorus, so I'll trim the start of the room track file accordingly.
There's a fill heading into chorus 1, let's grab part of it, let's just grab these two hits and check it. I want to make sure it sounds appropriate soloed as well. That is going to be close enough. We'll give it a short cross fade to silence, to minimize any clicks or unwanted artifacts. Over at the end, we'll just have a nice long cross fade.
(music playing) With the room tracks now confined to the chorus, let's listen to those room tracks and assess their sound. (music playing) The very first thing I check when I listen to room microphones is their balance left to right.
I adjust them in level and sometimes slide one track earlier or later until the room stays centered. In particular, I focus on the snare sound within the stereo room tracks and try to center it or get as close as I reasonably can. (music playing) Yeah, these are sounding perfectly balanced to me. Rooms can be a bit of a mess to sort out with the sound of the entire kit splashing all around. With practice, you'll get good at hearing through the chaos.
Satisfied with the left-right balance, the second thing I check is the tone of the room tracks. I'm most interested in their presence. I want good mid-range detail so that I get a wide live sense of each drum hit, particularly the snare. I have some concerns about these room tracks in their raw state. I'm liking the snare, but I'm worried about the level of kick and hi-hat in the tracks. (music playing) There's a lot of low kick leakage in these room tracks.
While it might sound thunderous and exciting at first, it's really hard to use the kick sound in a room track. A tight low end in your mix is usually best achieved by having the low frequencies come from a single track for each low- frequency instrument like kick and bass. When the kick hits your mix from multiple tracks, the kick track and the room tracks plus leakage from the snare, hat, toms, and overheads, the slow changing large wavelength low frequencies can collide with out-of-phase relationships among all of these views of the kick.
So most of the time, I mike up the room with a goal of getting minimal kick and maximal snare. In this case we'll have to filter out some lows. The hi-hat is more than loud enough in the overhead tracks closer to the kit, so I'm not looking for more of them in the room either. So I've inserted a four band EQ on the room tracks, and now I'm going to pull out the lows associated with a kick and the highs most associated with a hi-hat, hopefully without killing the sound of the snare.
Over in the Mix window it's easy to see that I've already pre-instantiated a few effects that we're about to walk through, including this Equalizer. I use this to pull out the lows and pull out the highs, focusing on the snare and trying to minimize the distraction of the kick and the hi-hat. (music playing) It's always a compromise.
To reduce the kick and hi-hat as much as we might wish, we end up losing too much snare tone. Obviously kicks don't just live at low frequencies and hi-hats up high, they're broadband sounds, they all overlap with each other on the frequency axis. But I think I found a decent place for the filters. We can now place these room tracks in the mix and add a bit of excitement and contrast. Remember, they enter in the chorus. (music playing) You adjust the level of the room tracks to taste. There's no right answer.
Try to suit the mood of the tune and create a sound you like. We could stop there, but I'm feeling greedy. Another common step we take with room tracks is to gate them so that they emphasize the snare hits and get out of the way in between. So I've inserted a gate with some messy results. (music playing) No amount of fidgeting with the parameters will get this gate to open naturally for each snare hit.
The kick and the hi-hat keep opening the gate. This is always a problem, and the convenient solution is to open the gate on the room tracks with the close mike on the snare. This is done using the key input on the gate. I'll feed the snare to the key of the gate by sending it to any available bus. I like Bus 3. My snare track is here labeled Snare-close, let's send it to Bus 3.
I'll raise it to unity gain to get the full snare, I'll make it a pre fader send so that later when I solo the room tracks which would mute the snare itself, it won't mute this send. So my gate will still open on the snare hits even when the snare track is muted from my mix. Over on the gate I need to set the key input to this Bus number 3 and set a SIDE-CHAIN to this key. Now the gate should have an easier time opening on snare hits because it isn't looking at the messy room track to know when the snare hits. Instead, it's looking at the closed mike snare track. Let's hear how we are doing.
(music playing) Well, it still won't open reliably, but we've got another gadget in our gated room sound toolkit. We can filter the Side-Chain signal to pull out some of the non-snare leakage that keeps misfiring our gate. Note we aren't EQ-ing the room tracks themselves just the Side-Chain signal that tells the gate when to open.
(music playing) That Side-Chain filter has further helped us stop the gate from misfiring on hi-hats and kick drums.
Let's check it out in the full mix. (music playing) To get the gate on room tracks to cooperate, it's pretty much always necessary to feed the close mike snare track into the Side-Chain and to filter that Side-Chain.
We can actually audition this Side-Chain if we want to hear what the gate hears when it's trying to decide when to open. (music playing) We've stripped away as much as we can to find the spike of energy on each snare-hit and use that to open the gate so that we get gated snare in the room tracks in every chorus.
(music playing) Still feeling greedy? Me too. The next step, compression, naturally. I've patched one up.
You can take this sound a lot of directions. (music playing) Let's see how that works as we transition into the solo.
(music playing) That could be a good path to follow if we want to make the effect more obvious.
Room sound, particularly compressed room sound always has a raw exciting quality. Not done? Well, you could still throw more signal processing at the gated snare sound. Here's a bit of guitar amp. (music playing) Now our chorus enters with a bit of caffeine.
(music playing) Room tracks are an important source of short natural reverberation that we often aggressively manipulate.
Here we just used EQ, a keyed filter gate, plus compression and distortion. Be sure not to overdo it. We have to serve the music. But you'll find some styles of music beg you to take it further, add delay, flanging, and some wah-wah, whatever you feel inspired to do.
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