It’s kind of like a bank shot in pool when you deflect the ball off of the opposite edge of the table to drop it into the far side pocket. The fact that the projected sound has to travel to the boundaries of the room and bounce back to where the mike is positioned adds to the distance that the sound has to travel before it reaches the mike. This technique gives the sonic illusion of a slightly larger room.
Now let’s address a common issue: the room presents a harsh sonic environment. It’s your friend’s 10-foot-square cement basement for instance. When faced with this situation, you can do one of two things. You can either come up with some creative room treatments to warm up the reflective surfaces a bit, or try to minimize the sound of the room altogether by deadening the environment.
One way to warm up a cement room is to hang large sheets of plywood or lean them up closely against the walls. This changes the surface characteristics and could help improve the sound quality of the reflections. You could also try hanging a few blankets on sections of the walls to soften and absorb some of the harshness.
If the space is truly terrible, then you’re going to have to go to more extreme measures to make the room disappear altogether. A bad room is a bad room. In order to achieve a good drum sound, you have no choice but to kill all the reflections by using every possible measure available to you: hang packing blankets on the walls, use baffles to absorb sound and enclose the space, and mike the kit closely so you’ll pick up only direct sound without room reflections. So, you might ask, what then about ambience?
The first approach involves a fairly organic method for adding room sound. After you've killed the room reflections and recorded your kit close and tight, create a dry 2-track mix of the drums. Bring this mix to a space with good acoustics, such as the favored wood room with high ceilings or some other sonically pleasing environment. Send the drum mix through a quality speaker in the nice sounding room and record it by placing a mike out in the room to catch the reflections. Add that sound in with your dry mix and viola! It's almost like you recorded the session in that space! This is similar, says Borden, to re-amping a guitar.
The second approach involves a little digital smoke and mirrors to add ambient acoustics sparkle to a dryly recorded kit. You’ve heard of guitarists having the option of shaping their tone with amp modelers, and engineers having microphone modelers available to them. Well, it’s time to give the drummer some! If you have a computer-based recording/digital editing setup, you can use a plug in called a convolution reverb. A convolution reverb is essentially a "room modeler" that can help drummers especially to sweeten up their tone by adding in sampled room acoustics and reverberation.
What convolution reverbs offer are replications of acoustic spaces enhanced with algorithmic reverberation with controllable parameters. A convolution reverb works off of the impulse responses of a room, offering a natural sounding ambience by capturing the response, removing the transient, and adding the decay. It emulates various rooms, allowing you to create the illusion that your drums were recorded some place spiffy instead of, say, your cousin’s garage.
Running a signal through this processor will enhance the sound with the sampled acoustic response and allow you to control various settings in the reverberation. The result is that you have the realism of sampled acoustics and the controls to shape the sound according to your taste. It's more natural sounding than just sending your mix through a synthetic reverb.
There is a number of convolution reverb plug-ins on the market, from inexpensive versions to wallet whoppers with lots of bells and whistles. Generally, depending on the features offered, prices for plug-in packages range between $150 and $2000. Some examples include Wizoo, Altiverb, and the Waves IR-1 Convolution Reverb Series. Digital editing programs that include convolution reverbs include Nuendo, Sonar, and Sony’s Sound Forge among others.
The first idea is to use the room track(s) to facilitate a “live reverb” effect for just one or two elements of the drum kit, such as the snare or the toms. Insert a gate on the room mike track(s), and feed the signal from the close mike (on the snare, for instance) to the key input of the gate. This allows the close-mike signal to trigger the opening of the gate on the room mike, letting the room sound through when the snare is hit. Set the release time on the gate long enough to achieve a natural sounding decay. In this way, you get a natural reverb on just that one element for a tighter, more-focused overall sound if that’s what you’re after.
Speaking of focus, combining close-mikes with room mikes can sometimes result in a boomy-ness that could muddy up certain sounds of the drum kit (i.e., the bass drum) and you could lose articulation. In order to fix this problem, try using a high pass filter set at around 100Hz or so on the room mikes to clean up the kick. When setting the roll-off frequency on the filter, however, be sure to not cut so much that it obscures the body of the toms that got picked up by the room mikes.
If you work with Pro Tools, Digital Performer, Nuendo, or some other such program, utilizing the time alignment feature could help clear up definition issues with a drum mix or imbue the mix with a modern pop sound, offers Theakston. The depth of field provided by the room mikes adds distance to the drum sound, but may obscure certain elements of the drum kit under other instruments in the mix. Try moving the room mike track(s) to be in synch with the close mike track(s). Allow about a millisecond per foot, as sound travels at 1,130 feet per second. If the room mikes were eight feet from the drums, move the track eight milliseconds back to align with the close-mikes. This would result in a more instantaneous reverberation, culminating in a more processed sound using real acoustical characteristics to get there as opposed to algorithms in a processor.
This approach works best for straight-ahead, simple patterns by reinforcing the explosiveness of certain drum sounds, such as the snare or the toms. It may not, however, work quite as well for a kit being played with lots of cymbals and fancy tom work because of phase differentials between all the sound sources.
For instance, the idea of enhancing certain elements of the kit with natural reverb via triggered gates can be combined with the re-amping idea. By creating a dry mix of the kit that augments, say, the snare in particular, and sending that through the speaker to record in a nice space would serve to focus on that one element coming forward and being reinforced by the room. Or you may try running a mix of the drums through a speaker into the drum room while the drums are being recorded. Combining the amplified sound with the acoustic drums will give the recorded kit a super live sound. Remember that the absence of ambience is a sonic signature as well. Mix it up. Be creative, and have fun!