Recording the Band—A Geek's Take

Mar 1, 2005 12:00 PM, By Eddie Ciletti

AUDIO FROM THE INSIDE OUT

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Last fall, I began teaching audio at a local technical college. Unlike typical sessions — where time is money — we have more opportunities to document audio experiments, some of which have already trickled into “Tech's Files,” with more to come.

Fig. 1: If "digital treble" is bugging you, then try a less-aggressive mic. The response of the Coles 4038 ribbon mic does not hype top end, and in fact, gently rolls off above 10 kHz. The "original" Sennheiser e609 is also worth checking out.

INVERSE AUDIO
I hope after reading this article that you will be inspired to record a rhythm section without processing, then burn an unprocessed rough mix to CD (with optional rip to MP3) and let me know how things play out. Understand that I am not “against” signal processing, I simply want to give sounds a chance to be heard — outside the studio, au natural.

When analog tape was the only option, it put its stamp on everything, like it or not. Digital has made the microphone choice infinitely more critical and that's the emphasis here — to re-evaluate your mic collection, your recording space and, uh, your ability to communicate with musicians and get them to listen as critically as you are. If something isn't working, then follow your intuition and fix it well before the mix — before the first note is captured.

My motivation is part reactive: When given projects to evaluate, I find that many of the same tricks have been applied, especially to drums, and I wonder why everyone is working so hard. When a track isn't working, we often solo that channel to evaluate and tweak it. If that track is a kick drum and it gets EQ'd and compressed, then it pretty much necessitates that the other drum tracks are similarly processed to compete. That's fine when it works, but it becomes a sonic sand trap when it doesn't. After checking out these tips, all I ask is that you try processing after the fact.

CREATING SONIC REAL ESTATE
While everyone else is boosting 80 Hz on their main kick drum mic, I pay close attention to proximity effect, with bass roll-off as my modus operandi. The more directional mics used on a session, the more potential muck (and less clarity) there will be in the bottom. I like to make room for the bass guitar and, at the opposite end of the spectrum, clear out the area that is often cluttered by electric guitar artifacts that can mask the more delicate localization (stereo imaging) information.

Many mic designs have been tweaked to overcome the inadequacies of age-old P.A. systems that lacked intelligibility and the “softness” of analog (tape and transformers). These characteristics were then “copied” to newer models. As a result, many dynamic mics have an upper-midrange presence peak, while condenser mics have a rising top end, neither of which are entirely necessary today, especially with the unforgiving nature of digital. This is one of the reasons for ribbon mics' current popularity.

The Coles 4038 ribbon mic (Fig. 1) is pretty much flat to 10 kHz, after which, it rolls off at 6 dB/octave. The Sennheiser e609 has a more extended, but unhyped response. The benefit of a mic like the Coles is that it filters out some guitar amp distortion. Of course, you can always use an equalizer to roll off excess treble and bass; sometimes, that's a psychologically difficult knob to turn. Again, the discipline of going flat forces you to seek out and try mics better-suited to the task at hand.

Fig 2: The proximity curves of the Electro-Voice N/D 868 kick drum mic detail how the mic's low-frequency output changes with distance.

DISTORTION
Tweed-era guitar amps tend to add warm harmonics to the guitar note fundamental, but as EQ options were piled on and power output increased, a more egregious type of power amp distortion resulted: harmonic distortion of harmonics. I refer to this as the broken glass/edgy sound that is fine for that Wednesday night beer-and-play, but not — in my opinion — fun in a recording environment. My first instinct is to turn down the master volume control. Class-A preamp distortion is richer and warmer than nasty Class-A/B power amp distortion.

My final guitar amp tip is wacky and easy: Turn the mic around. That's right, instead of pointing the mic at the speaker, do a 180 and point the mic in the opposite direction. This way, you'll get intimate bottom from the rear of the mic and whatever reflects back from the room toward the cabinet. It's less complicated than multiple microphones and has a similar effect.

DRUMS
There are many schemes to get more low end from a bass drum, but in my opinion, monitoring may be the dominant issue. Don't believe me? Here are two pictures to prove it. Figure 2 details the response of the Electro-Voice N/D 868 “kick” mic, with the proximity curves to the left proving, in theory, that low end should not be at all elusive.

Figure 3 is a composite of two images detailing the spectral response of a Sennheiser MD-421 and an AKG C-24 as they respond to the kick drum. In orange, the MD-421 is at the kick's shell (single head), and in green, the AKG C-24 is behind the drummer. The MD-421 concurs with the Electro-Voice N/D 868's proximity curves and, even with the bass roll-off switch set mid-position, there is ample bottom. So, before twisting EQ, take advantage of this simple “power tool”: the spectrum analyzer, perhaps the handiest workstation plug-in ever.

POLAR BARE
Placing multiple mics on any instrument requires that you pay close attention to polarity (not synonymous with phase!); otherwise, the bottom you are searching for will cancel out. Adding a distant mic(s) — assuming the delayed low-frequency waveform is in phase — also tends to make the kick seem more resonant, but at different frequencies than simply compressing the close mic (frequencies that are less obtrusive to the bass guitar, for example).

Fig 3: Two microphones responding to kick: One is close (Sennheiser MDF-421), and one is no more than five feet away (AKG C-24)

The MD-421 captured substantial energy between 62 Hz and 125 Hz, about 10 dB higher than the beater bump around 3 kHz. Meanwhile, the C-24 reveals a “bump” between 125 Hz and 250 Hz, essentially picking up where the MD-421 leaves off. The 421/C-24 combo produced a wide-band bottom that translated well on small and large monitors. Combined with the room mics, it was huge. For more info, follow the “5.1 drum” link from my homepage, www.tangible-technology.com.

OMNIVORE
For rock, I'm not a fan of two-headed kick drums, with or without the hole. (The hole often resonates and I'd rather not sacrifice an otherwise good sound with surgical EQ.) However, my solution is to place a large-diaphragm omni (in this case, an AKG 414) in between the rack toms on the beater side. This solves my proximity issue — eliminating the low-frequency guesswork — and delivers a cool beater sound along with a remarkably well-balanced “mix” of the kit.

Another way to get “big bottom” out of a drum kit is to find a spot in the room that supports the low end and put an omni mic there. (Directional mics can have odd-sounding off-axis response, while omni mics capture everything.) While the AKG C-24 placement is not quite what I mean in this instance, its stereo image is an obvious plus and approaches the coverage of an omni.

WHERE'S THE BEEF?
During the session that generated most of this information, all of the students were happy with the kick when mixed in with the other mics. However, when soloed, the MD-421 on kick sounded thin. Thanks to the Waves PAZ spectrum analyzer plug-in for Pro Tools, I was able to prove that the energy was there and that we simply weren't hearing it.

Low frequencies are elusive for three reasons: Our hearing is bass-shy, our monitors typically do not reproduce the full bandwidth and many control room environments often have serious acoustics-related problems in that region. If you don't believe me, then sweep a sine wave from 200 Hz down to 40 Hz and see how elusive bass can be. Then, pick a single bass tone and listen as you walk around the room. It will freak you out!

In this example, the Genelec 1031A monitors were freestanding, so they are less “wooly” than when placed on a shelf or meter bridge. One of these “boundaries” would have increased the bass response by roughly 3 dB (add 3 dB for each additional boundary), the very reason why many self-powered monitors provide compensation via rear panel bass roll-off and tilt adjustments. (Genelec's optimization guide is online, in case you've misplaced yours.) I actually prefer the extra bottom because my monitoring levels are lower than typical.

The road to sonic bliss is filled with obstacles. I hope you find my tips useful as you leap over them, rather than get detoured on the road to nowhere.


Eddie would like to thank Colt Leeb and Matthew Koehne at www.iprschool.com for providing the screen captures, and James Edlund at Electro-Voice for the custom proximity curves.






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