The Onstage Sound Tipsheet (continued) |
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’ΔΆ Onstage mixers should be very clean since the house board will add its own noise. Line mixers, which don't include mic-level ins, are commonly used as onstage submixers. However, many models lack EQ as well as insert points for patching in external EQ (see sidebar "Recording Versus Sound Reinforcement Mixers"), making it difficult to compensate for problems such as whining synths or screeching guitars. Look for line mixers with at least some EQ and lots of effects sends. ’ΔΆ Powered mixers are cost-effective and convenient; for quick-and-dirty club or casual gigs, they're hard to beat. Listen carefully before you buy, though; unless the amp is well designed, mounting the high-current power amp supply next to low-level audio lines can create noise and hum problems. ’ΔΆ Most live-performance-oriented electronic musical instruments use unbalanced, 1/4-inch outputs, but if you have long signal runs, consider using balanced lines for instruments and effects. These allow for long cable runs (such as snakes to the house board) with minimal induced noise and signal loss. While expensive, this approach can work magic for hum problems. Driver boxes and adapters are available to match unbalanced instrument outputs to balanced lines. ’ΔΆ If you're submixing onstage and have a house mix, ground loops are likely because you and the house sound engineer are plugging in at different places. A mixer or a direct box with balanced outs, where you can lift ground, will give you ways to control the loops. ’ΔΆ A close to foolproof (but expensive) ground-loop solution is the one-to-one isolation transformer. This physically isolates two lines; disconnect each return until you find the source of the loop (the ground loop-associated problem will go away) and insert the transformer. Unfortunately, high-quality transformers (such as those made by Jensen Transformers, Inc., of North Hollywood, GA ) are $60 to $80 each. ’ΔΆ If you have to mix from the stage or have a less than professionally competent sound person, you'll usually want to mix the mains in mono; a stereo mix invites phase cancellation and balance problems, and most people in the room won't be in the "sweet spot" (the location where all instruments are properly balanced). However, if you want to use stereo, pan most vocals and instruments dead center (equal parts right and left), and sweep just those parts that are crucial to a particular effect. You'll get some of the impact of stereo without the hassles.
After getting your levels set, mark the pertinent knob levels and switch positions for all system elements, including submixer controls. (Writing on adhesive tape is one way to record these settings.) If the knobs are jostled, you'll be able to return to the previous settings. ’ΔΆ Older guitar processors sometimes have fairly low input impedances that can load down guitars or effects with high-impedance outputs. Should plugging into a unit cause a loss of level or high frequencies, insert a unity-gain buffer board before the low impedance input. Buffers are generally not available commercially, but building your own is a one-evening project. (See Electronic Projects for Musicians by Craig Anderton for a suitable schematic diagram.) |
’ΔΆ Open mics onstage can cause problems such as feedback, wind noise, and crosstalk. One solution (used by the Grateful Dead and others several years ago) is to put two mics on the same stand, over-and-under, just far enough apart that you can sing into one mic but not the other. Altering the polarity of one mic by 180 degrees, then summing its output with that of the other mic, produces differential cancellation of the ambient noise, since it feeds both mics more or less equally. However, the vocal, which appears predominantly in one mic, is not subject to the same degree of cancellation. ’ΔΆ On current tours, the Dead use dbx 904 gates, but the system is modified so that the gate's keying input (which provides external control for the gate rather than having it follow the internal threshold) responds to a trigger pad placed in front of the vocal mics. When the three guitarists step up to their mics to sing, as long as they step on the pads, the gates are open and the mics are live; otherwise, the mics are off. Sound engineer Dan Healy has two footswitches that allow him to control keyboard player Brent Mydland's mic and override lead guitarist Jerry Garcia's gate pad, since the latter tends to rock back and forth when he plays (see "The Dylan/Petty/Grateful Dead Tour" in the November 1986 issue of Mix magazine). ’ΔΆ Even a superbly tuned system is incomplete without protection for your speakers (and ears) from accidental bursts of sound. Limiters (which prevent signals from exceeding a particular threshold level) are usually the gadget of choice. The threshold level is critical; setting it too low creates a muffled and unnatural sound, but setting it too high reduces the amount of protection. Most limiters include visual indicators of how much limiting is taking place. ’ΔΆ Wireless headphone monitors with mics reduce feedback and allow you to roam around without leaving your monitor. If you try this, be sure you have a limiter on the monitors; by the time you can pull headphones off to escape a blast of sound, it may be too late.
’ΔΆ While 1/3-octave equalizers (typically having 27 to 31 bands) offer more flexible control than designs featuring ten or fifteen bands, it is nearly impossible to properly "tune" a room using a 1/3-octave EQ without the use of a spectrum analyzer. Unless you or your sound engineer is so equipped, the simpler 10- and 15-band EQs may give better results. ’ΔΆ Most active EQ circuits can boost signals by 12 dB or more at specific frequency ranges. Boost too much, and you'll send your power amp into clipping, creating distortion, or even blowing a speaker. Often the best way to avoid distortion is to cut out unwanted frequencies rather than boost wanted ones. (For more on EQ, see Craig |
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When it's time to mix signals together, you want the right mixer for the right job, and a recording console may not be the right choice for road use. Although this is a rough generalization, recording consoles usually offer more options than sound-reinforcement boards but are less roadworthy due to the extra electronics. A good live-performance board will not only be rugged but will use no more electronics than is needed to do the job. Multitrack recording often requires a board with as many independent master outputs as you have tape tracks, so most consoles Include a channel matrix for assigning channels to output buses. Recording consoles also have buses with either pre- or post-fader (often selectable) sends. Most sound-reinforcement applications involve a stereo or mono mix, requiring only two independent master outputs. Live situations may also require multiple monitor buses but the sends will be hard-wired in the pre-fader position so you can adjust the main outputs without changing the monitor levels. Equalization can be extremely important for live use if not overdone. Most low- to mid-priced sound-reinforcement boards include no more than three to four bands of EQ; look for at least one sweepable midrange control along with, if possible, variable bandwidth. For pop music, you can generally get away with fixed bands for highs and lows. Feedback and "honking" of instruments and speakers usually occur in the mids, so many quality sound-reinforcement boards provide 4-band EQ with two sweepable midrange bands. Better boards may include low-frequency rolloff filters to reduce wind noise or rumble. Also useful are insert points to add outboard EQ or limiting. (Many amplified acoustic instruments need a dedicated outboard EQ.) Sophisticated sound-reinforcement mixers and recording boards often have switchable |
insert points. A less expensive approach uses a 3-conductor jack in which the tip is the return (in case you want to inject a signal), the ring is send, and the sleeve is ground; the ring and tip are usually normalled to each other when no plug is inserted. Because you need to keep track of instrument levels under the sometimes chaotic conditions of live performance, metering must be highly visible, and there is a trend toward LED peak meters instead of VU meters. In outdoor applications, particularly in bright sunlight, LED displays are sometimes difficult to read, and in such cases, VU meters are preferable. Recently, some companies (notably Clair Brothers) have introduced boards with simultaneous peak and RMS (average) meters next to each fader. Snapshot automation is not usually found on sound-reinforcement boards, possibly because things change so much night to night. (There are also cost and reliability factors.) Hardware products (like Yamaha's DMP7 or Akai's MPX-820) and hardware/software computer add-ons (such as the Megamix, Twister, Mimix, et al.) can provide snapshot mixing of audio levels; if you're concerned only with levels of MIDI instruments, you can usually control MIDI volume in a number of ways. Still, few systems have live use in mind; possibly this unfortunate situation will be corrected soon (manufacturers, take note). Although recording mixers usually have everything sound-reinforcement mixers have and more, the high-end "live" boards have an amazing variety of features. Sometimes, as with Ramsa's top-of-the-line gear, they have superb grounding schemes that equal all but the best studio consoles. (Thanks to Larry "the 0" Oppenheimer for his considerable contributions.) |
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