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Theory and Practice

FOH Magazine Theory and Practice - Passive and Active Crossovers

Crossing Over

We hear the term crossover all the time in pro audio, and crossovers play an extremely important role in our P.A. systems. A crossover (sometimes called a “crossover network” or “frequency dividing network”) is an audio circuit that divides the full frequency range into high- and low-frequency bands, and sometimes also mid-frequency bands.

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The piano is one instrument where either large or small-diaphragm mics can be used, depending on the desired sound. Photo courtesy Sennheiser

Mics: Does Size Really Matter?

Anyone reading FRONT of HOUSE is probably familiar with a variety of microphone designs using moving coil, ribbon or condenser capsules. I often joke that having a lot of mics is like having a lot of crayons: you don’t want the eight-pack, you want the super-variety pack with 152 colors and the sharpener built into the box. You never know when you’ll need that ever-so-subtle shade of color. If only mics were as inexpensive as crayons…

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Understanding Unity Gain: Waves H-Comp screenshot

Understanding Unity Gain

The concept of unity gain is deceptively simple: when the output level from a device is equal to the input to that device, you have achieved unity gain. It’s like a high level of Audio Zen, only better. When we say “device,” we can be referring to a hardware device or a plug-in — the concept applies equally in the analog and digital domains. The problem is that most “devices” are intended to mangle audio in some way or another, and that’s where simplicity goes out the window. Let’s look at a few examples.

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When you press that solo button, you’ll definitely be disconcerted to experience hearing the snare feed in your cans before it reaches the P.A. system.

Tick-Tock: What’s the Deal with Time Alignment?

A famous engineer on a Federation Starship once said “Captin, I canna’ change the laws of physics…”

Scotty may have been talking about the amount of time he needed to restart the warp engines, but if he was an audio engineer, he might have been referring to time alignment. Sound travels really s-l-o-w compared to the speed of light, the speed of electricity and certainly warp speed.

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FOH, 'Theory and Practice' column, Nov 2017

Exploring the Parallel Universe

Anyone who reads FRONT of HOUSE is probably familiar with the differences between serial processing and parallel processing. Serial processing is used when we want 100 percent of the signal to be processed and none of the “original” signal to be allowed into the mix. For example, when compressing a lead vocal, we most often insert the compressor on the lead vocal channel in an effort to control the dynamics of the lead vocal. This prevents the uncompressed lead vocal from reaching the mix.

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Fig. 1: For tom mics, a super- or hyper-cardioid pattern may result in less cymbal leakage — if the cymbal’s position coincides with one of the nulls of the pickup pattern.

Choose Your Weapons Wiseley

We all have favorite microphones that we prefer to use for particular applications. Some of the more popular suspects that engineers agree upon (!) include Shure SM57 on guitar cabinet, Shure SM58 for vocals, Sennheiser MD421 for bass cabinet, or AKG D112 for kick drum. The list could go on all day, and we could argue the pros and cons of the various tools we can’t live without.

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Knowledge, background and experience is what makes an engineer, not just buying some gear.

If I Had a Hammer…I Still Wouldn’t Be a Carpenter

“Peabody, set the WABAC machine for the early 1990s”… (cue Scorpions “Wind Of Change”)… Commercial recording studios are thriving. The record industry has not yet had to deal with Napster, and most people think that streaming refers either to a bodily function or a style of fly-fishing. Multitrack tape machines are still king, and analog is living happily alongside digital reel-to-reel tape.

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Too much of a good thing?

What Happened to Safety?

I’ve just returned from what can best be described as a hellacious three-week run of shows in the U.K. and Europe. Maybe I should modify that: I’ve just returned from a three-week run of hellacious travel. Truth be told, there were no bad shows, but there were a few incidents that I found disturbing.

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