The role of Technical Director requires a fairly even focus across at least four production disciplines: Audio, Video, Lighting, and Staging. In this piece, we'll focus on Audio, and how to best approach the use of two specific audio equipment components: Equalizers and Compressors. At this point, it's fair to mention that the principles we're about to discuss exist in both analog and digital environments, to where I will cover both as much as possible in the available space.
A competent audio technician or engineer must have a firm understanding of how Equalization and Compression affect the audio signal and how to manipulate both.
Equalization
Why EQ?: There are a few reasons for equalizing, boosting or cutting, specific frequencies of the audio signal. For example, the FOH (Front of House) Engineer needs to control equalization for aesthetic reasons, perhaps to reduce the harshness of the sound that the congregation is hearing. The Monitor Engineer might need to control "feedback" (the return of part of an audio signal from an amplifier, back into the microphone the sound originated from thereby causing an audio loop) by reducing the amount of the offending frequency.
The FOH Engineer may also need to control feedback in the house, but it is often the case that it can be controlled by simply attenuating the signal. The Broadcast Engineer, or Recording Engineer, doesn't have to worry about feedback, because they are mixing in a controlled environment where, acoustically speaking, feedback isn't possible.
There are four frequency bands that need to be controlled in "the house" (worship environment or any other venue) or on stage:
High Frequencies: 6kHz-20kHz
Mid-High Frequencies: 2-6kHz
Low-Mid Frequencies: 250Hz-2kHz
Low Frequencies: 60-250Hz
Sub Bass Frequencies: 16-60Hz
If the FOH engineer is mixing monitors on the FOH desk, he or she would be responsible for controlling equalization in both the house and on stage. For this reason, the best practice is to have an engineer for both monitors and house, respectively. All of the frequencies above are represented on a Graphic Equalizer, typically the last piece of equipment in the signal chain before hitting the amplifiers, or the DSP in front of the amplifiers.
They are also represented on the Parametric Equalizer, typically found on every input channel of an audio console. Parametric Equalizers allow for selecting the exact frequency needed to attenuate without broadly affecting frequencies on either side of the target. The precise frequency is selected, in each band, then boosting or cutting is applied.
The ability to immediately identify a frequency is extremely important to knowing what frequency to either boost or cut. And when employing the "less is more" rule find frequencies on either side of a frequency you want to boost, and try cutting those frequencies instead.
There are several electronic means of detecting frequencies using either a computer or a handheld mobile device. For computer users, one of the most widely used software measurement tools is Rational Acoustics' Smaart. For the iPhone and iPad, there are FaberAcousticals' Signal Scope, and AudioTools Smaart® Tools. There are other similar tools the audio engineer can use to measure frequency response, but these are widely recognized and respected as industry standards.
Once an offending frequency has been identified, either because of feedback or because of harsh tones in the listening environment, the operator can then easily attenuate that frequency at either the individual channel strip of the console or the system Graphic Equalizer. Identifying feedback is easy, when you hear it, you'll know it's happening. Remember nothing beats a great set of ears and knowledge of frequencies!
Understanding how the ear responds to frequencies is important to contour the sound to achieve musical clarity and speech intelligibility:
High Frequencies (6kHz-20kHz): Very susceptible to feedback, delivering a bright sound, but not enough is dull. Such frequencies deliver sibilance in speech and some instruments.
Mid-High Frequencies (2kHz-6kHz): Snare attack between 4k-5kHz, vocal intelligibility occurs.
Low-Mid Frequencies (250Hz-2kHz): Reduce 250-400 Hz to thin out a muddy mix, and reduce 500 Hz-1kHz to fix the honking horn sound, reduce 1k-2kHz to fix a thin mix.
Low Frequencies (60Hz-250Hz): Provides the warmth and "fatness" to a mix, conversely, not enough delivers a thin sound, but too much is "boomy."
Sub Bass Frequencies (16Hz-60kHz): Delivers power and thump to your chest, but too much is also "boomy."
Compression
Why Compress? Compression is needed to control the dynamic range of individual audio signals, as well as across the mixbus in live, studio, and broadcast applications. The use of a Compressor is not as complicated as it seems. There are a few distinct sections of the Compressor that should be understood to set the Compressor for optimal use.
The Threshold tells the Compressor when to activate, although the exact moment the Compressor begins to reduce gain is called the Knee. The setting of a Hard Knee means that the compression will take place suddenly and is more noticeable than a Soft Knee. A Soft Knee setting delivers a smoother transition and is a less obtrusive change at the moment of attenuation. Setting the Threshold requires an understanding of how much level on the incoming signal you want - to activate the Compressor. Since the desire is to control high levels of audio, more often than not, you don't want to set the Compressor so that it activates at a whisper or a very low level of audio.
The Ratio tells the Compressor how much to attenuate (e.g., 2:1, 3:1, 5:1, 10:1). This means that if the Compressor is set to 2:1, for every 2db of sound over the threshold, 1db of output is released.
The Attack defines the time it takes the Compressor to start compressing after the Threshold has been reached. Let's break down that last point first and apply it to the crack of the snare drum and how it might be controlled. If the attack time is set to 1 millisecond (being fastest, while 100ms is slowest), the "snap" of the snare that is most impactful, might be missed.
Setting a slower attack time will compress the "meat" of the signal, controlling the overall sound of the instrument, while preserving the impact of it. The Release sets the time it takes the Compressor to return the audio signal back to normal after the audio signal drops below the Threshold.
All of the above applies whether using a digital or analog audio console. The only difference will be how you access the Equalizer and Compressor, using analog outboard gear, or utilizing a digital master channel to apply EQ and Compression. Learning and understanding frequencies will help keep feedback under control, along with overall gain attenuation, bringing the best out of musical instruments and vocals.
Correctly applying compression across a group bus, or directly to a vocal or instrument channel, will ensure a controlled and tighter mix. And correctly using EQ and Compression overall, helps achieve the signature sound of the Music Ministry, thereby fulfilling the role of the Audio Engineer on the Technical Team.