Choosing a Mixer by Ben Stowe, CTS

November 20, 2008 by Ben Stowe, CTS

When choosing a mixer for your system there are two critical factors you should consider. The first is the feature set. If it doesn’t do what it needs to, it isn’t a good fit. Likewise, if it is overloaded with unnecessary features, you have likely paid more and are carrying more than was prudent. The second factor is the quality of the board. The mixer may have the single greatest impact on the quality of your sound, and it has many moving parts that can become troublesome quickly if they are of poor quality.
There are a variety of distinctly different applications mixers are used in; live sound, broadcast, DJ, karaoke, recording and more. This article will briefly discuss live sound, karaoke and DJ applications. Even within those categories there are several distinct uses, a scratch DJ may have different needs than a wedding DJ. They may want kill switches, onboard effects and perhaps an optical crossfader to allow for rapid, fluid movement over many cycles.

DJ Mixer Essentials
Individual users will likely place different emphasis on different features, but the following are some important features that I feel are fairly universal for DJs and others: size and weight, input channels, balanced outputs, gain trim, and PFL level indicators. Size and weight really go without saying. We have to carry our gear from gig to gig. Input channels will dictate how much we can connect to the board. Some will need more channels than others, and of different types. Inputs can be mic, line, phono, S/PDIF (digital) and more. Balanced outputs are particularly important given the greater use of powered speakers. For sending the signal at line level over long distances, like those required to reach powered speakers, they have advantages. Lower current in the signal means lower loss, but longer distances carrying a low-level signal create more opportunities for interference and noise. A balanced connection helps preserve the quality of the signal.
Proper gain structure is fundamental for good sound. An input gain trim (not to be confused with the channel slider), paired with a PFL (Pre-Fader Listening) level indicator is extremely valuable in creating even input gains and avoiding distorted audio.

Sound Reinforcement Options
In live sound, there is a far greater range of options, but most units draw from the same roots. Top considerations are frame size, low cut, EQ strip, Aux outputs, phantom power, fader size, and mute groups. The frame size simply tells us how big the board is. Check how many mono channels (typically a mic or instrument input) and how many stereo inputs (typically for stereo devices, such as CD players) the board offers. Often a stereo channel is counted as two. I find this practice to be somewhat deceptive, but nearly every manufacturer does it. A 12-channel board may have 8 mono inputs and 2 stereo inputs.
A low cut is a button assigned to a frequency beneath which the sound is reduced or eliminated. For example, a 100Hz low cut will eliminate 100Hz and lower. This is very useful for vocal channels. It quickly eliminates handling noise and potential feedback for a frequency that will likely not be produced by the vocalist anyway. The EQ strip can offer a variety of features. For me it’s important to have sweepable mids. This means that I can not only determine the attenuation for that frequency, but also the frequency itself. My favorite consoles have two sweepable mids, a low-mid and a high-mid. This is very useful in fine-tuning an input right on my channel strip.
Auxiliary outputs are just that, additional outputs that can be individually mixed from the available channels for monitors, recording, and more. Having lots of auxes allows me to create lots of other mixes so that different performers can have different monitor mixes, all without affecting the main mix.
Phantom power is voltage that is transmitted through the microphone cable to a device connected to it. This allows those devices (condenser mics, direct insert boxes, etc.) to be powered by the console rather than a battery or external power supply. Small consoles typically have a global phantom power switch, meaning that every channel gets it or doesn’t. Larger and better consoles have groups of phantom power channels, or individually selectable phantom power channels. This allows us to send the power only down the channels we want to, and not the ones we don’t.
Fader size simply dictates how much real estate we have to move that fader up and down. The larger the fader, the more precise our adjustments can be. Sub-groups and mute groups are very useful in managing large mixes. They allow us to assign several channels to effects easily, or to make wholesale adjustments in a particular group of channels. Drums, for example, can be grouped, and once adjusted proportionately to themselves (snare, toms, kick, overheads, etc.), can then be raised and lowered all at once. Mute groups operate in much the same way. All vocal mics can be placed into a single mute group, for example, so that during a break all stage mics can be muted with a single button, rather than locating several buttons.

A Sound Decision
The common denominator between all these categories is quality. Your mixing board is one of the most crucial pieces of gear in the system. It is the part that you, the operator, interfaces with directly the most, and it is instrumental in the overall production of your show. A noisy board can compromise all great loudspeakers, amplifiers, media playback and microphones. One area that is very critical, particularly when working with vocals, is the mic preamp. This circuit takes the very low electrical signal produced by a microphone and preamplifies it before inserting it into the mix. It seems painfully self-explanatory, but bad preamps can lead to bad sounding vocals. Another critical area, particularly in live sound, is the EQ section of the channel strip. Many EQs can color the sound in unintended and undesirable ways, whereas some EQs have a particular sound that is sought after. You’ll often hear tour sound techs talk about the “British EQ,” for example. Lastly, and certainly not least, are the moving parts. These are the knobs, faders, sliders, buttons, etc. Poor quality here can lead to early failures, bad sound, and great frustrations.
At my gear supply company we offer consoles from less than $100 to greater than $400,000. I urge you to carefully weigh the features and pursue quality construction in your choice. Certainly we must be practical in what we spend, but the mixer is a poor place to be pennywise and pound-foolish.

Ben Stowe, CTS Ben Stowe, CTS (18 Posts)

Ben’s love of electronics and technology led to years of schooling in Electricity, Electronics, Robotics and Lasers. Ben supported himself through school by building and selling strobe lights and other electronic devices. He built his first DJ show largely from scratch and scrap, often repairing broken items others had thrown away because he could not afford to buy new equipment. He holds a Minnesota electrical license, and his AV installs have been featured in almost every major industry trade magazine. His relentless passion for education has led to a number of other certifications and accreditations, including the most widely recognized one in the AV industry, the InfoComm CTS. His love for education inspired him to begin the ProAcademy educational sessions, focused on increasing understanding of AV technologies within the industry. Ben has been involved in a number of technical writings, lectures, presentations, as well as research and development assistance with a number of manufacturers for products, industry wide. He is also a regular contributing author to industry magazines in the United States and Europe. Ben’s presentations have been featured across the world both as a part of industry leading trade shows, and as a presenter for various groups and functions. Some of these events include BPM in the United Kingdom, Mobile Beat, the ADJA National Convention, Wedding MBA, and a national tour as a headlining presenter for an industry magazine. The United States Armed Forces branches have also called upon Ben to provide engineering and training assistance. His highly informational, slightly nerdy and always funny presentation style have made him a favorite at events, while his sincere desire to help people with their application of technology have made him a favorite with them after the event. Ben serves the industry as the President of NLFX Professional, an industry leading supplier of sound, lighting and video systems, a role he has maintained since founding the company in 1993.

Filed Under: 2009, Sound Engineering for Mobile DJs