Knowing Your Knobs: A Fundamental Guide to Analog Consoles

In Uncategorized by tfwm

If you have operated a mixing console for more than ten minutes, then someone has probably asked if you know what all the knobs do. Could you honestly say “yes”? If not, then let us take a quick tour of an analog mixing console.

In this article I will be combining the typical features found on many different consoles in order to make sure that all the primary functions are covered. Each manufacturer chooses to leave out or to include features to get their console into the price range they want. Including every possible feature would make the average console too massive and too expensive. Every knob, button, fader, and meter takes up space and adds weight. While the console we are about to explore does not actually exist, each of the features can be found on some console somewhere. Well, actually this console may exist somewhere— I once used a Paragon console that had everything on it except for a tap that dispensed Fanta.

A modular console has individual channel strips or a small group of channels that can be removed as a unit for repair or modified as desired. For instance, many brands have a jumper on the circuit board to configure the direct output signal to originate before it reaches the fader section of that channel, also known as a “pre-fade” send. Recording sends are most often configured for post–fade (signal originating after the fader section), but personal monitoring platforms require a pre–fade signal. Similarly, there might be a jumper for making the channel EQ section apply to the monitor sends, or there may be a configuration to add an insert point. Because analog consoles have actual components and not digital processing illustrated by pictures on a computer screen, one needs to be able to access these components when making configuration changes.

Understanding the back of each module is important. There will be an XLR microphone input connector and most often a 1/4 inch line input connector. On lower budget consoles, the line input will be unbalanced while on nicer desks, it will be a TRS (tip-ring-sleeve three conductor) balanced audio input.. Another connector found on the back is the channel insert point. An insert provides a connection to interrupt the signal flow to alter the signal in some way. Most common is to add a compressor or equalizer. Only the most inexpensive boards will not have insert points. Channel direct outputs were once provided only on desks intended for recording purposes. With the growing popularity of personal monitoring platforms (such as the Hear Back or AVIOM system), the direct output is now a serious feature found on many lower cost consoles.

Across the top of our console sits the meter bridge. Do not assume that LED’s are more accurate or higher tech than analog meters. In fact, the more expensive the console, the more likely the meters will be analog VU meters. On a full featured console, the main outputs and the mixes will have dedicated meters.

At first glance, you notice that every channel strip looks exactly the same. Whether your console has eight inputs or eighty, you only need to learn one channel strip to learn them all.

At the very top of the channel strip there are generally three buttons. First is the phantom power button sometimes labeled as +48V. Condenser microphones and active direct boxes need a DC voltage (provided by phantom power down the microphone line) in order for them to function properly. For everything else plugged into this channel including dynamic microphones and passive direct boxes, turn phantom power off.

Next will be a button with the Greek letter theta. For us non-Greeks (though we may be geeks), that is a letter O with a line through it. The button is called phase reverse. The phase reverse switch swaps pins two and three on the XLR connector. Sometimes a microphone will sound better if the phase is reversed (depending on how the microphone is designed) or it can partly make up for bad mic placement.

Our third button is the mic/line selector. This button may be labeled pad on some consoles. A true line selector switch bypasses the microphone preamplifier providing a pristine sound. However, a pad will reduce the incoming audio by 20dBv, or about 75% before the signal reaches the preamplifier. If one feeds a line level signal into a microphone preamplifier through the microphone input, the chance of distortion is quite high. If you have the gain turned all the way down and the signal still distorts, engage the pad. It is better to have the gain all the way down and make allowances with the fader than it is to engage the pad and have to bring the gain way up. This approach will result in a noisy signal. Even on very good consoles, you can hear a sonic difference with the pad inserted.

The first knob in the preamplifier section is the gain knob. The single most important concept to understand in audio is how to maintain proper gain structure. More important than EQ, more important than good monitors, perhaps even more important than fresh Krispy-Kreme doughnuts, gain structure sets the operational limits for the entire sound system.

Different manufacturers use different names for the gain knob, but it is always first in line. “Gain” and “Trim” are the two most common terms, but I’d like to place the word “Sensitivity” in your mind. If the knob is turned all the way down, the system may not be sensitive enough to pick up sound from the microphone, and any sound that is picked up will have excessive hiss. This is also known as a poor signal-to-noise ratio. If the sensitivity is too high, we will have distortion or clipping in the preamplifier section. If you have ever heard someone talk about “clipping the mic” which describes the crunching noise of distortion, it is most likely not the microphone’s fault. The gain is too high on the console at the preamplifier stage. Once you have distortion at the preamp, no amount of EQ will ever fix it. Gain sets the sonic quality limits for the entire system.

Right below the gain knob, there will be a button, or on nicer consoles, a knob labeled high pass filter. If it is a button, the filter “knee” frequency will be either 80Hz or 100Hz. A variable high pass can be anywhere from 20 to 400Hz. A high pass, a.k.a. low cut filter, is very useful for eliminating low end feedback, stage rumble, and HVAC noise and proximity effect from hand held microphones. When you use the high pass filter on vocals; it can make a world of difference.

Next is the EQ (or equalizer) section. Almost everyone is familiar with tone knobs, treble, mid range, and bass. EQ is just tone control. Some small consoles offer only high and low EQ. Most any console worth owning will have at least high, mid, and low filters. In those cases, the frequencies affected by the control of each filter are set by the manufacturer. For instance, many manufacturers choose 80Hz for the low EQ. All frequencies from 20 to 80Hz are either boosted or cut, depending on which way the knob is turned. If the knob is straight up, then there is neither cut nor boost and the filter is “flat.” On the high knob, the same thing applies, except the frequencies are from 10 kHz to 20 kHz. If all you have is one mid frequency knob, then the manufacturer has chosen that frequency for you. The filter frequencies can usually be found in the operator’s manual.

Many consoles offer another knob located right below the mid EQ. Not only do you get to cut or boost, you get to decide at what frequency. From 80Hz to 10 kHz is a long way, and you do not want to cut or boost that entire range, so the mid frequency selector lets you choose where to boost or cut the mids. On many consoles, there are two sweepable mid-frequency EQ filters. Upper line consoles have on/off switches for the entire EQ section that will take all the filters out of the signal path.

For those who care, the industry calls the two knob combo a mid-swept EQ. Preferred term is semi-parametric EQ. To be a fully parametric filter, there would have to be a Q (or bandwidth) control in addition to the cut-boost and frequency control knobs. There are consoles where there is a button to select one of two preset Q factors – wide or narrow. Q factor is how wide or how many frequencies are affected. To use an association—do you EQ with a rifle or a shotgun?

Next section down will be the aux sends. Auxes come in two flavors: pre-fade and post-fade. Some aux sends are flexible, and can be either pre or post fader with the push of a button. Pre-fade means the level of the output is independent of the fader and a signal is sent out the buss even though the fader may be fully off. On a post fade aux send, the output level is reduced by the number of decibels that the fader is below unity. We could discuss at length about the uses for pre versus post fade auxes, but for now, we’ll just say monitors should be pre fade auxes, and effects should be a post fade aux.

Sandwiched between the aux sends and the fader will be any number of tools, including pan, sub-group assignments, PFL, mute, mute groups, mute scene, and on some consoles, VCA assignments.

Pan is a film term for movement left to right. If we are mixing in stereo, pan allows placement of the channel in the stereo field and controls the amount of signal sent to the left and right channels. When mixing mono, the pan control is used in conjunction with the sub-group assignment switches to choose which sub-group, a.k.a. mix buss, will receive that channel.

PFL or pre fade listen, also called solo, is an important part of the mixing console. When the PFL button is pressed, two things happen. First, the selected channel is sent to the headphones so that the operator can listen to the input of that channel alone. Even if the channel is muted, one can still hear that channel in the headphones. Second, the selected channel is visually represented on the meter bridge. Experienced engineers rely on PFL to keep the signal below clipping, find mix elements, hear off-air instructions and more. PFL is a very valuable feature.

Mute is a button that everyone except the console manufacturers understand. On some consoles the channel lights up when it is on. One even used a red LED to indicate the channel was active and not muted. Some have a light to indicate the channel is muted. If it is not obvious on your console which way it works, check the manual.

Mute groups are a cool feature and powerful tool. You can program one button to control mutes on multiple channels. At my church, I have the praise team on a mute group so when they pick up their mics, I can turn everyone on at once. I have one for the praise team, one for the choir, one for band and one to black out everyone except the pastor’s headset. Mute scenes are pretty much the same thing, but under MIDI control. If you’re mixing a show or production, you can program mute scenes and just step through them one at a time. Just think, the keyboard player could run sound and lights, too.

And finally on our channel strip are the VCA assignments. VCA stands for Very Confusing Acronym. (Nah, not really.) A simplified explanation is that a Voltage Controlled Amplifier remotely controls the fader, even though the fader itself does not move. The reality is that when assigned to a VCA group, the VCA control places an attenuator in series with the channel fader. Think of them as a super sub-group. Still the standard in broadcast ministries, VCAs never get dirty or scratchy, never distort, maintain stereo image, and also control post-fade auxes. I have a favorite VCA console that I use in live mixing because each VCA also has a compressor/limiter built in.

VCAs are a very powerful mixing tool. For example, you can assign all the drum microphones to one VCA group and control the level and mute of all the assigned microphones with one VCA fader and mute button. It’s as if all the faders are ganged together and controlled by the one. Unlike subgroups that actually route audio signal, VCAs control level only and do not affect bussing assignments.

The master section of our console may be at the right end, or it may be located in the middle. Wherever the location, the master section will contain sub-group mix buss, masters, VCA masters, aux send masters, matrix masters, and main outputs. There may also be a talkback section and noise generator.

Matrix mixes are a lot like auxiliary mixes, except that an aux is fed by a channel signal and is controlled by the individual aux buss knob on that channel. Matrix mixes are usually fed by subgroup mixes and the stereo buss. If you want channel twelve up in aux four, you turn up the aux four knob on channel twelve. If you want sub-group six up in matrix one, you turn up the sub-group six knob on matrix one. Matrix mixes are not as precise as aux mixes, but are a lot faster to set up. For example, if you have the choir mixed onto one of the sub groups, you cannot turn up one voice, just the entire choir. I use matrix mixes for hallways and cry rooms as well as off-the-console recordings.

I’m often asked why aux masters are knobs while left, right, and mono masters are faders. The difference is space and money. Your console costs less and takes up less space if the manufacturer uses knobs. Several manufacturers do have aux and group reverse switches so that you can have aux masters on faders and the group masters on knobs. I use the reverse feature when a console is used for a monitor desk.

The master section is also where manufacturers stick little extras that make their product unique. One I know puts in a USB port for recording straight to computer. Another has an extra EQ for each sub-group. Of course, the ever-popular talk back mic input. Some consoles also have a signal generator either producing pink noise or a sine wave tone that can be assigned to any number of discrete console outputs.

The output section on the back of the board should not be ignored. Generally speaking, the more output options the better. Insert points for auxes are useful for EQs and compressors. Having several copies of the main output becomes important when you need to feed hard of hearing systems or send a feed to the fellowship hall TV or the like.

In a nutshell, from a nut case, this has been a quick tour of the knobs and connectors on an analog console. Analog boards were not called analog until digital came along—sort of like clocks. The fact of the matter is that the analog console is not going away any time soon. Analog is the foundation of audio. I recommend everyone at least be familiar with analog mixing before starting into the digital realm, but there are those who are ready for the next level. Digital consoles have some very nice features that analog consoles do not have (like complete mix recall), but analog consoles generally do the same thing for less money., Generally, digital consoles can pack more into a smaller frame. For instance, that Paragon console I mentioned at the beginning of this article—it weighed over five hundred pounds! Each channel strip was so long, in order for an operator to reach every channel, the console was curved, with the compressors almost straight up, barely within arm’s reach. But many people still prefer the control and sound quality of a good analog console.

Manufacturers are always looking for ways to enhance their product, but as far as I know, Dave Wagner has not convinced any manufacturer to install a PEZ dispenser beside the master faders, yet…

Much of this article is taken from the Hands Up! Hands On! Audio training workshops. See www.handsuphandson.com for details. Mark Nichols holds a BS in audio from Georgia State University. He is a senior design-build engineer, and teacher, with Cornerstone Media Group in Atlanta.