Analog Mixing Consoles Part 1

 

You may have used a basic mixing console when you were in a weekend band years ago, which is why you’ve suddenly been volunteered to run sound for a worship service or event. So while these modern console will have a familiar look about them, there’s a lot more buttons and sliders than you’re used to.  Just what are all those controls for? As more venues step up their live productions, knowing your way around a large-format console will come in handy. In the next few columns, I’ll try to demystify mixing boards.

All analog mixing consoles have pretty similar functions. They amplify and equalize signals that are then routed to various feeds and speaker systems. We’ll start at the top of a basic mixing channel strip. This single channel is duplicated over and over again on a full mixing board, making a 24 or 32 channel board rather intimidating. Just start with understanding a single channel, and the rest comes easy.

Mixer_Input_Layout_c

  • 1) Pad: This inserts a dropping resistor into the signal path to prevent channel overload from very loud signals.
  • 2) High Pass Filter: This is a switch that eliminates all frequencies below 80 Hz, which is where stage rumble usually occurs. Some boards make this a variable knob allowing you to tune the cutoff frequency from 20 Hz to 400 Hz.
  • 3) Polarity or Invert (INV): This inverts the phase of a single input channel, important to prevent phase cancellation if a microphone is facing the back of an instrument.
  • 4) 48 Volt Phantom: This turns on 48 volts to power condenser microphones and active direct boxes. Some microphones such as ribbons can be damaged by it, so only switch it on when needed.
  • 5) Gain: This is a fine adjustment for the incoming signal level, used in conjunction with the pad to get a reasonable signal level to work with.
  • 6) EQ: High Frequencies: The equalization section has at least 2 controls calibrated from -15 dB (cut) to +15 dB (boost) of level affecting different frequency bands (bass and treble) but usually has 3 or more frequency bands of adjustments (low, mid, and high). Sometimes a fourth band is added that can be varied in both center frequency and level. This allows you to sweep the control to modify the exact frequency area desired. An in/out switch allows the EQ settings to be bypassed.
  • 7) High-Mid Frequency Sweep – Selects the frequencies to be boost or cut by the High-Mid gain control
  • 8) High-Mid Frequency Gain – Sets the amount of boost or cut of the frequencies selected by the High-Mid Freq control
  • 9) Low-Mid Frequency Sweep – Selects the frequencies to be boost or cut by the Low-Mid gain control
  • 10) Low-Mid Frequency Gain – Sets the amount of boost or cut of the frequencies selected by the Low-Mid Freq control
  • 11) Low-Frequency Gain – Boost or Cut frequencies below 120 Hz or so
  • 12) EQ On/Off – When pushed in the down position, tuns on all the EQ controls of that channel. The up position disengages all EQ except for the Hi-Pass Filter (#2 above)
  • 13) Aux Sends 1 – 6: These are part of a mixer within the mixer. For instance, you may want to send a mix to the singer’s monitor cabinet that has mostly vocals, a second monitor mix for the musicians that’s mostly rhythm instruments, a full mix for the radio feed that has all the instruments (including the loud guitar that wasn’t mixed into the PA), and a mix to be sent to a digital reverb to make the room seem bigger. The more Aux Sends you have, the more you can do at once from a single mixing board. Most small boards have a least 2 Aux Sends, and mid-size boards like the Mackie 8-Bus have 4 sends per channel (6 if you count their 5/6 shift control, which I don’t). Large format consoles such as the Allen & Heath and Yamaha will often have 8 or 10 sends per channel, making them useful for large acts that require many different mixes at the same time.
  • 14) Pre/Post Select: This switch controls how the auxiliary sends work. If the Pre-Fader position is selected, the auxiliary send will get its signal from before the main Fader. This allows a stable mix to be made for the monitors on-stage that’s unaffected by the movement of the channel Faders used for the audience mix. Post-Fader select is used for a mix to be sent to a reverb or echo device. That way the proper ratio of original to effected sound will remain constant, even if the Fader is moved up or down.
  • 15) Pan: This control allow you to place a mono instrument in a stereo sound field. For example, in just the left speaker. Usually, vocals and bass are panned dead center, guitars are panned to one side or the other, and drums are spread across both channels for the big tom roll.-20dB LED: This indicator lights up to show that signal on the channel, handy for troubleshooting.
  • 16) Mute: This kills the signal to the channel Fader, and usually the Aux sends that are set for post-Fader. Most of the time, the pre-Fader (monitor) sends are unaffected. This can be a problem because even though you mute a mike in the main audience mix, it can be left on to wreak havoc in the stage monitors.
  • 17) Fader: This is the main volume control on the channel strip that affects the level of the signal being sent to the main speakers, in addition to any auxiliary sends that are set for Post-Fader.
  • 18) Signal/Clip: Usually at least a green LED to indicate -20 dBu signal, plus a red LED to indicate clipping around +12 dBu. You want to see green, but no red.
  • 19) Main/Sub-Groups: This routes the signal either directly to the main Left/Right bus, or first of a sub-group, allowing you to control all the vocal harmonies or keyboards with a single Fader on the output section of the board.From there, all the signals are returned to the output section. A good place to pick up in the next column.
  • 20) Solo or PFL (Pre Fader Listen): This places the sound from a single channel in your headphones, allowing you to cue or troubleshoot a sound from the stage without putting it in the main mix. Or you can listen to a single instrument already in the mix without disturbing anything.

Let’s take a deep breath and go onto Part II later. You’ll need to know how all these switches, knobs and faders work before you can move on to the next level.

Copyright Mike Sokol 2016
All Rights Reserved

 

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