From microphones to audio mixer to amplifier then speakers: this is the basic path that the audio takes in most live sound systems. Microphones capture audio, speakers and amplifiers reproduce it, and audio mixers serve as the "user interface". Often, audio mixers have the biggest impact; even with the best microphones and speakers, a knob in the wrong position can ensure terrible results.
Mixing consoles combine a number of inputs, typically used to connect microphones and instruments, into just one or two outputs. Outputs typically connect to an amplifier which then passes the audio to connected speakers. They may range from eight or twelve inputs up to hundreds (for example, in a recording studio).
The simplest consoles provide volume level, tone, and mute controls. The most advanced are powerful computers with digital user interfaces, the ability to save complex presets, and other high-tech features.
Below, we will cover some of the basic knowledge you should have in order to get the most out of your mixer.
Rehearsal & Sound Check
Every different arrangement of microphones, instruments, and other input sources is essentially a different system. It is helpful to do a sound check even when your configuration has not changed, but it is particularly important with a new setup. Getting your sound system configured during rehearsal will help you avoid embarrassing audio problems.
Sound check is a good time to discuss concerns with presenters, vocalists, and instrumentalists. They often have valuable experience and may have specific preferences. Accommodate their requests to the greatest extent possible and, when it is not possible to accommodate their requests, be prepared to explain why.
After an event, you should conduct another type of sound check. Seek comment from presenters and performers as well as audience members from different sections of your event space. Use the critique during your next sound check to help guide your setup and improve performance.
Fader vs. Gain
On most mixers, the fader is the control which slides up and down to adjust the volume level of an input. The gain, also called trim or pad, is typically a knob near the top of the controls for each input.
Gain affects the sensitivity of an input and it should not be used during an event. Instead, set gain levels before an event during sound check.
- Set the gain one input at a time. Begin by setting the gain knob and fader slider to zero.
- Have the talker, vocalist, or instrumentalist speak, sing, or play at a normal level. Adjust gain for the input until the indicator light next to it begins to display yellow and then lower it until it consistently shows green.
- Have the presenter, vocalist, or instrumentalist increase their loudness and, if the indicator light goes into the red range, turn the gain back until the indicator is in the green range with only occasional advancement into the yellow range.
- At this point, mute the input and begin the process again for each subsequent input that will be used during your event.
- Once you have set the gain for each input, unmute any inputs that will be used simultaneously during the event and ensure that levels are matched appropriately. If the levels do not match, make adjustments by turning down gain for the loudest inputs so that they match lower level inputs.
- During your event, use the fader sliders to make minor adjustments to accommodate variations in the sound levels of different speakers, vocalists, and instrumentalists.
- When an input is not being used, set faders to their lowest level or mute the input.
If your system was installed by professionals using proper instrumentation and techniques, the equalizer is a set-and-forget device. Unless there are major changes to the room’s acoustics or speaker system, it is not necessary to adjust the equalizer.
Minor changes to an equalizer "by ear" can have disastrous effects. Be certain that the controls on your equalizer are protected to avoid accidental adjustments. If you hear excessive or inadequate bass, make adjustments on the audio mixer by adjusting the tone/EQ knob for each input.
For audio systems that are primarily speech, you can avoid the complex requirements of running a mixing console with an automatic microphone mixer (automixer). In many cases, this type of mixer can eliminate the need for a live sound operator altogether and they may even provide better results than an operator.
An automixer is essentially a computer that listens to all inputs and turns on microphones when they are needed. It can automatically mute or turn down input levels when connected sound sources are not in use. The largest advantage of an auto mixer is that it optimizes the number of open microphones. The effect is increased volume without feedback. Auto mixers can also lower hiss, rumble, reverberation, and other noises that may occur when multiple microphones are used simultaneously.
A mixing console is recommended when mixing singing, instruments, and media playback (such as from CDs or DVDs). Some advanced mixing consoles may have automixer capabilities built-in while others may support adding an automixer as a supplement. In addition, many automixers are included in digital sound processors (DSPs). DSPs provide even more advanced features such as built-in equalization.
If you would like to learn more about any of the topics we have discussed, the Shure Educational Publication below, Audio Systems Guide for Houses of Worship covers many of them in detail. In addition, we would appreciate the opportunity to answer any questions you may have about mixing consoles, automixers, or digital sound processors.Download PDF