How to Operate a Sound System Mixer
Mixing consoles are sold with different numbers of channels. If you know what one channel does, all other channels are the same. All the channels then feed into a master section. This makes the mixer is less intimidating.
Lets start at the top of the mixer channel 1.
Usually located at the top of the channel strip. This controls how much signal is coming into the mixer. You can also think of it as sensitivity. This is usually set around 11 o’clock or so. However, there are no exact rules on where they should or should not be set. If there is a peak light per channel(sometimes located above the fader) it comes on to indicate you are sending too much signal. It indicates clipping, which can result in distortion. This can be reduced using the gain at the top of the channel.
Microphone or line level
Button located at the top. This button chooses weather you are plugging in a microphone or a line level device such has a CD player, DVD player, iPod, Etc.
It looks like a circle with a line thru it. This button will throw the signal out of phase(flipping positive to negative). Most cases this should not be used. An example of correct use: miking a snare drum with a microphone on top and one below. You would throw the bottom microphone out of phase to keep the sound from canceling itself . Other than certain scenarios, all microphones need to be in phase for a clean mix.
Phantom Power 48+
This is the power supply for electret condenser microphones. Some microphones require phantom power to operate, such has choir, podium and some vocal microphones. Phantom power will not affect other microphones that do not require it. Lower cost mixers will only have one 48V switch which could be located in the rear of the mixer. Other mixers will have it on each channel strip.
The EQ section is used to ‘tailor’ the sound to your desires. Typically mixers have bass and treble (also called high and low, LF, HF, and others)adjustments, which adjust the frequency by shelving. This is similar to your car radio controls. Some mixers have fixed mids, and others have sweepable mids. The sweepable EQ allows to to pick a frequency, and then cut or boost them.
Aux mixes are adjusted separately than the main mixer. They are useful for creating monitor, recording, and other mixes. There are 2 types of auxes: pre-fader and post-fader. Some mixers are fixed, others are selectable by buttons. Pre-fade means the signal is taken before the fader, and the fader will not affect the signal. When you move the fader volume up and down it will not affect the volume of your aux. In post-fader mode, changing the volume of the fader will also change the volume of your aux, since the signal is taken after the fader. You will use the pre-fader mode for your stage monitors, that way the artists mix is not affected by the control of the house. The post-fader mode is used for recording, and effects such as reverb. The signal is taken after the fader, so movements make in the house follow through to the aux. Your recording can have fade ins and your effects can stay proportionate. In the Master section, there are overall ‘aux masters’ for each row of auxes.
Left and Right Stereo Pan
If you are not using sub faders, the pan knob should stay in the middle, to ensure the same mix comes out of the left and right speakers. This is desirable for PA settings. This assigns the channel to the left or right sub faders. Some mixers will also have a mono output. Your mixer may have subgroup faders, which the channel may be assigned to the individual sub groups or left and right to all outputs. To assign to sub group 1 you would push down the button labeled 1 & 2 and turn your pan knob to the left, sub group 2 you would turn your pan to the right. Sub groups 3 and 4 would use the 3&4 button and pan in the same manner.
PFL ( Pre-fade listen) Button
This button is used to monitor individual channels in headphones. Regardless of mute, volumes, house settings, you are able to preview the signal. There will be a light in the main section (and each channel) indicating the PFL status. You can monitor more than one channel at a time. When you are not monitoring a channel you will have the ability to hear the entire mix in your headphones. Individual channels can be isolated for closer inspection. If you have a mixer with AFL (After-fader listen) you can listen in to isolated mixes.
Rides in the fader slot up and down to control the volume in the main output.
This is the basic principal of an analog sound mixer channel. Once you know the workings of an analog mixer, this knowledge can be applied to digital mixers.
Most importantly: Take the time to play (in real time, rehearsal?) with the mixer so you may expand your knowledge.
Denny Phillips CTS, Leed AP
Phillips Pro Systems