Each input that comes into the sound board is connected into a “channel” of the mixer board. These channels have multiple controls that are used to control the input that comes from the device that is connected to that channel. In this section, we will discuss the TRIM/GAIN/LEVEL control.
The controls on that channel are often referred to as a “Channel Strip”. The contols on each strip will be identical except for any channels that are designed for devices such as tape/CD players or other devices which typically reside in the sound booth and output stereo sound. We will examine the typical channel strip which will control a microphone or instrument input. The channel strip used in this training will likely not be exactly like the one that you use, but the controls will be typical of channel strips on most mixers and the discussion should translate easily to the board that you use.
At the very top of each channel strip, there will usually be a control called “Trim”, “Gain” or “Level”. This control is used to set the base input level for the microphone or instrument. This level setting is critical to the proper operation of the mixer and is probably one of the most important controls on the board. If the level is set too low, you will limit the dynamic range (volume level) of the device. If the level is set too high, the device will clip (or distort). While clipping can occur at many places within the mixer, if the signal is clipped here, it will be produced throughout the mixer.
If your mixer has an input level meter for each channel, the level should be set so that the meter barely touches the “Red” when the device connected is being output at it’s loudest level.
If your mixer has a “clip” light (usually red), the level should be set so that the light comes on only very briefly when the device is at it’s loudest.
If your mixer has no input level indicators, follow this procedure to set this control:
- Make all devices (microphones or instruments) other than the one connected to the channel in question are muted or their volume level sliders are turned all the way off.
- Set the Level control to zero
- Set the volume slider to unity zero (see volume slider control if you don’t know what this is)
- Set the “Master Volume” in the output section to unity zero.
- If the device connected is a microphone, have someone talk into the mike at a very loud level. If it is an instrument, have someone play the instrument at the loudest volume that they will be playing.
- Turn the level control up until the main level meters show activity that is 3/4 of the way to the “Red” level. Note: You may need to set other controls (like the group) in order to get output to the mains.
Once this control is set correctly for the particular instrument or mike, it should not be adjusted. One of the mistakes that rookie sound people make is using the gain control as an overall level control for the channel. That is not what this control is for and using it in this way WILL cause problems in your mix. Set it once and LEAVE IT ALONE. (OK, there are times when you may have to adjust this … like when the person who is playing the instrument or singing into the mike is a lot louder than they were during the setting of the control. But, the principle of this control is that it is not used to adjust the volume of the channel … it is only to set up the input level)
You should go through the process of setting the gain level for each channel whenever there is a change (like a different person singing into a mike, or a different instrument connected to the channel).
Setting this control properly will make the running of everything else easier. If the gain control is set incorrectly, you will not be able to correct it, only mask it.
Go to Lesson 3: Aux Controls