What is a Mixing Desk For?
A mixing desk allows singers and musicians to be mixed together to create a “well balanced mix” before being fed to a PA system or a multi-track recorder. A mixing desk is designed to take a range of different signals such as Mic Level, Line Level and sometimes Phono Level and allow you to correctly input and mix them together.
What is Mic & Line Level?
Mic Level
Mics convert the noise from a voice or an instrument into an electrical signal that then needs to be boosted by a mixing desk before being sent to a PA system. This electrical signal is a very low voltage and should be connected to a dedicated Mic Input on the mixing desk. The mic input is normally a 3 Pin XLR type connector but sometimes it might also be a Balanced TRS ¼ jack type connector (normally only on budget mixers).
PLEASE NOTE, the level from a pick up on an acoustic guitar/violin etc and also a turntable is also mic level although a turntable should be connected into the phono input (provides correct eq).
Line Level
This is generated by electronic instruments and components such as Keyboards, CD or MP3 players, Mixing Desks, DJ Mixers, Line output from a Guitar Combo, Radio Mic receiver etc. Line level is a higher voltage than mic level and should be connected to the Line Input normally a TRS ¼ jack type connector on the mixing desk.
PLEASE NOTE, Some mixing desk have a PAD switch near the mic input that when engaged allows a line level to be connected into a mic input. If you do not have this switch you should always connect a line level signal into line input as you will overload a mic input and cause distortion. Also should you try and connect a mic signal into a line input you will find the signal very quiet with a lot of “Hiss”.
How do I know which one to choose?
Mixing Desks have a combination of Mic and Line inputs and so you need to look at what you are trying to connect into it. If you do not have any line level sources such as Keyboards, Guitar combos etc then you need to have a mixer with enough mic inputs to accommodate your needs. Alternatively if you are using backing tracks from a CD Player and keyboards only then you need more Line Inputs. Typically mixing desks start from about 8 channels and will often have 8 mic and line inputs and you select what input you need.
For example a band with the following set up: drums, bass, keyboards, lead guitar with two singers would probably want inputs as follows:
Drums (mics for kick, snare, hi-hat & overhead) = 4 mics
Bass (line out from bass combo) = 1 line
Lead guitar (line out from guitar combo) = 1 line
Keyboards (Stereo line out keyboard) = 2 line
Singers (2 x mics) = 2 mics
Total number of channels required is: 10 inputs of which there needs to be 6 mic inputs & 4 line inputs
Mixing Desk Controls
The controls you will normally find on a mixing desk starting from the top are:
Gain/Trim Used to set the correct level into the mixing desk
EQ Used to alter the tone of the sound
Aux Used for sending the signal to stage monitors or an effects processor such as a reverb unit
Pan Used for directing the signal to the left or right side speaker stack
PFL Button (pre Fader Listen) When switched on indicates the level of the signal coming into that particular channel on the main output Meters whilst allowing other channels to still be heard
Solo Button Similar to PFL except when it is switched on it just allows that channel to be heard
Channel Fader Used for setting the volume for that particular channel when creating a mix
Main L/R or Mix Faders Used for setting the overall “mix volume” to be sent to the PA System
Powering Up
The rule when powering up your equipment is that you should always power up your mixer before the amplifier and then when powering down it should be the amplifier off first and then the mixer. By powering up the mixer first you prevent any popping sound that might generate being amplified and possibly damaging the PA system. By powering down the amplifier off first you again avoid any noise the mixer on/off switch might make being amplified through the PA system.
PLEASE NOTE when powering up down, it is always a good idea to make sure amplifier volumes and mixing desk faders are all turned down before actually engaging the on/off switch.
Getting Going
Having connected your mixer to the amplifier and speakers as shownpower up the mixer first and making sure the all the faders are down, power up the amplifier afterwards
Having chosen an appropriate Mic (see our “Understanding Mics” tech Sheet) and using a standard XLR type lead connect the female end to your microphone and the male end into the mic input on your mixing desk. If the mic is a condenser type then you will need to provide power to it using an internal battery or by pressing phantom power on the mixing desk.
If your desk has a mic or line select switch then select mic
Next make sure all the EQ pots are in the centre “flat” position or the EQ bypass button is engaged.
If you have a PFL or Solo switch (normally located just above the channel fader) then engage this.
Position the mic near to the instrument or singer and either get a sound to be generated or ask the person to sing. (Please note that it is important to ask the person playing the instrument or singing to perform at the volume they would do when playing live).
Setting the Gain
Whilst this is taking place adjust the Gain/Trim control at the top of the mixing desk so the level comes up to about 0dB on the meters. Then If you do not have a PFL/Solo button then turn the gain up until the clip light starts to flash then wind it back approx 4 – 5 dB.
Next bring the channel fader up to the “0dB” mark. This represents Unity Gain which essentially means the level is the same as what you have set the gain to.
If your channel fader has a stereo or L/R button engage this and this will route your signal to the main L/R outputs. If it doesn’t have this button it should route it automatically.
Assuming your amplifier is connected to your PA speakers and is turned up, you can now start to bring up the main L/R mix faders on the mixing desk and should start to hear some sound!
For Line level Signals repeat the process except ensure you connect you line level source (normally a ¼” TRS Jack type connector into the line level input on the desk.
PLEASE NOTE you should never bring up the main mix faders much above 0dB or to a level that causes tha amplifier clip lights to illuminate as this represents the max volume the amplfier can take and exceeding this will cause distortion which in turn will lead to “blown speakers”
Trouble Shooting
Got No Sound?
Check the mixer and amp is powered up and the amplifier volumes are turned up
Check the mixer is connected form the main outputs into amplifier inputs
Check the speaker leads are connected from the amplifier to the speakers
Check the channel fader is tuned up
Check the main outputs on the desk is turned up
Try a different channel on the desk
Try a different mic lead