Live Sound Reinforcement Mixers

Live Sound Reinforcement A mixer is the center of the live sound reinforcement system and is sometimes referred to as a sound board, or mixing console. The mixer allows multiple audio inputs to be combined and rerouted to multiple output devices and provides a basic degree of control over signal characteristics.

Live Sound Reinforcement Mixers are designed to allow the signal strength to be controlled in several stages. The first stage, input attenuation regulates the signal to allow adequate signal strength (pre-amplification) without overloading the channel. Many mixers will also provide impedance matching inputs for either a balanced or unbalanced line (cable), these are the mic inputs.

Live Sound Reinforcement The mixer has controls for gain, volume, fading and panning for each of the input channels, most mixers will also provide switchable phantom power for condenser mics.

Live Sound Reinforcement We’re going to look at an input channel in detail and discuss the function of each control knob.

Live Sound Reinforcement If we look at the top section of channel 1 you’ll notice that there is either an XLR or TRS input. Input channel 2 with an XLR mic input or a TRS bal. or unbalanced input. Pre-amplification takes place here. All of these channels are mono inputs that will eventually be sent to the stereo outputs. This is the same as gain. The 2 scales refer to either XLR +10 to +60dB or the TRS input +10 to -40dBu

Live Sound Reinforcement Gain or Trim is the ratio between the power of the input signal and the output signal, whereas volume is the loudness of the output signal. Gain and fading should not be confused, gain is used to describe the strength of a signal before it is enhanced by an amplifier or preamplifier.

Live Sound Reinforcement The middle section of each channel contains a 3 band equalizer. The 3 EQ bands provide cut or boost from -15dB to +15dB In the center position “0” the EQ is inactive The low cut filter eliminates noise from wireless mics and sub sonic noise or explosive sounds from mics.

Live Sound Reinforcement The lower section of the mixing channel has the effects control, stereo position control and volume/fader control. The FX sends the mono channel to the effects processor section of the mixer and provides up to 15dB gain. The pan control determines the position of the channel signal within the stereo image and maintains the signal at a constant level. The clip LED illuminates when the input signal is driven too high, use the trim control to reduce preamp level till the LED goes out. The level control determines the volume of the channel being sent to the main mix, similar to a fader. This will need to be increased if using the FX control.

Live Sound Reinforcement The stereo inputs provide a means for connecting keyboards, effects processors etc., these channels can be used as a mono channel by using the left input, each stereo input also has an FX section. The left input is the mono channel, these inputs are both balanced and unbalanced.

Live Sound Reinforcement This is the FX section for each of the stereo inputs and operates similarly to the FX section of the mono inputs. The +4dBu & -10dBu switch is a sensitivity switch that selects between either +4dBu or -10dBu. Stereo channels that are controlled by the FX section.

Live Sound Reinforcement So far we’ve looked at the input channels on a mixer and the signal controls available for each of the channels. The trim as you’ve seen is an attenuator and is used to increase the signal strength, the signal is then processed through the onboard EQ to refine the sound and then the signal can be sent to the effects (FX) section of the mixer and you can choose to have the input signal appear in the left or right channel of the stereo output.

Live Sound Reinforcement The different input channel signals will all be sent to a signal line called a buss, a buss is a way of carrying a group of individual signals along a common route. The destination of the input signals is sent from the buss to a combining amp (summing amp) and then the mixer puts out a signal which represents the combination of all the signals into that buss.

Live Sound Reinforcement The FX send outputs the signals from the input channels, this can be connected to an external effects device. The Phones connector is for head phones. The Main out connectors are mono and are for connecting external equipment, your EQs, compressor and speaker amps can get connected to these outputs.

Live Sound Reinforcement The control room out connectors carry the summed effects and main mix signals as well as soloed channel signals and can be sent to a CD/MD (mini disc recorder) player/recorder. RCA connectors

Live Sound Reinforcement THE RED LIGHT TURNS ON WHEN PHANTOM POWER IS ON. THE BLUE LIGHT IS THE POWER LIGHT. THESE LIGHTS DISPLAY THE SIGNAL LEVEL. ASSIGNS THE CD/TAPE INPUT TO THE MAIN MIX PROVIDING ADDITIONAL INPUT FOR TAPE MACHINES. 0dB IS RECOMMENDED FOR ALL LEVELS. MONITORS THE CD/TAPE INPUT VIA THE CTRL RM AND PHONES OUTPUT. USED TO MONITOR EFFECTS ONLY IN YOUR HEADPHONES AND CANCELS OUT THE MAIN MIX SIGNAL. ADJUSTS THE VOLUME OF THE MAIN MIX FROM THE MAIN OUT OUTPUTS. CONTROLS THE SIGNAL LEVEL OF THE PHONES/CTRL RM OUTPUTS.

Live Sound Reinforcement The effects processor offers 99 presets and using the FX control, signals can be sent into the processor. THE CLIP LED SHOULD NOT BE A STEADY LIGHT, IT SHOULD ONLY LIGHT SPORADICALLY. THE SIGNAL LED INDICATES THE INPUT SIGNAL IS STRONG ENOUGH AND SHOULD ALWAYS BE LIT. THE PROGRAM CONTROL SELECTS THE TYPE OF EFFECT, THE PRESET BLINKS UNTIL YOU PRESS THE BUTTON TO SELECT IT. THESE ARE THE EFFECTS ASSOCIATED WITH THE PRESET NUMBERS. THE FX TO MAIN FEEDS THE EFFECTS INTO THE MAIN MIX.

Live Sound Reinforcement We just looked at all of the channels and controls for the Xenxy 1202FX mixer and how they work together to process incoming signals. The fader is normally placed at the bottom of the channel or close to the operator in almost all mixers. The clip LEDs are instrumental in maintaining a good undistorted signal throughout the signal processing.

Live Sound Reinforcement Mixers are usually describe by the inputs and the outputs to their buss structure. The Xenxy 1202FX is a 12 input, 2 output mixer with a built in effects processor (FX). Let’s look at the difference between a mic channel and a line channel.

Live Sound Reinforcement Notice the mic is plugged into the XLR connector of channel 1 and the guitar amp is plugged into the TRS port (line level) in channel 2. The keyboard is plugged into the stereo inputs.

Live Sound Reinforcement The speakers for this set up are plugged into the control room out ports, these are passive speakers.

Live Sound Reinforcement This set up is similar except the EQ, X-over amp and speakers are connected to the “main out” ports.

Live Sound Reinforcement What is the difference between the trim and fader controls? Is a gain control the same as a trim control? What is a level control and is it the same as a fader control ?

Live Sound Reinforcement The trim and gain controls are the same, gain is an attenuation function that increases or decreases signal strength based on voltage. The fader and level controls are the same and they control volume, the main mix slider controls the complete mix volume.