Understanding Audio Mixers: The Heart of Sound Control Systems

1. Mixing Consoles Designations Inputs Outputs Signal processing

2. Sound Control Mixer - Heart of the Audio System • Mixer - Heart of the Sound system • Sound Board, Audio Console, Mixing desk • Main tool of the operator (Board Operator) • Basic Purpose - Controls • What is it - Selects audio signals from various sources • Devices are connected to input channels • Microphones • Output channels of CD players, MD players, DAT players, computers • How Loud will it be - Controls signal level (volume) • Where is it going - Sends audio to various locations • Devices are connected to outputs • Power amplifiers • Input channels of MD players, DAT players, Computers

3. Sound Control Mixer - Heart of the System • Mixer Nomenclature (Functional Description) • 8x2 = 8 inputs and 2 outputs • 16x4 = 16 inputs and 4 outputs • 16x4x2 = 16 inputs, 4 group of sub outs, 2 main outs. Can be used as: • 16 ins mixed down to 4 sub mixes, mixed down to 2 output channels (recording studio or concert presentation) utilization • 24x6 (Theatre type utilization) • 16x4x2x1 – adds a mono output • Also can be referred simply by the number of input channels ex. 8, 16, 24, 48 etc…

4. Mixer Amp Upstage L/R MD 1 MD 2 Amp Cass Cluster Computer Amp Radio Record Player Cue Control Audio System – Sources, Control, Destinations Equipment System is the Primary Tool of Modern Theatre Sound Design: • Block Diagram - Foreigner Setup 1 - 2 L/R Mono 3 Group/ Outs 1-2 3-4 5-6 7-8 Input Channels

5. Input Buss • This is the section where audio signals from microphones and/or playback equipment enters the mixer • This is the area where impedance matching and Balanced / Un-balanced lines must be carefully watched • The input buss typically starts at the rear of the console with either XLR or ¼” TRS connectors

6. Input Buss

7. Input Buss Rear view of a Mackie t24

8. Input Buss • The front side of the console will differ from manufacturer to manufacturer but they will have most of the same components • The input channel will usually be arranged to follow the virtual signal path

9. Input Buss • Pre-amplifier • Pre-amp, trim, trim pot, gain • Used to bring a microphone level signal up to line level for easy manipulation within the mixer • Also used to adjust the line level inputs from other sources • Pad or Attenuator • A switch which will lower an inputs level by a set amount • Usually used in an input device is too “hot” or much too high a level

10. Close up of Pre-amp section Input channel # Pad / low end roll off Gain adjust

11. Equalization section • Onboard equalization control will vary greatly • Simple “tone” control • Simply varies the balance between high and low frequencies • Treble and Base • Boost or attenuate high frequencies (treble) or low frequencies (base) • Only adjusts a preset range of frequencies • Hi – Mid – Lo • A fancier version of treble and base control • 5 band EQ • Able to boost of attenuate 5 different ranges of frequencies • Parametric EQ • Able to select which frequency range to control and then boost or cut it

12. Equalization section High freq. control High-mid with selectable frequency range Low-mid with selectable frequency range Low frequency control

13. Auxiliary Sends • Next in line comes a number of Aux sends • Typically 4 to 8 individual busses • Some or all will be pre or post fader selectable • Pre-fader – the signal strength (volume) coming from the aux send channel will be independent on the position of the channel fader • Post-fader – the signal strength coming from the aux send will be dependent on the position of the channel fader • Often labeled as PFL (Pre-Fade Listen) • Often used to send signals to other devices • External effect processor • Reverb or echo • Monitor amp/speakers for performers

14. Auxiliary Sends Note the pre-fade switch 8 individual aux send channels

15. Signal Routing • Each input channel will be assignable to one or more output channels • Very often one selector button will assign the input to two separate outputs • 1-2 or 3-4 for example • The Pan Pot (Panoramic Potentiometer) adjusts the level of signal going to each of the pairs • Example: With the pan pot centered and 1-2 selected, the entire signal is sent to outputs 1 and 2 equally. If you turn the pot to the left, more signal will be sent to output 1 than output 2 • This is usually to be avoided for theatrical use • Look for single output selection control if possible • PFL – Pre-fade Listen. Sometimes called “solo” • Usually available to send the signal to a studio monitor or headphones to allow operator to listen to channel without having to send it into the house • Channel Mute – turns the channel off. Useful when using wireless mics

16. Signal Routing Pan Pot Output selection Mute Note: PFL not available on this model

17. Other input controls • Phantom power • A 48v DC power supply applied to the mic input lines • Used to power condenser mics (to be discussed later) • Phase reverse • Inverts the signal coming to the inputs • Used if pins 2 and 3 on a mic cable are reversed for example • Ground lift • Removes the ground connection at the console from the input cable • Used to help eliminate ground-loop noise • To be discussed during troubleshooting

18. Output Section • This is the area where audio signals will leave the mixer, heading toward • Effects processors • EQs, delay units, reverb units, recording devices • Power amplifiers and eventually loudspeakers • Output plugs will typically be • Balanced XLR line level • Balanced TRS line level • Unbalanced ¼” phone plug line level • Unbalanced RCA plug line level

19. Output Section Left, Right and Main outputs Sub or group outputs Auxiliary outputs

20. Output Section • Sub-group output faders • Sometimes called groups, subs or submasters • Act as a master fader control for any inputs assigned to it • Typically these are cabled to power amplifiers • Main outputs • Sometimes called Left-Right, Stereo or Mix • Essentially two additional outputs, where the manufacturer has taken a guess as to what the end user will use them for • Sub groups can usually be combined and selectively assigned to the main output • Master output • Sometimes called Mono • The main outputs can be combined together and controlled from one master fader

21. Aux-Output Section Aux out mute switch Aux out gain control After fader listen

22. Group-Output Section

23. “Flying Faders” • Automated mixers are becoming more and more common • Started simply to record levels in recording studios • Often had 60 or more inputs levels to write down and could have many many setups. • Flying faders would remember where the faders were set and you could restore to any setting with the push of a button

24. “Flying Faders” • Today mixers are capable of remembering output selections, EQ settings, pan settings etc. • For live mixing it is REQUIRED to still have actual faders which an operator can move • Performers will never do the exact thing every night • The board operator must be able to easily make adjustments to levels on the fly

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