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Michael Drolet -- 2010




There are many terms used to refer to the complicated-looking piece of electronic gear sitting on the table in front of the Sound Booth window:

console, mixer, mixing board, sound board, mixing desk, sound desk.

[I will try to be consistent and to always refer to the mixer.  If  I slip up, you now know the other possible terms.]

In a production studio, the mixer is used to route sound signals from various sources, (microphones, CD players, FX units) to various destinations (usually tape machines, hard disk recorders or FX units). It can also be used to modify the tonal quality (EQ) or relative balance of the sound signals passing through it.

In a performance space, the mixer serves to route the various sound sources (microphones, CD players or FX units) to various loudspeakers on the stage or throughout the house. It allows you to control where the sounds will be heard and how loud they will be.

The same mixer will generally serve for either the production studio or performance space.  One of the mixers we have at John Abbott is a MACKIE ONYX1640i MIXER, manufactured in the U.S. It is representative of mixers you will find in many production studios or theatre spaces today.

In addition to its use as a live sound mixer, the 1640i also can also serve as a bidirectional, 16 channel sound interface for a computer.  A single Fire Wire cable connects the mixer to the computer. Sections involving Fire Wire are highlighted  like this one.

Mackie Oyx 1640i



In a sound system,  a source of sound is referred to as an output.  A destination is referred to as an input.
Building a sound system involves connecting sources to destinations  --   an output to an input to an output to an input.....and so on.

The sources could be the outputs of mics. on stage, CD players,  effects units or tracks from a computer.

The destinations could be the inputs of the House speaker system, onstage monitors, headphone amps or effects units.

The MACKIE mixer allows you to simultaneously control and route, any (one or more) of sixteen sound sources  to any of six main destinations; the MAIN MIX, SUB1-4 outputs and/or to any of  six auxiliary destinations; the AUX1-6  outputs.

In a sort of technical short-hand, this mixer may referred to as a 16:4:2 mixer (with 6 auxiliaries) to indicate it offers 16 inputs, 4 subs and 2 main outputs (with 6 auxiliaries).

Onyx line

Although the mixer may appear to be complicated, it is in fact, composed of only a few different building blocks or strips. Each type of strip groups together all the controls and internal circuitry to perform similar functions. In our mixer, the 16 input strips are grouped together on the left side of the mixer. The 4 sub strips  and single main strip are on the bottom right. The monitor and aux master strips  are located above the sub and master modules.

You will only need to learn the operation of these few strips, in order to "master" operation of the entire mixer.

We'll have a look at the front panel controls and the signal flow through each of the modules in turn.


The 16 mono input modules or strips, to the left of our mixer, are indicated by white fader knobs.

The "LINE/FW" switch selects either the analog input or the digital return from the computer as the source to the input channel.

Onyx Input

Some condenser or electret type microphones can be powered externally, eliminating the need for batteries. The power required can be supplied by the mixer via the same cable used to carry the microphone signal to the mixer.

This system is called phantom powering. The "48V" switch on each input channel  activates this function.  The LED  above the switch  indicates that phantom power is activated for that channel.

In certain cases, supplying 48 volt power to a microphone not requiring it  may result in noise or hum (at best) or damage to the microphone (at worst).

Phantom powering should only be activated if you know you need it for a given microphone.


LOW CUT (High Pass Filter):

  • cut 18dB/octave from  75Hz
  • can be used to cut traffic or air conditioning rumble
  • don't use on bass guitars or tubas.


Input channels 1 and 2 have an additonal switch to configure the input to accept the output of a musical instrument  (guitar, keyboard).

Onyx DI switch

The "GAIN" control allows you to adjust the input strip so that you can operate with the white channel fader in its normal range, around "-U-" on the scale. This assures that the signal will have the maximum headroom and minimum noise.  (See "SOLO" button below.)

Headroom is the level difference available between normal level and the point of distortion.

Noise is the background hiss you hear when you turn the gain or volume up too much.

At the "-U-" setting, there is still 10 dB of gain available, should the input signal drop in level. We say that there is 10 dB of gain-in-hand. This gives you room to maneuver should the input signal change.

Working at "-U-" also allows for smooth fades in or out.


Input Channel EQ:

The FireWire "SEND" switch selects the feed to the computer either PRE or POST EQ -- before or after the action of the channel equaliser.


Onyx HI EQ


  • boost or cut 15dB @ 12kHz

Onyx EQ



  • boost or cut 15dB
  • sweepable  centre frequency from 400 Hz to 8kHz



  • boost or cut 15dB
  • sweepable  centre frequency from 100 Hz to 2kHz

Onyx LO EQ


  • boost or cut 15dB @ 80Hz



Allows the operator to activate or deactivate the equaliser on each channel.

AUX Sends:

The controls labeled "AUX" allow you to send a part of the signal from any input channel strip to any of six additional outputs. These outputs can be used to feed a separate mix to program sound, monitors onstage, headphones in the studio, or to the sound processing and effects devices in the control room.

AUX sends can be taken before or after the channel fader.  We call these feeds PRE fader or POST fader. 

POST fader sends are used to feed reverb devices where you would want the strength of the reverb effect to follow the level as controlled by the channel fader. 

PRE fader sends are for feeding headphones for instance. You wouldn't necessarily want the mix in the headphones to change as you trim the recording or house levels.

On the Mackie 1640i, global switches on the AUX MASTER strip select  PRE or POST fader operation for each of the AUX busses.  That means that all of the input channels feeding a particular AUX buss will be either PRE or POST.

Onyx AUX send

Routing Section:

Onyx PAN

The "MUTE" button de-activates the entire input strip.

Light emitting diodes (LED) labeled "-20", "0","+10", and "OL" indicate the level of the input signal. "OL" stands for OverLoad.   If the "OL" LED flashes briefly every couple of minutes, the signal level is not too high. If it flashes continually, you will have to reduce the input signal to avoid distortion.
  • adjust the "GAIN" control down (counter-clockwise)
  • insert an external attenuator (pad) at the input connector
  • move the microphone farther from the source. 

The signal level indicated is independent of the position of the input fader and allows you to roughly set the position of the "GAIN" control to an  optimum position.

The signal passing through the input strip can be routed to the Left and Right  MAIN MIX outputs by pressing the "L-R" button. The "PAN" control (short for panoramic potentiometer) allows you to send the signal to anywhere in the sound field between the left and right outputs. The buttons "1-2", "3-4", allow the signal to be sent to any pair of sub outputs.

The odd numbered outputs are arbitrarily considered as left and the even numbered ones as right. If you depress the "1-2" button and pan fully left; the signal will go only to SUB 1.  Panning right will assign the signal to SUB 2 only. Midway between left and right will assign the signal somewhere between SUBs 1 and 2.

The white sliding control is the input channel fader. This is your operational control over the signal level during a recording or performance. It allows you to smoothly fade an individual sound in or out.

The "SOLO", button routes the input signal directly to the left/right meters and monitor speakers (or headphones) and illuminates the large red indicator labeled "RUDE S0L0".  These meters have much greater resolution than the four LEDs on the input channel.

 With "SOLO" in, start with the "GAIN" control fully counter-clockwise. As someone talks into the microphone or while you play the loudest cut of your show CD;  rotate "GAIN"  until the meters are just reaching  the -0- VU point.

Don't forget to release the "SOLO" button afterwards!

  (Look for the "RUDE S0L0" light.)



The four SUB (sub master) faders are located on the bottom right of the mixer.

In theatre, we usually use the SUBs as discrete outputs -- to feed four more loudspeakers.

For recording purposes, each SUB can be independently assigned to either or both of the Left or Right MAIN MIX busses.


The "SUBS TO FW 5-8" switch allows the 4 SUB outputs  to be sent to the computer on channels 5-8. SUB FW58


The "ASSIGN TO FW 15-16" switch allows the MAIN MIX output to be sent to the computer on channels 15-16.


The "MAIN" fader controls the signal from the MAIN (L-R) output. MAIN FADER

{White Space}


The mixer's built-in microphone "MIC" allows you to talk to the talent through headphones or stage monitors.

The "DESTINATION" switches determine where the talkback signal will be sent -- headphones plugged directly into the "PHONES" jack on the console or headophones or stage monitors plugged into one or more "AUX 1-6" outputs.

The "LEVEL" control allow you to adjust the talkback volume heard by the talent.  Start withthis control at minimum and slowly increase it while holding the "TALKBACK" button; until you are clearly heard.
onyx talkback


The "SENDS 1-6 TO FW 9-14" button routes the AUX SENDS via Fire Wire to inputs 9 to 14 of the computer software. onynx FW masters

To the left are the "AUX SEND 1-6"  master controls. The "SOLO" buttons route the respective AUX signal to the control room monitor. The "PRE/POST" buttions determine if each AUX is sent pre or post  (i.e. before or after)  the AUX SEND master controls.

aux masters


To the right are the four stereo  AUX RETURNS.  These allow you to send the stereo outputs (returns) of four separate FX processors to the MAIN MIX outputs.

AUX RETURNs 1 and 2 can be returned to AUX SENDs 5 and 6 respectively, in addition to, or instead of, the MAIN MIX.  This  could be used to send reverb to stage monitors, for instance.

AUX RETURN 3 can be returned to the MAIN MIX, or to SUBs 1-2 or 3-4.  We can use SUB 3-4 to add reverberation to the ROH (Rear Of House) speakers, making the theatre sound more "live".

AUX RETURN 4 can be sent to the MAIN MIX, or only to the Control Room and Phones outputs.  This way, the audience won't hear it.

The POWER LED indicates that the mixer is powered.
aux rtns


"CTRL ROOM/PHONES SOURCE" buttons select the source for the Control Room monitors:

  • SUB 1-2
  • SUB 3-4
  • TAPE (external)
  • FW 1-2
The "L R" meters indicate the level of the sources selected by the  "CTRL ROOM/PHONES SOURCE"  buttons or of  the source(s) "SOLO"ed.


"FW 1-2" sends Fire Wire 1-2  outputs of the computer only to the "CTRL ROOM/PHONES".
"ASSIGN TO MAIN MIX" sends Fire Wire 1-2  outputs of the computer directly to the Main Mix.

"CONTROL ROOM" sets the volume for the Control Room monitor speakers.

"PHONES" (headphones) sets the volume for the  "PHONES" jack.

"TAPE IN" adjusts the volume of the external "TAPE IN" signal. "TAPE TO MAIN MIX"  feeds it to the "MAIN MIX".

The large red LED labelled "RUDE SOLO" indicates  one of the "SOLO"  buttons has been activated.

The "SOLO LEVEL" controls adjusts the volume of the "SOLO" buss.

There are two SOLO modes on the Mackie,

  •  "AFL" or "SIP"  (Solo-In-Place) and
  •  "PFL" or "LEVEL SET". 

The "SOLO MODE" button selects between the two. We normally use "PFL".




Audio signal levels fall into one of two categories.

  • Microphones, electric guitars and other electronic instruments generate very low level signals; on the order of a few millivolts -- thousandths of a volt. These are called microphone level signals.

  • Tape recorders, CD players, FX units and most other professional studio equipment, all generate much higher signal levels -- several tenths of a volt or more. These are called line level signals.

There is a difference of 40 or 60 decibels (dB) between microphone level and line level signals.

Either type of signal must be connected to the mixer via the appropriate jack or socket.

  • Connecting a line-level output to a mic-level input will result in distortion.
  • Connecting a mic-level output to a line-level input will result in an unusably low (quiet) signal.

Microphone level signals connect to the three-pin XLR-type female connectors. Line level signals connect to the 1/4 inch TRS jacks.

DO NOT connect to both on the same input channel.

input connectors


Connect to outputs of FX processors.

aux return connectors


Connect to inputs of upstage, ROH loudspeaker systems.



Connect to Control Room (Booth) monitor speaker system.

onyx cr out


Left, Right connect to inputs of proscenium (FOH) loudspeaker systems. Mono connect to Centre FOH.



Connect to inputs of FX processors, stage monitors.


Connect to computer Fire Wire card.

onyx fw conn


onyx 1640i block


Mackie Onyx 1640i -- Track Sheet -- Print these sheets to record your show presets.

Mackie Onyx 1640i -- Block Diagram

Mackie Onyx 1640i -- Fire Wire I/O

Mackie Onyx1640i -- Owner's Manual -- Read this attentively to really understand the mixer's operation.

Mackie Onyx1640i -- Quick Start Guide -- Consult this link in a panic.