INTRODUCTION:

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:

[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 send 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 send 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  SOUNDCRAFT SIGNATURE 22 MTK, designed in great Britain and manufactured in China. It is representative of mixers you will find in many production studios or theatre spaces today. 

SOUNDCRAFT SIGNATURE 22 MTK MIXER:

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 SOUNDCRAFT SIGNATURE 22 MTK mixer allows you to simultaneously control and send, any (one or more) of twenty-two sound sources  to

• any of four intermediate destinations; the GROUP outputs, and/or to
• either of two main destinations; the MASTER outputs, and/or to 
• one or more of  five auxiliary destinations; the AUX1-5  outputs.

In a sort of technical short-hand, this mixer may referred to as a 22:4:2 mixer (with 5 auxiliaries) to indicate it offers 22 inputs, 4 group outputs, and 2 main outputs (with 5 auxiliaries).

Although the mixer may appear to be complicated, it is in fact, composed of only a few different building blocks, called modules  or strips.  Each type of strip groups together all the controls and internal circuitry to perform similar functions.

On this mixer, there are two kinds of  INPUT strips, 14 MONO and 6 STEREO.  The INPUT strips are grouped together on the left side of the mixer.  The  AUX/GROUP/MASTER strip is on the extreme right.

You will only need to learn the operation of these few strips, 

• MONO INPUT 
• STEREO INPUT  (3 variants)  
• AUX/GROUP/MASTER OUTPUT

in order to "master" (sorry) 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 GAIN control allows you to adjust the input strip so that you can operate with the white channel fader in its normal range, around -0- on the scale -- no amplification. This assures that the signal will have the maximum headroom and minimum noise.  (See PFL 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.

The GAIN control is the most important  setting on the console.  

• Set it correctly, you have the best possible chance of getting good sound. 
• Set it incorrectly, and nothing you do to the signal later in the audio path will fix it.

The 100Hz (High Pass --  Low Cut Filter) button allows you to remove unwanted low-frequency noise from the input signal.

• It cuts sharply (@18dB/octave) below 100Hz
• It can be used to cut traffic or air conditioning rumble
• Don't use this filter on bass guitars or tubas.

The USB RTN (Universal Serial Bus Return) allows you to choose between the analog channel input and the digital signal from a computer.

The LIMITER button will engage a simple automatic gain control on the channel.  The brightness of the LED indicates the amount of gain reduction being applied.

The LIMITER function is only availble on MONO Input Channels 1-8.

The HI-Z  button causes the LINE TRS jack to appear electrically similar to the input jack  on a guitar amplifier.  This can allow you to record an instrument like an electric guitar by connecting it directly to the console.

The HI-Z  function is only availble on MONO Input Channels 7-10.

The EQ (EQualiser) section of the input strip allows you to adjust the tonal qualities of the input signal.  The EQ is to sound, what coloured "gels" are to lighting.

 Shelving

• boost or cut 15dB @ 12kHz

• boost or cut 15dB
• variable  centre frequency from 400 Hz to  8.0  kHz

• boost or cut 15dB
• variable  centre frequency from 80 Hz to  2.0  kHz

LF: (Low Frequency)

 Shelving

• boost or cut 15dB @ 60Hz

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. 

The MUTE button cuts-off (mutes) the input signal from the selected outputs.

The PFL (Pre-Fade Listen) button sends the input signal directly to the left/right LED meters and the headphones.  A red LED (AFL/PFL ACTIVE), just below the meters indicates that at least one PFL button is pressed.

With PFL pressed on one input channel, 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- dB point.  They should never go higher than +6

Don't forget to release the PFL button afterwards! 

On the SIGNATURE 22 MTK, input channels 15/16,  17/18, 19/20 and 21/22 are STEREO input channels.

STEREO inputs are used for sources with a left and a right output -- CD or DVD players, keyboards, effects processors or computer audio outputs.  A single fader controls the level of both left and right  channels of the source.

STEREO channels 15/16 and 17/18 have a 3-pin XLR connector to accept the output of a microphone.  The  microphone signal is sent to both left and right inputs.  They have a pair (left/right) of TRS sockets to accept a left and right line level source.

STEREO channel 19/20 has no microphone level input, and the line level input is on a pair of TRS sockets.

Alternatively, the input could be from USB RTN channels 19/20.

STEREO channel 21/22 has no microphone level input, and the analog line level input is on a pair of RCA sockets.

Alternatively, the input could be from USB RTN channels 21/22.

On the SIGNATURE 22 MTK, what you might think would be input channels 23/24 and 25/26 get their signal from the internal effects processors, and are labelled FX RETURN 1 and 2.

Because the source is internal to the console, there are no input sockets.

Most of the other controls on a STEREO Input strip are identical to those on a  MONO Strip.  Two exceptions --

• the PAN control on a STEREO channel is called BAL (BALance) but serves the same function.
• the EQ on a stereo channel  is simpler, having only one parametric band, not two.
  

The AUX1-5 MST (MaSTer) controls set  the level of signals sent to the AUX1-5  SEND busses and to the AUX 1-5  TRS output connectors.

The  PRE/POST button allows AUX SEND to be sent either PRE or POST (fader).

The AFL (After Fader Listen)  button allows you to SOLO any of the AUX SEND busses.

.

The GROUP 1-2 faders set the level of signals sent to the GROUP 1  and GROUP 2 busses, and to the GRP1 and to the GRP2 TRS output connectors.

If you want to use the GROUP 1-2 faders as SUBGROUPS (or Sub Masters), pressing the corresponding MST button, will send the signals on to the Master buss.

The MONO button will cause the GROUP 1  and GROUP 2 buss signals to be mixed to mono before being fed to the Master bus.

The MASTER fader sets the level of signals sent to the Master  buss, and to the MST L and to the MST R XLR output connectors.

The INTERVAL MUTE  button will mute all input channels except STEREO Input channel 21/22.

The meters on the Signature 12MTK show Master Left/Right output level in normal operation.

If a SOLO (PFL or AFL) button is activated then the meters will display Solo bus levels.

When any SOLO button on the console is depressed, the "AFL/PFL" will light to indicate this condition.

Check this LED if the headphone/monitoring output is not as expected.

The headphone signal is always the Master Stereo Output unless a Solo (PFL or AFL) is activated.

In that case, the headphone output is switched to the Solo Bus.

This USB Type-A socket is for attaching a USB-powered LED lamp - NOT for recharging your phone.

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" LED indicates that 48 volt PHANTOM POWER has been applied to all of the microphone sockets by the "PHANTOM POWER" button.

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

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