Sound Advice: Auxiliary Mixes

CR1604 Aux Sends

In this article, we will continue examining the audio flow through a typical audio mixer.  In previous articles, we covered the path audio takes as it enters the mixer via the channel inputs, such as a microphone connected to one of the mixer’s channel inputs, and how to control its volume by using the channel fader, and then controlling the master volume of all our channels via the master fader, where it is then sent to the main outputs of the audio mixer.  This main output would be considered our main mix and would typically be sent to the loudspeakers that project to the main audience.  So, we now can adjust the volume of all inputs individually, using the channel faders for each input, as well as the volume of our main speakers using the master fader.

In some situations, the main mix is the only mix needed from the audio mixer, since you may only have a couple of main loudspeakers connected to the audio mixer that serve the audience.  But, in most live performance setups, additional mixes are needed to feed additional loudspeakers.  Examples would be monitor loudspeakers that sit on the stage to serve the singers, monitor loudspeakers that serve the musicians, monitor loudspeakers that serve the choir or an ensemble, and the list goes on.  Interestingly, each one of these groups of loudspeakers will probably need to have its own mix which would be mixed differently than the main loudspeakers.  So, how can we create a completely different mix for the stage monitors or the choir monitors since the audio mixer has only one fader to control its volume?  Let me introduce you to the auxiliary mixes.

Most audio mixers have what’s known as auxiliary mixes.  They are sometimes simply called auxes or mixes, depending on the mixer.  Smaller mixers may have only one or two, whereas larger analog mixers may have eight or more.  Digital mixers can have anywhere from just a few to more than sixteen!   In continuing with the theme of our original mix assignment (from previous articles), we are going to use an auxiliary mix to feed a pair of stage monitors.  This mix will be completely independent of the main mix that is going to our primary loudspeakers for the audience.

Setting Up A Basic Monitor Mix

In the photo above, the volume controls for each auxiliary mix found on each channel are shown.  This mixer is the classic Mackie CR1604 16 channel mixer, but it is very typical of small to medium analog audio mixers typically used in small to medium churches.  You can see that this particular mixer has labeled them AUX, which represents your auxiliary mixes.

We are going to use auxiliary mix one (1) as our stage monitor mix.  But, before we get into turning and adjusting the controls, we need to connect the output of auxiliary mix one to our monitor loudspeakers.  This is accomplished by finding the auxiliary mix one output jack on the rear or back of the audio mixer.  This output can be referred to as an AUX SEND, as seen in the photo to the left.  You can see that there are six of these output jacks, numbered one through six.  Onyx 1640i AuxJacksThey correspond to our six auxiliary mixes that we can configure and control on the audio mixer.  But, we are only interested in send one.  And, disregard the returns, for now.  We’ll talk about returns later.

Now, with our monitors successfully hooked up to the AUX SEND 1 output jack, we are ready to begin creating our monitor mix.  In addition to AUX controls on each channel, your audio mixer will have master auxiliary volume controls in the master section of the mixer, probably near the master fader.  There should be a master volume control for each auxiliary mix, so, in this example, this audio mixer would have six auxiliary master volume controls.  Let’s find the master volume for auxiliary mix one, and on this mixer I believe it is labeled AUX 1 MASTER.  Let’s turn that control to the 12 o’clock position, which would place it midway in its rotation, pointing northward.

Next, we need to make sure our auxiliary mix control on each channel is set to PRE, which stands for pre-fader.  This means that our audio signal that we are controlling for this particular auxiliary mix is being tapped before it gets to the fader.  Why does this matter?  Well, if the PRE switch is not pressed, then our audio signal will be retrieved post-fader, or after it goes through the channel fader.  So, in that scenario, our channel fader’s position controls how much audio is available to control via the AUX 1 volume control on that particular channel and ultimately send to the AUX 1 MASTER control.  During post-fader operation, if the channel fader is all the way down, or turned off, then you will have no audio signal present for your auxiliary mix.  We’ll discuss post-fader some more in a moment.

Now, on each individual channel we can control how much of that channel’s audio we want to “send” to that auxiliary mix by adjusting the AUX 1 control on that particular channel.  For example:  If we just want piano in the stage monitor speakers, we would turn up the AUX 1 volume control on the channel where the piano is connected.  That would send a certain portion of the piano’s audio signal to the AUX 1 MASTER volume control, where it is then sent out the AUX SEND 1 output jack on the rear of the mixer.  If you also want some acoustic guitar in the stage monitors, you can adjust the AUX 1 volume control on the channel that belongs to the acoustic guitar.  Now, you can control the volume level of each instrument, microphone, etc. using the AUX 1 controls on each channel.  Adjust the overall stage monitor volume with the AUX 1 MASTER volume control.  It’s really that easy!

If you have another stage monitor, such as beside the piano, where you want to create a separate mix, you could repeat this entire process using AUX 2.  In that case, AUX 2 would be an auxiliary mix just for the piano monitor, and AUX 1 would be the auxiliary mix dedicated to the stage monitor.  You can repeat this idea for as many monitor mixes that you need, assuming you have enough auxiliary outputs on your mixer.  What you will quickly realize is what most sound technicians learn very quickly:  There never seems to be enough auxiliary mixes on the audio mixer!

Pre-fader vs. Post-fader

In our previous example, our auxiliary mix that we created to send to the stage monitors is completely independent of our main mix, and in many cases, is the best idea.  What I mean by “independent” is the auxiliary mix will not be affected by adjusting the channel faders for the main mix.  But, there could be situations where this is either undesirable or ineffective.

The ability to change the auxiliary mix’s audio source path is a feature that most modern audio mixers provide.  When an auxiliary mix gets its audio pre-fader, that means the audio at the auxiliary control on that channel is sourced, or tapped, before it even gets to the channel fader.  This means that the amount, or volume, of the audio available for your auxiliary  control is constant and can’t be altered, either accidentally or intentionally, using the channel fader.  So, once you get your stage monitor mix set exactly like the singers want, now you can begin to adjust the channel faders for the house mix and not affect their monitor mix!

When an auxiliary is set to post-fader, the audio available to the auxiliary control is sourced after it has gone through the channel’s fader.  This means that the channel fader will increase and decrease the audio going out through that particular auxiliary mix, depending on the channel fader’s position.  If the channel fader is all the way down, or off, then you will not get any of that channel’s audio out through the auxiliary.  This can be confusing for the new sound technician, so some practice and awareness is usually needed to prevent getting in a pinch with post-fader aux mixes.

So, why do many audio mixers have both, or allow you to select either pre-fader or post-fader?  Let’s look at a few scenarios where this can be important…

  • Music playback – If you have your stage monitors on an auxiliary mix that is pre-fader, and you want your prerecorded music to be in the monitors, then you will run into a slight “issue” when playing music from your CD player or computer primarily intended for the audience.  Most of the time, you will want the ability to fade the music out when needed.  And, when you do, you will notice the music is still playing in the monitors!  To prevent this from happening AND still have the music in the monitors, make sure that the auxiliary for the stage monitors is set to post-fader on the channel(s) for the pre-recorded music.  Try it!
  • Performance split soundtracks – Many churches use performance soundtracks, or split-tracks, for their choir performances.  Split-tracks are specially created soundtracks that take advantage of stereo’s two tracks of audio, known as left and right, by placing all the music on one side, such as the left, and the background or guide vocals on the right side.  These are played back traditionally from a CD player, but today I would suppose most churches have moved to using a computer.  But, in either case, two channels are used on the audio mixer:  one for the left (music) and one for the right (vocals).  Since you probably don’t want the guide vocals in the main mix and only in the monitors for the choir or performers, you will have the fader all the way down, or off, and the auxiliary mix on that channel set to pre-fader, so the fader’s position doesn’t affect the monitor mix.
  • Praise team vocals – For many channels on the audio mixer, whether you use pre-fader or post-fader can simply boil down to personal preference.  And, sometimes this setting can change within a service depending on the need.  This can include instruments, vocals, the pastor, etc.  But, I generally prefer, and recommend, to have the praise team vocalists set to post-fader when using stage floor monitors.  This can generally help prevent unwanted feedback problems by keeping the mic’s turned down in the monitors when you turn them down in the main mix.  Post-fader also will usually mute that channel in the auxiliary when you mute it in the main mix (This does vary with different audio mixers, so consult the owner’s manual for details on your mixer).
  • In-ear monitors – If you are using auxiliary mixes to feed in-ear monitor systems, you probably want those auxiliaries to operate pre-fader.  There are some exceptions, but since the audience can’t hear the in-ear mix, and feedback is not an issue, then pre-fader is usually the way to go…and it will be less distracting to their mix, as well, by not being affected by any channel fader changes.
  • Reverb & Effects – Most of the time, auxiliaries that are used for effects will be used in a post-fader configuration.  There are some exceptions, but this would be the default configuration.  So, if AUX 4 is your reverb or effects processor mix, then make sure this auxiliary mix is simply set to post-fader on every channel (more info below).
  • Lobby or Nursery speakers – Many churches use an available auxiliary on the audio mixer to create a mix for the lobby speakers or the nursery.  Since you will probably want this mix to be very close to the main house mix, then simply configure this auxiliary as post-fader on every channel, AND set the aux level on each channel identical.  This will create an aux mix that closely resembles the main mix.  You can obviously then adjust individual channels, where you might need a little more or less of something particular in those locations.

TIP:  Pre- and Post-fader options differ from one audio mixer to another, so it’s important to read the owner’s manual to your particular mixer for the specifics on how this is implemented and works with your equipment.

Auxiliary Gain Structure

Now that you have setup some auxiliary mixes, it’s worth mentioning that proper gain structure is very important with your auxiliary mixes.  Simply stated, you don’t want to overload or distort your master auxiliary volume control by sending too much audio from each channel.  The proper method for setting this gain structure differs slightly depending on the audio mixer, but can generally be gauged by simply viewing the position of your auxiliary controls.  If your individual channel auxiliary controls are set family high, but the auxiliary master control is very low, you probably have a major problem with overdriving the auxiliary master.  Likewise, if you individual controls are very low, but the master control is very high, you probably don’t have quite enough audio from each channel going to the auxiliary.  There probably should be some consistency across these controls, but there are no specific rules.  And, without trying to sound contradictory, you shouldn’t be setting an audio mixer’s controls primarily by sight, anyway.  Use your ears and some common sense best practices.

TIP:  If your audio mixer allows you to monitor auxiliary audio levels using the main level meter, much like you do with the main mix gain structure, then, by all means, use it.  It could be a hidden feature using the pre-fade listen (PFL) button.  Check your owner’s manual for details.

Reverb & Effects

Another important use of auxiliary mixes is reverb and effects.  Whether you have an external reverb or effects processor that must be interfaced to your audio mixer, or whether you have a built-in effects processor, they are usually operated through the use of auxiliary mixes.  Let’s use a simple reverb processor as an example.

A typical reverb or effects processor will have an input (mono or stereo) and a stereo output (usually stereo only, but could have a mono option).  Usually, you connect the processor’s input to the output of one of your auxiliary outputs, such as AUX 4.  Don’t forget that a post-fader auxiliary mix should be used, so, depending on the audio mixer, that could determine which auxiliaries that you can use.

The output of the processor would be connected into the AUX 4 RETURN, since we are now wanting the processed audio with reverb or effects to be returned back to the mixer.  Now, the returned audio can be mixed in with the main mix or a stage monitor mix, depending on the capabilities of the audio mixer.

Using the individual auxiliary controls on each channel, you can determine which audio signals are sent to the effects processor.  Now, to increase the amount of reverb on the lead singer, you can simply turn up that auxiliary control on the lead singer’s channel.

TIP:  Many sound technicians choose to route the processor’s output into an available channel on the audio mixer instead of using the auxiliary return.  There are advantages and disadvantages to this, but it does give you better control over the processed signal and the ability to tweak the processed audio using channel EQ as it comes back from the processor.  Most of the low end to mid-range audio mixers do not have EQ controls on the auxiliary returns.  This is an easy way around that limitation, assuming your mixer has an available channel.  

NoNo’s:  Be sure to NEVER send audio back to the same auxiliary from where it just came from.  In other words, you wouldn’t send AUX 4 RETURN back to AUX 4.  This would cause an internal feedback loop that would be loud and nasty!  This is also especially true when you use a channel for the processor’s return audio.

Pre & Post EQ

Another option that some audio mixers have is the ability to switch some, or all, auxiliary mixes to pre- or post-EQ.  This is very similar to pre- or post-fader.  If the auxiliary is set to pre-EQ, then the auxiliary audio from that channel will not be affected by the channel EQ.  Likewise, if the auxiliary is post-EQ, then the audio sent out through the auxiliary for that channel will be affected by the EQ.  On audio mixers where this is not apparently selectable, it may still exist.  Your pre-fader option may also be pre-EQ, and your post-fader option will also be post-EQ.  Again, you need to consult your audio mixer’s owner’s manual for the specifics.

So, when do I use pre and post?  A pre-EQ auxiliary is great for in-ear monitor mixes, where you don’t want the EQ you’ve adjusted to fit with the main mix to affect the audio sent to the musician’s in-ear mix.  But, if you do, then simply use a post-EQ auxiliary mix.

TIP:  Some audio mixer’s have auxiliaries that are internally configurable for pre- and post-EQ using jumper settings.  The Mackie 1604 is a good example.  I’m sure other mixers offer similar configurations.  So, just because you don’t see a button or switch where you can change pre or post, there still may be hope.  Consult the service manual for the audio mixer (usually found on the internet), or check with Google!

Final Thoughts

Auxiliary mixes are very handy and versatile features found on almost every audio mixer made today, and this article has only summarized auxiliary usage.  With the new round of digital consoles popular in the market today, you likely have more auxiliary mixes than ever before available on small to medium audio mixers.  And, that’s a good thing, especially if you need several mixes for the musicians’ in-ear monitors.  You also have auxiliaries to use for multiple effects processors, in-ear mixes, foyers, recorders, and much more.  And, as you can see from this article, there are lots of flexibility with using them.  Spend some time researching what you need a particular auxiliary mix to do, and then try it.  In most cases, it’s not difficult to change if your current configuration doesn’t meet your need.

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