Sound Advice: Channel Faders and the Main Outputs

In the previous article, you received your first mixing assignment using just a microphone and an audio mixer.  We discussed the proper techniques for getting audio into your audio mixer’s channels and properly setting the channel input gain.  Now that we have the correct amount of audio in the channel strip, let’s discuss where the audio goes once it leaves the channel strip, headed to the output section of the mixer.

Looking at a typical channel strip as shown in the figure on the right, the audio that we properly adjusted coming into the strip via the gain, or trim, setting now visually flows through the channel strip from the top to the bottom, eventually arriving at the channel fader.  During the audio’s journey through the channel strip, there are usually options for sending it to auxiliary outputs, as well as options for altering the way the audio sounds, which we will cover later.  But, for now, we are going to simply focus on the channel fader control and it’s function in sending the channel’s audio to the audio mixer’s various outputs.

The audio mixer that is shown in the figure on the right represents a typical, small audio mixer commonly used in churches, as well as schools, bands, and recording setups for musicians.  This audio mixer also has a main output capable of both mono and stereo applications.  The main output has two master faders, one for the left output and one for right output (for stereo applications), that is used to control the master volume of the mixer, as shown below.  When the mono output is used instead of the separate right and left outputs, then both faders can be used and treated as a single fader.  Some audio mixers have an additional, separate master fader for the mono output.  If that is the case, then the mono fader should be used and ignore the separate left and right faders.  Consult the manual for your particular audio mixer for help.

NOTE:  Mono is the choice for most church and band sound systems, where both (or all) of the main speakers reproduce the exact same audio signal.  In a stereo setup, you could have different audio signals in the left speaker versus the right speaker.  Stereo setups are more complex, harder to mix properly, more costly, and many times do not work well with the layout and/or the acoustics of the typical church, causing the audience to miss out on some of the intended audio.  So, for that reason, most church sound systems are mono.  And, there’s nothing wrong with mono configurations.  We’ll tackle mono versus stereo, plus another format, in a later article.

 

Now, looking back at our channel strip to the right of the channel fader, we see three switches labeled 1-2, 3-4, and L-R (we will cover the SOLO switch later).  These switches assign, or route, the audio from this particular channel to its destination.  So, to get this channel’s audio to the main output master fader, we need to press the L-R switch.  Now, this channel’s audio is routed to the main stereo output, as well as the mono output (which is one and the same).  Moving the channel fader up and down will now control how much of this channel’s audio is sent to the main output’s master fader.

Proper Fader Techniques

Properly setting the faders on an audio mixer that controls only one microphone through one channel that’s routed to the main output is a rather simple and straightforward task.  Both the channel fader and the master fader would be set at, or around, 0 dB, for normal operation and you would be good to go.  But, when your mix begins to involve several channels all going to the master fader, some simple and logical principles need to be implemented.

Let’s start with the master fader.  In a live setting, it’s important to calibrate your entire system so that your audio mixer’s main output meter reflects a meaningful value that can be easily referenced.  As an example, let’s say that your church likes the average loudness, as measured with an SPL meter, to be around 85 dB during a typical worship service.  Then, your audio mixer’s meter needs to accurately read 0 dB when the average SPL is at 85 dB.  So, 0 dB on the audio mixer would now indicate that you are at the ideal SPL for your environment.  Now, with a properly setup and calibrated meter on your mixer, you don’t need an SPL meter.  The main output meter on the audio mixer, and your ears, should tell you almost everything you need to know.

TIP:  Properly setting up and calibrating the audio mixer’s main, or master, audio level meter is accomplished by the proper gain setup of your main amplifiers, loudspeakers, and loudspeaker processors, if any.  This all has to do with proper gain staging throughout the entire audio system and will be discussed in an article in the near future.  For now, know that if your sound system loudness, or volume, gets too loud before you meter even gets close to 0 dB, then turn your amplifier’s gain back.  If you are using powered speakers, turn their gains down, instead.  This will allow your audio mixer to output more audio and read properly on its meter.

As the number of channels you begin to send to the master fader increase, the overall volume of each channel must be reduced to prevent overloading the master fader.  In other words, the faders on all 16 channels will probably not be set at 0 dB, but at values closer to -10 or below, depending on the channels’ audio signals.  The main output meter of many audio mixers can display the level of audio before the master fader, correctly letting you know if you are overloading the master fader.  Consult the manual to your particular meter if you are unsure.  The master fader simply controls the master volume headed to your loudspeakers.  It’s position is not critical, as long as your system is properly calibrated as described earlier in this article.

If your master fader is not correctly calibrated, then it’s very possible that, during a normal worship service or show, your master fader will be set either too low or too high.  This creates a situation that can compromise the performance of your audio system, introducing unnecessary noise and/or distortion that may or may not be immediately apparent to you.  Again, as stated before, your master fader would ideally be around 0 dB during a service that is yielding an SPL in the venue of around 85 dB SPL (or whatever your ideal SPL would be).

No-No’s:   When I look at the positions of an audio mixer’s faders, such as the CR1604 in our example during normal use, most faders should be around their midrange position.  A few channels may be set lower while a couple may be higher than midrange.  Also, since a typical worship service is very dynamic with things changing, many faders will obviously be changing position during a service, so my statements are obviously generalities.  If all of your channel faders are set high and the master fader is very low, then you probably have the audio mixer set improperly.  This scenario may be overdriving, or overloading, your master fader.  Similarly, if all the channel faders are set very low and the master fader is at 0 dB or higher, there are also gain issues somewhere that need to be addressed.  Here, you are using your master fader to make up gain that you are not properly getting from the individual channels, possibly introducing noise or negatively affecting the quality of your audio.  Review your individual channel gain/trim settings and your master meter calibration.

Conclusion

We are well under way into our first mixing assignment, even adding additional channels to the mix, and this article helps you ensure that your gain structure throughout the audio mixer is properly setup.  In the next article, we will revisit the channel strip and get into understanding the auxiliary busses and how to properly use them for creating a monitor mix or for adding effects, such as reverb, to the channel’s audio signal.

Coming up very soon will be some articles detailing specific mix examples, hints, and techniques, featuring sound clips and, possibly, even videos.  Be sure to spread the word and feel free to leave a comment on how these articles have helped you.