This post removes the confusion about pre-fader, post-fader, aux sends/return and Insert FX in audio mixing and recording. Whether you are mixing entirely using a software or a hardware mixing console; this guide will be applicable. First, you might have encountered these terms in your audio mixing software or mixing boards/console. And then you are confused how you are going to use it.
Before digging further, you need to learn the basic “signal path” of audio in the mixer. This signal path is the same regardless you are using a software or not. In some DAW software they even add more connectivity in terms of aux send/returns and inserts, but the overall principle stays the same. After you throughly learn the concept, it is just a matter of looking into the audio mixing/recording software manuals or mixing console manuals where to find these things.
Signal path in an audio mixer
Look at the signal path diagram below illustrating only a single channel strip in a mixer (actual mixer can have several channels, for example a 24 channel mixer so there are 24 strips) :
signal path in an audio mixer
The signal paths are shown in dark gray arrows. Pre-fader means BEFORE the Fader knob and Post-fader implies AFTER the Fader knob. The Fader knob is simply a volume knob in that specific channel. This is usually a big white knob/slider like the one below:
fader knob
photo credits: Michael Sarver
You should find one similar to that in your audio mixing software or hardware. There is a lot of uses for Aux send and return. They are used in connecting parallel audio devices such as outboard effects. Hence it is called parallel effects.
There are pre-fader aux/sends that allows you to add parallel effects before sending the signal to the fader. Or you can also use the post-fader aux send/return. There is also “Insert FX” where the signal path is “serial” instead of parallel. As you can see in the signal path diagram above, the “Insert FX” is connected in series with the rest of the path. Most mixing console or board whether digital or analog has InsertFX before fader.
The most common FX hardware that is connected in series to the signal path (also called “Insert FX”) are the EQ and compressors.
Using Parallel or Serial Effects in the mixer
One common question: “When to use parallel or serial based audio effects/processors?”
If you connect the effects in parallel, you have two kinds of signals: the “Dry” and the “Wet”. Dry is the original, unaltered audio signal while the wet is altered signal by the effects. So you can basically adjust the Dry/Wet ratio with parallel effects. Connecting effects in parallel results to having two signals combined signal (dry and wet). The amount of wet signal depends on the setting of the FX hardware connected in parallel.
A common example if the reverb (which is a parallel effect) has settings of 40%dry and 60% wet. Technically; the aux sends dry and then the aux return has some reverb signal which is around 60% mixed. Use parallel effects if you like to control a dry/wet signal response. Insert FX effects need to have one input and one output. The output is a direct function of the effect settings except if you bypass it.
In music production, the most popular application of connecting FX in parallel are the following:
a.) Using Reverb
b.) Implementing parallel compression to make bigger and powerful sounds of drum or other instruments.
Which one to use? Pre-fader or Post-fader
Another common question: “Which is better to use, Post Fader or Pre-fader Aux Sends/Returns?” It depends on your audio application. For example pre-fader is useful in situation where you would like to pre-monitor the output without yet adjusting the fader. Let’s elaborate. This is how the signal path when connecting in pre-fader:
Signal —- > FX in Pre-fader —- > Fader
Now if you send the output of the pre-fader to any monitoring equipments (your headphone for example), then you will only hear the outputs of the FX connected in pre-fader. If you increase the fader volume up or down, the output of the pre-fader is unchanged because it will not be affected by changes with the fader. The primary reason is that its output is not passing the fader. This is useful if you like to listen how the mix would sound like without adjusting the fader.
In post-fader connection, one of the most popular effects will be the reverb. This is connected in post-fader to correctly maintain the dry/wet ratio with corresponding changes in volume level. For details on this topic, please read this tutorial on how to use a reverb unit.
Looking back on the first screenshot on this article, you will only see one channel strip of an audio mixer. Real mixers have more than one channel strips (typically 8 or even 24-channels depending on the size of your mixer). All you need is to remember how one channel strip works in the mixer. Then you will know how you will be using the pre-fader and post-fader connections in your projects. Once you know this, everything else will be very easy and you can see the same channel strips throughout your mixing hardware.
Take note that the input audio to the channel strip is either coming from a microphone pre-amp. While the output audio is the resulting processed audio of all effects combined (sends or inserts).
This output can then be panned depending on its location in the stereo field. Finally if you are mixing 2 or more tracks (channels), the summation of each processed audio output from each channel will become the output to the main mix monitor (the main mixer output). Think of it like this:
Processed audio output (Channel 1 + Channel 2 + Channel X…) = Stereo Signal at Main Mix Monitor
Content last updated on June 28, 2012