Audio: What Are Mixer Inserts? (Mixing, Recording & More)

Inserts are important parts of mixers that are sometimes taken for granted in modern digital audio workstations. If you're unsure of what mixer inserts are or you want to gather more information on inserts and their importance in audio engineering, you've come to the right place!

In this article, we'll discuss inserts in more detail in both analog and digital audio systems and their importance in mixing, recording, mastering, and more.

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A Primer On Signal Flow

To understand inserts, we should first consider signal flow, particularly the signal flow of a mixer/DAW channel.

As the name would suggest, signal flow refers to the flow of an audio signal from its starting point to its ending point. In other words, how is the signal routed from one device or signal path to another?

More specifically, for the discussion of this article, how do audio signals flow through the channels of our mixers/DAWs?

A mixer/DAW channel/track will have an input. This is true of audio tracks, aux tracks (including returns, subgroups, and alternative mix tracks), and even MIDI tracks (often set as a virtual instrument).

In hardware mixers, there will usually be a preamp immediately after the input to apply gain to the signal.

Depending on the mixer, we may also find some built-in effects in the channel strip. Semi-parametric EQ is by far the most common process we'll find on mixer channels.

Whether there are built-in processes or not, the next step is typically the insert section. Left alone, the insert section will pass audio as if it wasn't in the signal path whatsoever. However, inserts will prove invaluable for adding effects and processing, as we'll see shortly.

Beyond the inserts, we'll have auxiliary send options, which we can use to send audio from the channel to auxiliary tracks independently of the output. These sends can be set as pre- or post-fader.

After the sends, we have the panning pot and the fader, which control the directional position of the track's audio in the panorama and the output level of the track, respectively.

Finally, we have the channel output, which routes the signal via a bus to wherever it has to go next. By default, tracks are typically outputted to the mix bus or main mix outputs. However, we can often change the output to a subgroup if we prefer mixing that way.

For more info on using bussing in your mixes, check out my YouTube video here:

With that quick primer on channel signal flow, let's move on to inserts more specifically.

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What Are Mixer Inserts?

While signal flow is still fresh in our minds, let's understand the basic flow of an insert.

An insert of a mixer channel starts with an output. The signal audio can be outputted from the channel and inputted into a processor or effect (or multiple in-line). The insert of a channel ends with an input, where the audio from the processor or effect (or multiple) will come back into the channel at the same point, continuing through the channel.

Inserts are not aux sends, which allow for parallel processing. Rather, they allow processors/effects to be inserted directly in-line.

In analog systems, inserts are physically patched from the channel to hardware processors/effects units and then patched back into the channel. In digital systems, this patching is done virtually, and it's easy to insert plugins across our channels as we see fit.

As you can imagine, inserting a hardware unit is a bit more limiting than using plugins.

First, hardware units are expensive, especially when we want multiples across many different channels. Beyond potential CPU load issues and latency, plugins can be duplicated far more easily.

Second, we would have to physically patch hardware into a mixer and dial it in for the mix, only to have to use it for something else in another mix. Recall is a pain in these situations. Plugins, on the other hand, offer complete recall as their settings are saved with our DAW sessions.

But whether we're using analog hardware or working completely in-the-box, the concept of inserts remains the same. Processes and effects can be inserted in-line between the channel input/preamp and its sends/pan/fader/output.

I'll reiterate that inserts are pre-fader rather than post-fader. There's a big distinction here, and it's a big reason why gain staging our tracks is so important.

I have a video dedicated to gain staging. Check it out here:

Note that inserts aren't only for audio tracks, either. They can be inserted on auxiliary tracks as well, including subgroups, the main mix (mix bus channel), effects returns, submixes, and more.

We'll often use inserts during the mixing process to get the best balance possible between all our tracks (in level and space). However, we can also run our audio through inserts during the recording process and “print” the effects/processing to the recorded audio if we so desire.

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A Brief Discussion On Commonly-Inserted Processes & Effects

Now that we understand the concept of inserts and how they work from a signal flow perspective, let's consider a few of the most commonly inserted effects and processes. In this section, we'll discuss the following:

• EQ
• Compression
• Saturation
• Delay
• Reverb

EQ

As mentioned, some mixers have built-in channel equalization. Even so, EQ is one of the most commonly used processors in audio production.

Equalization (EQ) is the process of adjusting the relative level balance between frequencies within an audio signal. This process increases or decreases the relative amplitudes of some frequency bands compared to other bands with filters, gain boosts and gain cuts.

EQ is a mixing tool for fixing imbalances in frequencies. It's often used to shape the frequency content of individual tracks, subgroups and effects returns and parallel channels.

Compression

Compression is a dynamics processor, meaning it processes the dynamic range of a signal. More specifically, it reduces or “compresses” the dynamic range of the signal running through it.

Dynamic range is the difference between the “loudest part” (the highest signal level) of a signal and the “quietest part” (the lowest signal level) of an audio signal.

Compressors accomplish this dynamic range reduction by reducing the output level once the input level surpasses a certain threshold. When the input signal is above the threshold, the output signal will be reduced according to a set ratio. However, the compressor will not reduce the signal when the input level is below the set threshold.

Compression is common for shaping the dynamics of individual tracks and subgroups; it's a popular process for parallel processing, it's popular on the main mix/mix bus, and it can help shape effects return channels as well.

Saturation

Saturation is an audio effect fusing soft-knee/program-dependent compression with harmonic generation/distortion. It produces new harmonics and enhances pre-existing harmonics in a signal in a sonically pleasing way.

Saturation occurs naturally due to the nonlinearity of analog equipment (even if only slightly), particularly in tubes, tape, transformers and transistors. It is also achievable digitally with plugins.

Saturation is a great tool that can be inserted on any and all channels if the mix calls for it. Of course, we may not need additional saturation if we're using analog gear. However, for purely in-the-box work, saturation can really add warmth and punch to the mix.

Delay

Delay, as an audio effect, is the process of recording an input signal to a storage medium and playing it back (often along with the original signal) after a period of time.

Depending on the delay effect unit and its settings, the processed/delayed signal can be played back once or multiple times. The delayed signal level can often be adjusted relative to the original dry signal. It may also be fed back into the delay processing circuit to produce further delay.

The best way to incorporate delay into our mixes is to set up an auxiliary track effects return and insert the delay on the return channel. That way, we have full fader and panning control over the delayed signal without affecting the original tracks sending to the effect return. We can also insert other processes/effects to enhance the delay without, again, affecting the original audio.

Reverb

Reverb, as an audio effect, is designed to emulate real-world reverberation.

Reverberation happens due to the natural reflections of sound waves in physical acoustic spaces. As sound travels from a source, it reflects off different surfaces at varying times before reaching the listener (after the direct sound reaches the listener).

All of these reflections blend together to form a single, continuous sound. If we separate this “single, continuous sound” from the direct sound, we have reverberation.

Like delay, the best way to incorporate reverb into our mixes is to set up an auxiliary track effects return and insert the reverb on the return channel. That way, we have full fader and panning control over the reverb without affecting the original tracks sending to the effect return. We can also insert other processes/effects to enhance the reverb without affecting the original audio.

I discuss how to use effects sends/returns and the benefits of doing so in the following YouTube video: