Mixing Board Breakdown: Part III - Split Consoles, Routing and More

This is a continuation of an earlier article. You can check out earlier segments below:

Part I: Introduction and Basics

Part II: The Input Stage

Auxiliary Sends

Moving on to the next important piece on a mixing board, the number of auxiliary outputs highly depends on the intended use of a mixing console, although the normal range is somewhere between one and eight. These auxiliary sends are able to be switched in order to derive their signals from either before or after it hits the channel fader. This option is included so that the output signal level will either be dependent or independent upon the position of the fader. When it comes to the pre-fader auxiliary send, it is usually taken from a point after it hits the equalizer, although there are some boards that give the option to take it from a point before the EQ.

Like many other things in life, there are both pros and cons to either option, depending on what you’re intended uses for the pre-fade sends are for. As a small example, a pre-EQ feed might work better for foldback purposes so that adjusting the EQ doesn’t cause any unwanted feedback, while using post-EQ feeds would work better for effects or headphone cue signals. Pre-fader sends are usually used for foldback or cue signals so that opening and closing those specific channel faders won’t affect the performer’s ability to monitor their piece. Post-fader sends are generally used more for house PA systems in broadcast and theatrical situations in order for the audience to only hear sources when they are faded up. Post-fader sends are also regularly used for most types of signal processing, particularly with artificial reverb.

Using post-fader auxiliary sends is extremely important if a single effects processor is handling the contributions from a number of channels. When a channel fader is closed, its direct contribution to the output is removed along with its send to the effects unit. On the other hand, if a pre-fader is used, the channel will still be contributing to the effects-send even if the channel fader is closed, therefore it will continue to be heard through the effects-return (although that’s rarely a wanted outcome).

In order to minimize the number of unnecessary buttons, many mixers automatically select pre or post-fader status for pairs of auxiliary sends, so a little bit of tinkering might be required to optimize the use of auxiliaries for a certain situation. Larger boards might also allow one or more stereo auxiliary sends, usually using a pair of mono auxiliary busses where one send control becomes the stereo send level knob and the other becomes a pan-pot.



An output signal from one channel must be combined with that from other channels. In barebone mixers, all channels are sometimes permanently routed to a master stereo output, but usually channels are routed through groups and from there to the main outputs. Depending on the intended use of the mixer, there can be anything from two to 48 groups along with varying amounts of sophistication in terms of additional equalizers and auxiliary sends. Generally, the groups are assigned in pairs, with the channel pan-pot providing a way of restricting a signal to a single group as well as image positioning within a pair of groups for stereo working.

When you find yourself working in stereo, it is always better to use a dedicated stereo channel for a stereo signal source instead of a pair of mono channels panned left and right; channel gains, fader positions and EQ settings must be matched between the two sides of a stereo signal which is tough to do with separate channels (but a cinch when using a dedicated stereo channel).

One last thing while we’re on routing: unused channels should never be left routed to groups or main outputs simply because this usually degrades the noise performance of the mixing stages, although how likely this will occur depends on the specific details of the circuit topology used in the console.



Most commercial, general-use mixing boards are designed with very simple and easy to comprehend designs where the input channels are routed to a small number of groups, and from there to the main outputs. On the other hand, even with simplicity in mind, the structure of a mixer becomes a bit complicated if the board is meant to work in conjunction with a multi-track recorder, especially if a good amount of tracks are involved. In the case of multi-track mixers, the general school of thought is to feed each track from its own group, meaning that 24, 32 or even 48 groups might be necessary. This is done in order to allow multiple channels to feed a single track, such as for bounce-downs or what have you.

Although this isn’t a problem from a technical perspective, it does make for a rather large board, especially when adding a means of monitoring the tracks. Usually, this added means of monitoring is another complete mixer, so the structure of the entire thing becomes: Input Channels > Groups > Track Monitor Channels > Stereo Output. Just try and imagine a complete configuration with 72 inputs, 48 groups and 48 monitors – all side by side! It might look extremely impressive, but it’s far from practical. The name for this type of setup goes by the generic name split console, due to the fact that the recording input and monitoring functions of the setup are entirely separate. While it’s not that difficult to understand this setup, this approach can quickly become unmanageable as the number of tracks increases, making performing otherwise simple tasks such as bounce-downs require external signal patching in order to re-route monitor returns though input channels and then onto the group sends – a little confusing, right?

In order to counteract the impracticalities of the general split console, the In-Line arrangement was developed – which first became popular with the introduction of the original SSL 4000-Series mixers. Although it may sound like a complicated concept at first, it offers far more flexibility and requires much less physical space. In an In-Line mixing board, the channel sections become Input-Output (I/O) modules since each strip essentially incorporates all the functions of the channel inputs, group outputs and monitor returns associated to the pertinent strip number.

To put that in better context, imagine a certain component – let’s say for channel 6 – contains the microphone and line inputs for that channel, along with its auxiliary send controls and equalizer, fader (usually of the short-throw variety) and output routing. It also incorporates the mixing amplifier and output fader for group 6, which is normally tied directly to track 6. The monitor facilities will also be on this component and equipped with auxiliary sends, an equalizer and a monitor fader (usually of the long-through variety). Essentially, by combining all the features of a generic split console on one desk, In-Line boards allow even home-studio engineers the benefits of having all these several systems and functions by not only reducing their overall cost, but by reducing their size as well – not to mention getting rid of excess, unneeded knobs and buttons.

You would think that with a configuration aimed at streamlining the split console process that the ease of use would benefit as well. Unfortunately, packing in multiple functions on one board makes it very easy to become hopelessly confused about the signal path of a particular sound source unless you pay very close attention to labeling and use a bit of logical deduction from time to time. Try to imagine a situation where a microphone is plugged in to channel 6. It will be controlled by the input section and channel fader (usually small) in strip 6, then routed to track 17 so that the group trim control will be on strip 17 – and with the monitor return signal controlled by its own, larger fader. This signal path might not sound so convoluted at this point, but the likelihood loosing grasp of the situation grows as more things are brought into the mix, such as realizing that equalization is now available to both the recording channel and replay monitor sections of the board, along with the auxiliary sends. And trust me – its extremely easy to accidentally set up multiple effects of cue sends on the same signal but from different I/O modules. 

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