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Routing Audio Signals to Effects for Optimal Sound
Written by Michael Cooper - 2005, PRIMEDIA Business Magazines & Media Inc. Reprinted with Permission.
Whether you record and mix with hardware consoles or operate in the virtual world of the digital audio workstation (DAW), you need to know the various ways to route signals to effects processors in order to get optimal sound from your equipment. In this article, I will explain the advantages of using channel, subgroup, and master bus inserts; channel and subgroup aux sends; and master outputs for signal processing. I will also explore the reasons why using one signal route instead of another will yield superior results in specific applications. Advanced applications involving the use of mults, by which signals are split into two or more paths for separate processing, will also be discussed.

For simplicity's sake, I will address each topic from the perspective of hardware consoles, because DAW-based virtual mixers tend to emulate the routing capabilities of their real-world counterparts. However, CPU-processing limits occasionally require alternative methods of doing things on a DAW, and I will focus on those when appropriate.

All Or Nothing
I'll begin by discussing ways to process individual channels rather than an entire mix. The first output you're likely to encounter in a mixer's audio path, the channel insert, provides one of the best ways to process audio. When you patch a signal processor to a channel insert, 100 percent of that channel's signal flows out of the insert's send connector, through the signal processor, and back into the same mixer channel via the insert return. For that reason, it is best to use a channel insert when you want to process the entire signal, not just a portion of it.

Equalizers, compressors, and reverb units work best when you process the entire signal, so they are commonly used with inserts. The reason for compressing a vocal track, for instance, is to limit its dynamic range. Unless all of the vocal's signal is sent through the compressor (through a channel insert, perhaps), a portion of the signal will retain its original dynamic range, thus preventing you from keeping a firm lid on loud passages.

Instead of using the channel insert, you can patch the compressor in-line with an outboard mic preamp while tracking the vocal or route the output of your recorder through it while mixing. But if you need a mixer's pad and input preamp to optimize the signal level before compressing it, the channel insert is the best place to patch the compressor into the mixer.

An outboard equalizer is another signal processor that can be used in a channel insert. If you have a bass-guitar track, for example, that is boomy in the 100 Hz range, patching an equalizer into the track's channel insert will let you reduce the desired frequency. Because 100 percent of the bass guitar's signal flows through the equalizer with that setup, none of the signal will escape the EQ's corrective influence. Other effects that work well in channel inserts include aural exciters, which generate harmonic distortion to make a track sound brighter and louder, and the BBE Sonic Maximizer, which corrects unwanted phase shift and enhances transients.

Using an insert requires an insert cable, which typically has a 3-conductor -inch TRS plug at one end and a pair of 2-conductor -inch TS plugs at the other. On most mixers, the ring of the TRS plug sends the signal to the processor, and the tip returns the signal to the mixer.

Do Not Insert
Although you can patch a time-based effects processor (such as a digital delay, a reverb unit, or a multi-effects processor) into a channel insert, there are several reasons not to do so. To begin with, you have to adjust the processor's onboard wet/dry mix control to set the level of effect you want. Many effects processors have an inversely proportionate wet/dry mix control. That means when you increase the dry output level, you simultaneously decrease the wet output level and vice versa. That type of control works fine with mono chorus and flanging effects, in which you generally want a fixed 50/50 mix of wet and dry signal. However, it's difficult to adjust the mix on delays or reverbs in a channel insert if your processor doesn't offer independent control of the wet and dry output levels.

Say, for example, you want to raise the reverb level on a vocal track during mixdown without lowering the amount of its dry signal in the mix. A processor's inversely proportionate mix control won't enable you to do that, because increasing the wet signal using that control will lower the dry signal at the same time, defeating your purpose. A few effects processors offer a discrete dry output, but patching the dry output to your mixer will use up another line input, which may not be available.

Furthermore, if your mixer offers fader automation, you'll be much happier recalling reverb levels on your mixer's aux-return faders than manually restoring wet/dry mix settings on your processor. Many effects processors do not store the wet/dry mix control's settings in RAM, though devices that control that parameter in software often do. Regardless, adjusting the wet/dry mix at the mixer using an aux send is much easier and faster.

Last Resort
Although the best way to process an individual track with reverb, echo effects, and stereo chorus and flanging is by using an aux send, sooner or later you will run out of available aux sends for that monster mix you're working on. If an extra effects processor is needed for one track only, don't hesitate to patch it in using the channel insert. A mono effect can be returned to the mixer channel's insert-return jack and the processor's wet/dry mix control used to set effects levels. Even though it's not the best way to add time-based effects to a track, sometimes it is the only available way. In that case, go for it. A good last resort is better than no resort.

When using the described routing method to add one last stereo effect to a mix, the two effects-processor outputs can be patched to a stereo aux return or to two available line inputs on your mixer. Because the processed sound is not returning to the board through the channel insert, you can set the processor's wet/dry mix to 100 percent wet and control the effect's return levels at the mixer.

There's one catch, however: unless the track's dry signal returns to its channel insert, you will not hear anything on the original channel, because the mixer's insert send is typically internally normaled to its insert return. If the normal is broken by plugging a cable in to the insert jack and the signal is not returned to the insert jack, the channel's dry signal will not reappear on that channel fader. To solve that problem, simply patch your insert send and return connections to a half-normaling patch bay. With the channel's insert send half-normaled to its insert return, you can route a cable from an insert send at the patch bay to an effects processor without interrupting the patch bay's normal, thus preserving the signal flow back to the mixer's insert return.

Channel inserts can be used to expand the de facto number of effects sends your mixer provides. The major drawback is that each insert serves only one mixer channel. In most cases, the best way to add reverb, echo, and stereo chorus and flange effects is by using an aux send.

Another thing to consider is that all signal processors degrade signal quality to some degree. Preventing a portion of the original signal from going through your outboard effects processor by using an aux send rather than an insert lets you retain some of the original signal purity. If you route the track to the effects processor using a channel insert, the entire signal passes through the processor's electronics, arbitrarily degrading the signal to some (albeit small) degree. Depending on the quality of your processor, the degradation may or may not be audible, but it's something to consider. This is an excerpt from the following article: Chain, Chain, Chain Effects.

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