Envision the signal chain of a guitar and pedalboard. The first image that comes to mind is probably a cable coming out of the guitar flowing into the input of the effects pedals—the moving along from one pedal to the next—and the output of the pedals going into an amp, mixing, or recording device.

This is known as a serial signal chain, and it’s the most common type of setup for guitar players. But what if guitar players want more creative control over their sound? A way to expand tonal possibilities in ways that simply isn’t possible with serial processing?

That’s where parallel processing comes in. Let’s go over what it is, the benefits it brings, some concerns that arise from running this type of processing, and how to design it in a guitar rig.

What is Serial Processing?

Most guitar players use a serial processing setup in their signal chain. This is the example listed above, where the signal flow goes guitar > one effect pedal to another > output device (amp, amp simulator, or DI into a console or recording interface). This is a tried-and-true method for a lot of reasons. It’s easy to design and connect, is convenient for moving around between live shows and recording sessions, and provides a linear way to stack the chain of effects.

Pedal order is a critical factor, as every pedal will affect the sound of those after it. The general order in a serial signal chain is gain pedals like overdrives and distortions, then filtering and modulation, then time-based effects such as delays and reverbs. There are no set rules on how to order them. But experimenting with pedal order in a serial processing effects chain has its limitations though, due to its linear nature.

What is Parallel Processing?

Parallel processing is more complicated—but the complicated nature is what holds the appeal. Conversely to the linear flow of serial processing, parallel processing is lateral, and allows the operation of multiple signal flows that can be mixed and blended.

Let’s dive deeper into what parallel processing is, the benefits it provides, and some challenges to be aware of.

Parallel Processing in Recording

To understand parallel processing better, let’s briefly examine how it’s used in recording. It’s a common technique used in modern recording production, and drums are the perfect example. You have the drum buss group that contains the individual microphones: overheads, snare, kick drum, toms, et al. These are mixed using standard processing like EQ, compression, and saturation.

A separate stereo buss is created and the audio output from the main drum buss is sent to its input. This buss is processed much more heavily than the original with more extreme levels of compression, saturation, or whatever tools are needed to get the sound the engineer is looking for.

On its own it rightfully sounds way too processed, but that’s the point. This buss is then blended in with and underneath the original. The heavier processing adds weight and power to the overall drums that gives it a “larger than life” sound that’s not possible with the standard processing on the original drum buss alone.

This is one practical example of parallel processing. Both busses, the original and parallel, work together and are summed for the final instrument sound. It’s a technique that can be used on anything, not just drums. Vocals, instrument groups, bass and guitar, even the entire mix.

Benefits of Parallel Processing

Parallel processing in a guitar rig offers multiple benefits. These vary depending on how the signal is routed, and one of the main benefits is the ability to distinctly mix clean and effected signals. This preserves the original guitar tone and reduces the impact that running the signal through multiple pedals has on it.

It offers the ability to have multiple (usually two) independent processing paths, which opens up a number of creative options when it comes to rig design and signal flow.

Challenges of Parallel Processing

There are some drawbacks to parallel processing techniques in a guitar rig. The biggest thing to be mindful of is phase issues. Splitting the guitar signal inherently introduces phase alignment concerns. You’ll know if you’re experiencing an out of phase signal because the guitar sound will be uncharacteristically thin-sounding.

Phase alignment issues can happen along any point when you have multiple signal chains, and you’ll want to start with something that properly splits the signal without introducing any phase issues at the dividing point. Some pedals are designed to accommodate parallel processing to make more complex routing easier to manage.

Each channel has a volume knob so you can set the output levels, but since a device like this sits at the beginning of the chain (using it as a splitter) then you’ll have to properly gain stage any pedal that comes after it with their respective controls.

Building a Parallel Processing Signal Chain

When it comes to building a signal chain for parallel guitar processing there really are no rules. And that’s the whole point! Creativity is the name of the game here. The first place to start is with how you’ll split the signal.

This can be done with a router or splitter like the Radial Engineering BigShot AB/Y or Old Blood Noise Endeavors AB/Y. Both are A/B/Y switchers that let you output two separate signals or split a single signal into two.

Ideas for Parallel Guitar Processing

When it comes to effects to place in a parallel processing chain, this is where it gets fun. There are endless ways you can design a parallel chain, so let’s go over a few of them.

You can use one for gain and filtering and another for modulation, delays, and reverbs and blend them together. Most guitar tones live and die by the type of gain pedals they’re built on, so you could consider running two main overdrives, distortions, or fuzz boxes and stack them to get the best tonal benefits of each.

But it’s with more unique effects like modulations and time-based effects where things start to get really interesting. Running delays in parallel provides a much cleaner mix effect than running them in series, as they’re not stepping on each other so much. U2’s The Edge is legendary for this type of sound.

Factor in more esoteric effects pedals and things move to a whole new level. Loopers like Electro-Harmonix 95000, pitch shifters like the DigiTech Whammy DT, and octave pedals like the BOSS OC-5 are inherently unique and versatile. But when you integrate them into a parallel processing setup there’s no limit to the sounds you can create.

Lastly, consider the fact you’ll need somewhere to send the parallel signals. A lot of guitar players use a dual amp setup for parallel processing. Beyond the effects in each signal, you can open up even more tone options by using different amps.

Guitar god Eddie Van Halen was notorious for using a wet/dry/wet setup toward the end of his career. In this type of rig design he had three cabinet setups on stage. In the middle was the dry signal, and on either side of the stage different effects were routed based on what they do. This created a larger than life guitar sound, as if he didn’t have that in his fingers already!

If going direct you’ll need at least two free inputs on whatever device the signal is flowing into. And if the end device doesn’t have a DI setting you’ll need to get a stereo DI like the BAE PDIS or a DI for each processing chain like the Warm Audio WA-DI.

Conclusion

By integrating parallel processing into your guitar rig you can open up worlds of sounds that aren’t possible otherwise. There are plenty of signal routing tools to help you route things the way you want, and some go beyond that by adding features like crossfading and envelope control for manipulating multiple signals even further.

In the end it all comes down to experimentation. With a little out-of-the-box thinking you can design a parallel processing signal chain for your rig that sparks creativity and go far beyond what’s possible with a standard serial signal flow.

Brandon Stoner is a lifelong musician and audio engineer who owns more guitars than anyone needs. As a lover of all things writing and music technology, he crafts every piece with his dog Max on his lap.

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