Sound Theory Gullfoss DAW Plugin

Updated: Feb 12


It's no secret that the world of DAWs is evolving quickly with more sophisticated software packages and plugins coming out all the time. It's also quite clear that many aim to replace existing physical gear or make the whole recording and production workflow faster.

In a world where competition for streaming real estate is fierce, a quick and effective workflow is essential. Let's be honest: major bands in the 70s or 80s could afford months in studio perfecting their albums as when they came out they were the talk of the town for months or even years. In this day and age of fast food-like consumption of media, putting out less content more often seems to be the name of the game. Thus getting to results faster allows for more content output with the same effort.

Enter ideas like Gullfoss from Soundtheory. This DAW plugin aims to resolve EQ issues in a mix dynamically, using proprietary algorithms (or in their words "unique computational auditory perception technology") to enhance a mix on the fly, solving frequency issues as the music progresses. This could speed up the whole production process quite significantly if used wisely.

We came across this technology at Winter NAMM 2019 and decided to give it a spin.


The plugin was fairly easy to install and requires minimal configuration. Once installed you will be able to see it when you select effects for a particular DAW channel strip or for the DAW's main mix. On a Logic Pro X channel strip you can insert it in the effects chain like a regular EQ plugin. From there you can pop it out, register you license and adjust its controls.

Sound Theory Gullfoss
Sound Theory Gullfoss

The controls are explained in a one-pager PDF which you can download for their website:

Soundtheory Gullfoss Overview

This is a summary of what the controls aim to achieve:

Tame and Recover: pretty straightforward controls, as one will quiet down signal components that may be dominating others, and recover will bring up other components which may be masked by the dominant ones or not clear enough in the mix.

Bias: sometimes signal components can be borderline. If the algorithm is unsure whether the component should be tamed or recovered, it will use this control to bias its decision. Positive values bias towards recovering, while negative values will give preference to taming.

Brighten: there is a more detailed explanation in the documentation provided above, but essentially this allows tweaks to brightness as the algorithm is genre agnostic and preferences may vary.

Boost: same as brightness, but for lower frequencies. These two controls will allow you to adjust the final result to your preferences.


For the testing we've chosen to evaluate how the plugin would act on guitar modelling sounds, and for that a Line 6 Helix Native was used. Guitar amplifier modelling has been around for quite a while, and it has advanced significantly. Like any technology it has its quirks - put many digital effects in sequence and some unnatural artefacts can emerge. Also the frequency response of its output can be a bit irregular depending on how the modelling amplifier is set and what cabinet simulation or IR (Impulse Response) is being used. Finally we do know that many guitars in a mix can have quite a battle for frequency and amplitude real estate.

The Helix Native we utilised had a preset consisting of all the elements of a typical guitar signal chain: compression, overdrive, power amplifier and cabinet. We've chosen to turn off any modulation or reverb effects to give the plugin the chance to treat a raw overdriven or distorted guitar signal.

Helix Native Signal Chain
Helix Native Signal Chain

The first experiment was to go from the Helix Native straight into the Gullfoss plugin on a few selected guitar tracks, for example one for rhythm and another for solo guitar. This allowed us to run two instances of the plugin on two different tracks and see what is the result of them individually and combined - in a mix - but with the plugin receiving context from its own track only, not the whole song.

Gullfoss on Rhythm Guitar
Gullfoss on Rhythm Guitar

Gullfoss on Solo Guitar
Gullfoss on Solo Guitar

The results were quite interesting. By adjusting both tame and recover controls we could see and hear some improvements in the overall EQ. This was then dynamically following the music, without any noticeable artefacts, which was quite impressive. Important to notice that in both cases the guitar was the only signal delivered to this plugin, so whatever clash of frequencies it was trying to resolve were results of unbalanced frequency response coming out of the amp modeller (or my sloppy playing), and not a result of instruments fighting for frequency response real estate in a mix. The pictures are static but the results are quite dynamic and change as the song progresses.

We also did try routing all guitars to an aux bus and applying the plugin to that instead of the individual tracks, and the results were quite similar, perhaps slightly better as the plugin now has knowledge of both rhythm and solo guitars at the same time.

Plugin Enabled on Aux Bus Guitars Only

The other alternative we've tried was plugging the Gullfoss at the end of the mix of the same song with the same guitar tracks, but then turning the instances plugged into individual guitar tracks off. That way it would receive context from both guitars at the same time as well as drums and bass.

Logic Pro X tracks used for testing
Logic Pro X tracks used for testing

The results here were even more impressive; with full context of the song this plugin really shines. The overall brightness and clarity was significantly improved and all it took was tweaking two knobs - as we did leave the brighten and boost controls alone for most of the testing, and didn't use the bias much. Doing this by hand would require mad automation skills and auditory perception. Hear the comparison and you should be able to see the difference in the clarity of the guitar sound and the overall balance of the mix, even considering that this was just a rough 'pick up your guitar and play' kind of experiment.

Gullfoss on Stereo Out
Gullfoss on Stereo Out

Overall Performance

For the tests we've utilised a 2017 iMac with 3.6 GHz Intel Core i7, 16GB of RAM and mac OS Mojave, running Logic Pro X 10.4.4.

The CPU load was fairly low (around 5% in addition to Logic Pro X itself and the multiple instances of Helix Native), with almost negligible additional RAM consumption even when running multiple instances of the plugin.

The bounced tracks didn't present any additional artefacts in comparison with the original dry versions without the plugin.

During the testing no crashes or noticeable bugs were observed; the plugin was very responsive and quite easy to use.


There is no doubt that this plugin could save hours of work and make workflows for final mixing and even mastering far simpler. It allows inexperienced mastering engineers or mixing engineers to fix issues they didn't even know they had. It saves time for professionals by automating something that would take much longer to do manually.

On the tests we ran we noticed that context matters quite a lot, so on a busier mix you really see the value of having this plugin in your chain. Since these tests were heavily geared towards guitar sounds, we would recommend checking out other reviews and also the examples they have on their website, which do include outputs from other types of instruments and mixes:

Sound Theory home

If you want to purchase the gear we're used for these tests, here are some Amazon links for RME Babyface pro, Universal Audio Apollo, Rupert Neve DI and Ibanez RG8570z:


Universal Audio Apollo Twin MKII Duo APLTWDII

Rupert Neve Designs Active DI Box

Ibanez RG8570Z J Custom - Black Rutile

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