Soundtheory Gullfoss Review: Smart Real-Time Automatic EQ

Gullfoss is an intelligent real-time automatic equalizer plugin, reacting to audio material to reduce harsh frequencies and solve issues with frequency balance of the signal.

The EQ’s parameters can change more than 100 times per second. It uses a unique computational auditory perception technology developed by Andreas Tell, who has a background in theoretical physics and the foundations of quantum physics in particular.

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He’s been studying human auditory perception since 2005. He says that their “signal processing methods took a few inspirations from quantum theory too.” Gullfoss can achieve things not achievable by regular EQs, and fix issues immediately that would otherwise take a lot of time to fix. The auditory perception model makes objective processing decisions, and using the ‘Golden Ear’ that’s been built into Gullfoss can allow your mixes translate better across all systems.

The interface is clean, fast and simple. You can drag the red barrier lines along the frequency spectrum to constrain the processing between their confines, and you can even move them past each other to only process the lows and the highs, preserving the middle.

The Gullfoss UI in action

The Equaliser Graph Display is crisp and clean, showing real-time EQ changes visually. This can show you the processing Gullfoss is performing. It can even inform changes in the mix – if Gullfoss is consistently boosting a certain frequency range by a lot, users might go back to the mix to fix balance issues they would have missed without Gullfoss. Alt-Clicking values will alternate between zero and the last value (imperative for A/B testing to make sure your processing is making a positive impact on the signal).

The Tame and Recover parameters reveal masked signal components to improve clarity, detail and spatiality, by suppressing overly dominant/harsh signals (Tame), and increasing signals that are dominated by others (Recover). Bias allows users to choose Gullfoss’ preference in borderline cases, positive values lean towards Recover, negative values rely on Taming more often. Brightness is a general tone control, higher values increasing higher frequencies and lower values suppressing them, with a value of zero supplying a balanced frequency spectrum. Boost simulates the change of frequency balance as perceived by human listeners when the volume is changed, emphasizing bass frequencies and reducing mid frequencies.

When to Use It?

Gullfoss can be a helpful tool on all sorts of material – single tracks, vocal tracks, the master bus and more. On vocal tracks, it can be used in a way similar to Soothe to reduce harshness and de-ess in a certain frequency range. It’s an incredible tool for balancing and mastering, especially for producers without the most accurate monitoring situation.

I’ve even used it in situations where TV shows and movies sounded overly harsh in a particular listening environment – Gullfoss can clean any signal. That being said, it’s easy to overdo (many situations using it on the master buss might not need more than 4% on the Tame parameter).


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  • Unprecedented real-time automatic equalization, unique modern functionality no other plugin on the market can perform
  • Widespread applications, usability
  • Objective processing decisions
  • Improves spatiality, separation of elements, detail, definition
  • Reduces harsh resonances and mud
  • Preserves dynamics quite well
  • Mixes more consistent and translatable across listening environments
  • On extreme settings, can be a creative sound design tool as well


  • Only available for OS X (Windows version coming this year)
  • Intense CPU usages with multiple instances running with the GUI open
  • Overdoing it can quickly do more harm than good, exercise caution and use your ear to find the proper balance between reducing resonances and retaining some grit
  • Using Gullfoss on lower quality mp3s can serve to bring out artifacts from the mp3 encoding – that being said mp3 encoding artifacts are primarily in the upper frequencies so using the upper preclusion bar to reduce or stop the effects on those higher frequencies



Gullfoss is an impressive innovative offering; in a time when folks are asking if plugins are actually getting better versus just being repackaged, Gullfoss’s real-time equalization is the former.

Price and availability

Gullfoss is now available for a special introductory price of $99 USD at (regular price: $199.00)


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