Brusfri, which is Swedish for ‘Noise Free’, is a simple‑to‑use noise‑reduction plug‑in that supports all the usual Mac/Windows plug‑in formats, including AAX (and has been optimised for Apple’s M1 processors), as well as AUv3 for iOS. It’s designed to attenuate steady‑state noise using the established technique of analysing a short section of ‘noise‑only’ recording. This information is then used to set the thresholds on a large number of expanders/gates, each working on a narrow part of the frequency spectrum. It’s an approach which can be very effective on hum, noise from fans, electronic hiss and so on, but can’t fix clicks and pops or any noise which changes radically in character over time.
You only need a second or two of noise‑only recording for the process to work. Learning this sets the thresholds for the expanders, but the user can also make manual adjustments to the overall threshold level and to the attack and release times of the expanders if required by dragging on the graph at the left of the GUI. An eye icon enables or disables lookahead, which adds a few milliseconds to the overall latency when active, but does give the processor advanced warning of transients. A Treble control is included as heavy denoising can sometimes rob the original signal of a little high end.
The Learn process entails holding the Learn button for the duration of the noise sampling period, after which the expanders are set up automatically, but there are a few additional controls that may be useful for fine‑tuning on some sounds, since, especially where there’s a lot of noise to deal with, the processing can have an impact on the higher‑frequency harmonics of a sound, particularly at the ends of decaying notes. The Treble control can be used to add some compensatory HF boost, while Smooth essentially changes the ratio of the internal expanders, producing smoother results at the expense of being less assertive against heavy noise. HPF sets a low‑cut filter in the detector sidechain to prevent very low‑pitched noises (such as microphone wind noise or stand vibration) from dictating the terms. Mix adjusts the balance between the processed and unprocessed signal and in most cases adjusting this until the noise falls to an acceptable level produces more transparent‑sounding results than always trying for complete noise removal.
I found Brusfri (v1.21 at the time of writing) easy to use and very effective against constant background noise such as hiss, aircon fan noise and steady ground‑loop hum. The more noise you try to remove, the greater the risk of affecting the high end of decaying sounds such as acoustic guitar or piano, but if you only need to drop the noise by up to 12dB or so, Brusfri will usually deliver good results.
Conclusion
Brusfri might not be the latest in noise‑reduction technology — there are advances being made with AI in this field now — but it’s not super expensive, it works on a proven principle, and has the benefit of being easy to use, whether you’re reducing the background hum and noise on a guitar track or cleaning up a vocal part recorded in less than ideal conditions. It also avoids producing the kind of chirpy processing artefacts that some noise reducers do too often, and that’s a very welcome bonus. It’s a good, solid addition to the Klevgrand range, then, and it may be the only noise reducer that many users will ever need.