Arboretum Restoration‑NR.
PC DirectX only
Restoration‑NR (latest version 1.1.1) is another denoising DirectX plug‑in from Arboretum. A rather more advanced version of Ray Gun, it still uses an expander, but this has a multi‑band algorithm that can adapt to different noise prints far more accurately. There are two settings: the normal settings use 512 filter bands, while clicking on the HiRes button increases this to 4096 bands, giving better noise reduction at the expense of greater processor overhead. However, even on the HiRes setting, Restoration‑NR only tied up about 10 percent of my Pentium II 300MHz.
There are two ways of finding the best noise print. The quickest is to click on the Guess button while playing the file in question — the plug‑in makes an educated guess at the nature of the noise component. However, if there is a small section of the file containing just background noise, this can be separately analysed using the Learn button, and this provides a much more accurate result. You can also Load and Save noise prints for later use.
Like Ray Gun there are again two main controls, Threshold and Attenuation, which are set up in much the same way. To combat the high‑frequency loss that often accompanies noise reduction, there is also a high‑frequency Boost facility that provides you with up to 12dB of boost above a user‑definable Hi‑Cutoff frequency. Since this is after the noise reduction, it doesn't reintroduce any constant background noise.
In use, Restoration‑NR is (as you might expect) significantly better than Ray Gun at reducing background noise while leaving the desired signal relatively unaffected. Thankfully the controls are all calibrated in this latest version (previous versions had no markings at all, not even for filter cutoff frequency), but the user interface could still be improved — a plot of the noise‑print frequency response, as provided by many other plug‑ins of this type, and a means to audition just the portion of the signal being removed would make setting up much simpler.
After some practice I certainly achieved effective reduction of background noise levels, but it still proved remarkably easy to overdo things and remove desired programme material along with the noise. I also noticed some slight level pumping. At this price other products, such as Steinberg's DeNoiser, have fewer interactive controls and seem generally easier to use, while still providing effective noise reduction with most modern material. However, as its name suggests, Restoration‑NR can be effective with older material as well — it was a clear winner with a 1927 recording drowning in surface noise, when every other NR plug‑in I tried was left floundering. If you indulge in 'audio forensics', this could prove just the job... and at extreme settings it could just double as an underwater sound effect! Martin Walker