BOOM LIBRARY SFX ADVENT CALENDAR
DAY 14 – AXEL’S HINT: DENOISING
In today’s SFX Advent Calendar, BOOM Library’s Axel Rohrbach shares a useful hint when it comes to denoising source recordings. Enjoy and keep it in mind 🙂
Denoising using Multiband Expansion
Nowadays denoising is a bit easier, less expensive and of higher quality than it was a couple of years back. I mostly use iZotope RX either as single audio suite plug-in, in stand-alone mode or using the new and very cool “Connect” feature. However, sometimes I need something different. My second most used denoising technique after using actual denoising tools like RX is restoration with multiband expansion.
First of all, here is a very short recording of a piece of metal, used for a soldier in a trailer I was recently working on. I compressed the recording quite a bit for this little tutorial so that the rather broad band noise is getting even louder. Here is the example:
In this case I am using Fabfilter’s “Pro-MB” multiband compressor, which can also do expansion and upward compression but basically every multiband expander can do the trick. First thing I did was picking several frequency bands and lowering the range per band (or gain of the band when using the expander function) so that I got the noise within the specific band as low as wanted. Then I set the threshold right above the noise floor, so that the expander wouldn’t react until the material was louder than the set noise threshold.
Using Attack, Release, Ratio and Knee, the most tricky part is to get the expander working without changing the sound minus the noise in its original version.
In Fabfilters “Pro-MB” you can see the actual process of the dynamics as an orange line covering the whole spectrum. What you want to create here is a flat line at the time when there’s material coming through that you want to use. I wanted the noise to still be lower so I put another instance of the “Pro-MB” in the chain, lowering the noise floor even more.
I took the screenshot precisely at that moment when my sound was at the peak and as you can see, the orange process indicator comes as a perfect flat line. This visual feedback helps me to see that, at least at this exact moment, the peak is very similar to the original in terms of the frequency response. Surely, some kind of processing is going on. The result of putting in another instance can be heard here:
So, why would I use this instead of doing such a thing in iZotope? There are three reasons: firstly, I can do it within a session without any need to destructively render the audio with all its benefits, most of all the possibility to automate. Secondly, I can still alter the settings whenever I want or when needed. Thirdly, for me that is the easiest way to only remove specific frequency bands instead of broadband de-noising as in this example. Let‘s say I only have a high hiss in a record. I could set up an expander only working in this specific band. Or if there are low, rumbling, distant traffic noises: I can set up a low band expander only to get rid of that noise floor without losing the low frequencies on specific impacts or hits.
I hope this offers you a helpful alternative for any challenging situation you may run into and you’ll be able to make good use of it.
Cheers,
Axel
