Denoise First Impressions

For the past two years, we’ve been trying to streamline the process of editing our fortnightly podcast so that the whole thing could be done on iOS. And about a year ago, we actually succeeded at putting together a workflow that would let us do everything aside from the original recording on our iPads, but the results weren’t quite as good as we had hoped.

When we use a desktop computer to edit, we rely on Audacity. While we’d love to use a fancier audio editor like Apple’s Logic, the expense necessary for us to each get a copy of it would be prohibitive given the limited audience we have, so we put up with Audacity. One of the nice things included in Audacity is proper noise reduction, and the results from that are quite amazing. For the past year or so, I’ve had to record from the laundry room where the furnace is, so my audio track frequently has a hum in the background I want to remove. Audacity’s noise reduction facilitates this greatly.

When we edit on iPads, we use Ferrite. Ferrite is an audio editor that was pretty much tailor-made for certain podcasting workflows, and while it doesn’t map entirely to ours, it is the tool that enables us to edit with the least amount of hassle on iOS. One of the things that was missing from Ferrite that really annoyed me was noise reduction. In its place was a noise gate, which mutes an audio track if the background noise is below a certain volume threshold. This is perfectly serviceable during summer, because the amount of background noise is low enough that even if it’s still present while I’m talking, it isn’t really apparent. However in winter, it’s abundantly clear that there’s background noise while I’m talking and that made me frustrated. In the cases when it was really audible, I had to revert to editing on the Mac because there wasn’t really a solution to the problem natively on iOS.

During our initial investigations into editing on iOS, we found WavePad, which is a cross-platform audio editor that also happens to exist on iOS. It had noise reduction not unlike what you could find in Audacity, but the primary issue we had with it was its limited options for loading and saving files. You could only load and save files that were copied to the iPad via FTP or iTunes File Sharing on a computer, and in our opinion, if you need to involve a computer in the process at all, you might as well just do the editing there in the first place. The app never was patched to add more options for file loading and exporting, so we had to give up on using that app.

Earlier this week, I searched the App Store and found an app called Denoise. Denoise was made primarily as a tool to do noise reduction for videos, but there is a “voice memos” section of the app that can handle pretty much any audio file you throw at it. I decided to give it a spin during this week’s editing process.

It was immediately clear that this app was really engineered with shorter length files in mind. If you throw an audio file longer than eight minutes at it, it will only load in the first four minutes of audio as a sample. This has good and bad implications. It’s good because actually running the noise reduction takes incredibly long (more on that in a bit), so only running it on four minutes while you’re dialing the settings just right means you have a quicker feedback loop. The bad part is that you’re meant to select the noise sample that the reduction will be based on in that four minute slice, and if that slice doesn’t have a good 10-15 seconds of noise to grab as a sample, the effectiveness of the noise reduction is greatly reduced.

Of course, the usefulness of a 4 minute sample of the final output is only good if it’s consistent with the results you’ll get after running it on the whole file, and this is where I encountered issues. Strangely, I only encountered these issues on my personal voice track, and not Luc-Olivier’s. The preview clips were all fine, but upon exporting the full file, the levels were way too low and my voice sounded like it had a flanger or phaser effect atop of it for the whole 88 minute length of the file. So that’s not too good.

On top of that, it took 13 minutes and 18 seconds to run the voice reduction on an 88 minute minute file. Audacity’s noise reduction would normally do the same thing in around 2 and a half minutes on a desktop computer. Again, I would be willing to live with the tradeoff in performance if it would reliably produce good results. It’s just that having to wait 13 minutes for each iteration to render just amplifies the problem that the preview is inconsistent with the final results.

I’m not sure what in specific made my voice track have issues. I used Denoise with my voiceover for this weekend’s Swan Song video and it worked fine when the file was of much shorter length, so maybe it’s a length thing? Maybe the length of my noise sample was too short with the Limitless Possibility voice track and that meant it couldn’t do its job efficiently. I really don’t know.

After fiddling with the settings for about 90 minutes, most of which was spent rendering, I did find a combination of settings that worked on my problematic file. It’s just unfortunate that there’s no way to save presets in the app, so I’m going to have to refer to a screenshot of the UI to recreate the same settings in the future.

Despite all of my complaints, I’m happy this app is out there. There have been one or two other apps in the App Store that have claimed to do noise reduction in the past, but they were so old or badly written that they would straight up crash when trying to load our hour-long voice tracks. Now we have something that with a lot of massaging can get decent results, so it made something we flat out couldn’t do on iOS before possible, and I am appreciative of that. That said, a lot of improvements could be made to this app to make it a reliable workhorse, and I hope we see some of those in the coming months to ease the pain.