Fixing Field Recordings with Absentia DX: A First Look


I experienced a series of surprises while browsing my Twitter feed earlier last month. The first was an announcement of Todd-AO’s new dialogue noise reduction software, Absentia DX. The second was that it was produced by respected Hollywood sound supervisor and field recordist Rob Nokes. The third was that it was priced at $49.

Now, I have zero experience editing dialogue for feature films. So, why would this announcement intrigue me? Of course, I didn’t expect to be cutting dialogue. Instead, my first thought was: “can this work on field recordings?”

I emailed Nokes. I asked if it was possible to use Absentia with sound effects. He mentioned that his teams were already using it with Foley tracks. That was all I needed to know. I purchased and installed the software a half hour later.

How well does Absentia work with sound fx tracks? Will it improve troubled field recordings laced with buzz or noise? Does it have potential to rival iZotope RX’s noise reduction software at a tenth of the price? Can “Absentia DX” serve as “Absentia FX?”

In today’s post we will find out. In this “first look” article, we’ll see if a dialogue noise reduction tool can be hacked to help master damaged sound effects captured in the field.

Introduction to Absentia DX

Absentia DX, or ABDX, is noise reduction software designed to fix three types of audio problems in dialog recordings:

  • Hum.
  • Broadband noise.
  • Ticks.

It works as a no-nonsense batch processor: select folders or simply drag and drop files, folders, or entire volumes onto the app. It will then chug away and repair the audio, either replacing the old files or creating new ones as you prefer. It does all this while preserving existing metadata, too.

The drag-and-drop workflow is a compelling way to apply processing to a massive amount of sound files. Now, it’s important to note that the app doesn’t aim to be a one-stop replacement for every audio problem infecting your tracks. Instead, ABDX is meant to diminish mundane, lowest-common-denominator labour. The idea is that by removing the most common problems, the app allows an editor to focus their expertise on repairing the trickiest audio problems instead of wasting time on low-skill issues.

Those are the broad strokes. I reached out to Rob Nokes to learn a bit of background and purpose of the new software. He kindly shared why and how ABDX began.

Absentia Emerges

Creative Field Recording: What inspired you to create ABDX? Was it a due to particular experience, or project you were working on? Was there one moment when you thought: I just have to create this software?

Rob Nokes: For along time I have been a hardcore RX Advanced user and was in RX endorsements that ran on YouTube. Let me first say, RX is the undisputed king, the people and product changed professional audio for the better. What inspired me was the endless repetitive manual tasks that I was performing with RX, hours of monotonous repetition each week. The RX people asked me for a wish list and I replied but never got a response. I requested again and nada. So I hired three developers and simultaneously developed Absentia DX (originally it was called "Hum Remover") with three different development teams and then chose the most promising path. Immediately I knew this would save me alone one hundred hours per year of removing hums and harmonics, not to mention save the re-recording mixers I work with the same amount of time.

CFR: Can you share a bit about the experience of developing noise reduction software? Did it take a long time? Did it involve beta testing in studios, etc?

RN: Absentia DX was developed over 8 months and as soon as it was stable we started using it on our TV shows. The Tick and Prison Break were the first shows it was used on. We would A/B the original with the ABDX audio and refined the results with seventy beta versions. We collected a wide dynamic range of production sound rolls that provided us ample material for thorough testing on each version. All the beta testing was done on our own shows, when we made a mistake we had to pay the price of going back to the original sound rolls, when you pay the penalty for poor performance it quickly trains you to improve your results. Only in December did we first release it to close friends around the world for testing.

CFR: It must be rewarding to see something you have worked on be embraced by the community. Have you been pleased with the community response and the release?

RN: It is absolutely is. When peers recognize the ingenuity and labor-saving benefits of ABDX it makes us feel good that all the effort was worth it. When re-recording mixers and supervisors tell me how transparent hum remover it is awesome. For me personally I would use ABDX because it has saved our editorial team 72 hours of hum removing on one show alone. It would be great if more people understood our goals; 1) remove the obvious 2) reduce manual labor 3) retain the integrity of dialog. Anything beyond that should be manually cleaned with traditional methods. It has also worked quite well for quick sound effects cleanup.

CFR: Do you have plans for integrating the software in other ways, such as plug-ins, and so on?

RN: Many users are asking for a plugin so we will head in that direction. We also have more labor reducing features in development.

Thank you to Rob Nokes for sharing this info about ABDX.

Getting Started with Absentia DX

Note: this “first look” considers version 1.18 of the software.

Absentia DX (MacOS 10.8+, Windows 10, 8, 7, Vista, Server) can be purchased from Todd-AO’s website or Amazon for $49. Purchasing on Todd-AO is via a straightforward PayPal checkout. Downloads (61.8 MB) are available immediately after purchasing. A serial number is delivered within minutes via email.

Installation is a simple affair of opening the DMG file and dragging and dropping the file into the MacOS’s applications folder.

The Absentia DX Interface

Let’s take a look at the app window. The ABDX interface is divided into three simple sections.

The upper third of the window specifies how the app works with sound files.

Simply drag and drop files, folders, or entire volumes onto this area to begin repairing the audio. Optionally, this area can also be set to scan one folder for files, then dump repaired versions in another. If you like, the repaired files may be prefixed or suffixed with any text you choose. Or, the new files can simply overwrite the old ones.

The middle area specifies how the audio will be processed:

  • Hum Remover. When checked, this option allows strong, smooth, or broadband processing. What’s the distinction?
    • “Strong” is naturally more powerful. It’s aimed at the loudest, most troublesome buzzes.
    • “Smooth” works best on more subtle audio.
    • “Broadband” is designed to remove IMAX camera noise.
  • Broadband Reducer. This option reduces a “modest” amount of noise. Note that the app is not designed to de-noise dialogue itself. Instead, it reduces noise in the gaps between speech.
  • Tick Remover. Removes subtle clicks. Again, the app processes audio outside of dialogue.

The last option here specifies whether the output is split into mono files.

The final section offers two checkboxes. The first option offers to produce a on-screen report after processing. It can also be exported to a CSV file.

The second option, “Prevent double processing” is especially novel and welcome. Checking this option writes metadata to processed files to ensure they are skipped if they are attempted to be processed again.

Processing Audio Files

Dragging damaged files on the app displays a drop-down progress bar. The app will begin to process up to ten files at a time, progressing through each noise-reduction task in series. It will dump the processed files into the destination folder specified in the upper third of the app. If this isn’t specified, ABDX will simply create a subfolder next to the original file. If files are dropped from different folders, all subfolders will be created alongside the first, original file.

As the processing works away, the ABDX app will show a numbered badge indicating the files remaining to be processed. The app applies a .tmp extension to the working file as it processes.

Processing Specifications

ABDX can process files up to 192 kHz/32-bit WAV files. Impressively, processed files preserve BWAV, Soundminer, Basehead, and iXML metadata.

Processing Time

How long does it take? Well, this depends on your computer’s processor. For my tests I used a 2012 non-retina 13” MacBook Pro. It was powered by a 2.9 i7 quad-core processor with 16 gigabytes of RAM.

The tests in this table consider a 1:00 stereo 96 kHz/24-bit file. It has some nasty buzz and also substantial noise floor.

Repair Setting Original Time Original Seconds Repair Time Repair seconds Processing Factor
Hum removal (strong) 1:00 60 2:39 159 2.65x
Hum removal (smooth) 1:00 60 2:42 162 2.7x
Hum removal (broadband) 1:00 60 2.56 176 2.93x
Broadband reducer 1:00 60 2.54 174 2.9x
Tick remover 1:00 60 1:20 80 1.33x
Hum removal (broadband), broadband reducer, and tick remover 1:00 60 7:16 436 7.26x

I’d imagine the duration is determined by how troublesome the noise is. However, you can use those numbers as a guideline.

Field Recording Tests

I have a hard time parting with any field recording I’ve captured. That’s why I’ve saved up a bank of damaged sound effects. They have noise and buzz problems. I’ve always hoped to have a bit more time to work on them. Thankfully my procrastination provided a lot material to test ABDX on field recordings.

Before I begin sharing the tests, recall that I am using ABDX for purposes for which it was not intended: sound fx processing. The buzz remover, broadband reducer, and tick remover are designed specifically to fix dialogue. With that in mind, let’s see how this “ABDX hack” works on sound fx.

Specific Sound Effects

I used a basic field recording as my first test. It is a studio recording of an office chair rolling on castors. It has a slight noise floor and a subtle hum throughout.

Note: you may download each of these sound files from the media player to test in your own workstation. Some of the issues are subtle and may not translate perfectly via the HearThis audio player. You’re welcome to use the sounds however you like as long as they are not shared, even free of charge.

Here is the original file:

Here is the track processed with hum removal (strong and smooth):

And here it is processed with noise reduction:

And here is the same track processed with both hum and noise removal:

If you listen closely in the gaps between the rolling, you’ll hear that the hum is removed completely. The noise is also diminished slightly. You can see more in the spectrograph:

What’s notable in this example is that the problems have been removed transparently.

For my next test, I tried removing substantial, thick noise from a doorbell.

I ran the broadband reduction on that file. Here is the result:

While ABDX didn’t remove the noise completely, we can observe three interesting things. First, the noise was indeed reduced. Also, no pumping or artifacts can be heard around prominent audio. And, finally, the principle audio was not damaged at all.

The next sound is a field recording of a distant helicopter passing. There is gritty line buzz throughout the track. To be honest, I didn’t have much hope for any app to fix this, but gave it a shot anyway. Here’s the original sound:

And here is the sound processed with ABDX’s strong buzz setting applied:

While the buzz remains, it’s interesting to see the difference in the spectrogram. ABDX was able to identify and remove the issues in the upper register and strip them away.

This next track is a mobile phone buzzing. It suffers from a lot of noise and the faint RF chattering all field recordists dread:

I was curious to see how ABDX handled RF issues. Let’s listen to the result after applying noise reduction and hum removal:

Impressively, ABDX completely removed the RF chatter. While the noise is still present, it is reduced slightly and also transparently. It admittedly was quite thick.

Field Recording Atmospheres

Would ABDX work on ambiences, too? Could it strip noise and buzz from complex environmental tracks?

My first attempt was a particularly obnoxious recording of a hair salon. It has deep, thick noise, and considerable hum:

I threw it into ABDX and crossed my fingers:

I think that track was too much for it. For the first time we can hear aliasing from the extreme noise reduction. While the narrow harmonic bands were removed, the lower, grinding buzz wasn’t touched at all. Given that the app is designed to fix straightforward dialogue, not complex atmospheres, I can’t fault the app for its results here.

I tried a less-complex field recording for my final test. A long time ago I accidentally simultaneously used both a battery-powered mic amplifier and also a recorder's preamp while recording in Prague. The result was about 10 bands of whine through the field recording. Listen to it here:

I set ABDX’s hum removal to strong:

ABDX took it every band of whine in one shot, completely transparently, saving a track I had given up on, long ago.


So, what did we discover by using ABDX to repair field recordings? (Remember that ABDX is meant for straightforward dialogue cleaning tasks, not heavy sound fx processing per se.)

  • ABDX removes low-level ringing, buzzing, or whining problems effortlessly. It identifies harmonics and removes them cleanly and transparently.
  • Complex, gnarly buzz is challenging for the software to tackle.
  • It removes a slight amount of hiss or noise from non-complex sounds. It works best on noise that is shallow and thin.
  • Processing attempted on complex files with thick noise can contribute aliasing or artifacts which sounds like a rapid cycling sound.

Overall, I find that the Hum Remover tool is worth the price of admission in itself. For processing field recordings, I could see it being useful for a simple “fire-and-forget” first pass of cleaning simpler, less complex sound effects: drop the tracks on the app at the end of the work day and in the morning focus on more diligent noise removal work after the easiest problems have been already removed.

I shared these findings with Nokes. He told me that was in line with what he expected. After all, the settings are made so quality is preserved for one specific type of sound: isolated human speech. That said, he shared with me a tantalizing fact: an advanced version is in the works to help with other types of sounds.

The upshot? For $49, Absentia DX costs less than most plug-ins on the market and is a worthwhile purchase for to take a first stab at removing hum, buzz, ringing, and slight hiss from sound effects recorded in the field.

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