six colors

by Jason Snell & Dan Moren

This week's sponsor

Protect your privacy and decipher iOS 11 network features with a new book by Glenn Fleishman. Get 25% off with code SIXCOLORS.

By Jason Snell

Removing podcast room noise, hum, and echo

I produce podcasts featuring different people using different microphones in all sorts of different homes, which is to say that the nature of the sound files I receive from my panelists can vary widely.

My goal is to make everyone sound as good as possible for the benefit of the listener—and eliminate telltale background noises that would come and go as different people speak. As a result, I spend a lot of time (and have spent more money than I’d expected) trying to remove noise from people’s audio files.

This sort of stuff isn’t for everybody—you don’t need to buy expensive software and spend a half an hour or longer processing all of your audio files in order to make a good podcast. (Also, in most cases the best long-term solution is to get your panelists to improve their equipment or technique, not to fix it in post.) In fact, there are times when I wonder if all the work I put into the removal of noise from audio files is something listeners even notice. But I notice. And I do think getting the noises out improves my podcasts.

Anyway, there’s a lot of software out there that will let you remove noise from your podcasts. Most of them work the same way: you “train” the software on a portion of the audio that contains only the noise you want to remove, which is generally a moment when your subject isn’t talking. In that moment of personal silence, the recording is pure noise: the whirr of a laptop fan, the buzz of a heater, and the hiss of a microphone that does a very good job of picking up room noise.

If you’d like to try this out, consider Audacity, which is free and offers a de-noising plug-in. Another option is the $149 SoundSoap. Adobe includes a de-noising effect with its audio-editing app Audition. As for me, for the last year or so I’ve been using the $249 iZotope RX 5, which is a combination of audio utilities that let you de-noise, de-hum, and de-reverb audio.

Here are some before-and-after samples. We’ll start with a particularly noisy track from my pal David J. Loehr, which may have actually been recorded in a hotel room, not his usual location. From the waveform, you can already tell this is a noisy track: The big spikes are when David is talking, but when he’s not talking there’s still a pretty thick line. That’s the sign of background noise. (There’s also a big empty gap in the middle; that’s when David muted his microphone entirely.)

iZotope RX 5 also provides a second way of visualizing audio, which is via an orange-tinted interface that indicates noises at specific frequencies. That’s most visible across the bottom of the screen. Those solid bars are background hums—they sit at specific frequencies and just keep on making noise.

Most de-noising plug-ins will take care of background hums, but iZotope RX 5 offers a separate de-hum plug-in that is especially effective at destroying those hums. To remove the hum, I select a portion of the audio that contains the hum and click the Learn button in the De-hum window. Then I select the entire track (or at least the portion of the track that contains the hum) and click Process to remove the hum from the selected area. As you can see in the image below, after I click Process the two orange bars at the bottom of the waveform have vanished from the selected portion of the audio file. That hum has vanished entirely.

While removing the background hum is a major part of the noise-removal puzzle, there’s still other background noise. That’s why I’ll now select a portion of audio and click Learn on the De-noise window. Then I select the entire track (or the portion of it containing the noise I want to remove) and click Process to remove the noise.

As you can see from the image below, the area I processed shows up with the thinnest of waveform lines and appears largely black, with no overlaid orange speckles indicating noise. This “silent” part of the track is now truly silent.

In truth, most of the “silent” portions of my guest’s audio tracks aren’t ever heard by podcast listeners. Whether you use a noise gate or a Strip Silence feature like Logic Pro or Ferrite (that’s my approach), quiet portions of someone’s audio tracks are automatically squelched.

The value in removing noise isn’t making the quiet parts quiet—it’s making it so that the parts in which your panelists are talking don’t also contain hums and other background noise. Even when someone’s talking, there are natural pauses through which the hums and noise can bleed through. If I can remove them from everybody’s audio track, you won’t get distracted when the character of the audio changes dramatically every time someone else starts talking.

The screen shots from iZotope RX 5 are fun, but hearing is believing: Here’s a section of that track from David Loehr, before and after I removed the hum and noise.

I mentioned above that iZotope RX 5 also includes a de-reverb effect. That’s actually the primary reason I upgraded to iZotope from SoundSoap—some of my panelists have very echoey recording spaces. In time, perhaps they’ll change their recording set-up and it won’t be a problem, but I’d like to be able to suppress as much room echo as I can in the meantime.

Musicians add reverb to tracks all the time, but the idea of removing reverb seems kind of crazy. In fact, it requires a whole lot of wacky mathematical modeling of sound decay at various frequencies. But you know what? When it works, it’s magical.

This Christmas, my friend James Thomson joined me (and David Loehr!) for a podcast about the “Doctor Who” Christmas Special. James couldn’t use his usual recording location, however, because his mother-in-law was in town and was sleeping in that room. So he recorded from his kitchen, which was not the ideal recording location. It was a bit echoey.

If you’d like to hear how James’s original audio sounded like, what it sounded like after de-reverbing, and then what it sounded like with de-noising added, here’s a sample file.

Should aspiring podcasters run out and spend several hundred dollars for professional audio software? No. Start with Audacity or, if you’re using Audition, the built-in de-noising features. But if you’re interested in taking the next step—or you’ve got some brutal audio that you need to improve—you’d be surprised at the quality of the results you can get with a little bit of time and some clever software.

[If you appreciate articles like this one, help us continue doing Six Colors (and get some fun benefits) by becoming a Six Colors subscriber.]

[Don't miss all our podcasting articles.]