Post-processing

Sound for Video Session: Order of Operations - Processing Dialogue Audio

In this week's sound for video session, we cover my thoughts on which order I apply each effect or process when cleaning and sweetening dialogue audio.

This episode shot/recorded with:

Sennheiser EW112 G3 Wireless Microphone Kit (be sure to check which frequencies you are legally allowed to use in your country)

Voice Technologies VT Duplex Headset Microphone

Panasonic GH5 Camera

Panasonic 12-35mm f/2.8 Lens

Copyright 2017 by Curtis Judd

Free Audio Plugin Voxengo SPAN for Post Processing Sound

One of the most important tools for post-processing audio is a spectrum analyzer. In this episode, we discuss a free spectrum analyzer plugin for almost all digital audio workstation apps called Voxengo SPAN.

Even if you’re just starting out processing your audio, a spectrum analyzer like SPAN will not only teach you a lot about how sound works, but will also help you to solve practical issues and make processing decisions. We introduce the idea of multi-band compression and illustrate how SPAN can help you decide where you set the boundaries for the different bands.

The end result? Audio processing that improves the quality of your recorded dialgoue.

Because you sometimes ask, the voiceover in this was recorded with the Electrovoice RE20 microphone and the audio we show in Audition was recorded with an Audio Technica AT4053b Hyper-cardioid microphone and recorded with a Sound Devices 633 mixer/recorder.

Dialogue Audio Compression (Slightly More In-depth)

Still have a lot to learn but feels like we've turned a corner and are getting better sounding results for my video projects.

Compression of dialogue audio requires a bit of finesse to be effective. While learning, I've sometimes ended up with over compressed audio sounding something like this: Audio clip with a regular clip control law compressor

So first, why compress dialogue audio? So that the purpose of your film or video is served. The audio should help tell your story without making it hard for your audience. It allows you to loudness normalize to the established broadcast standards or recommendations so your audience doesn't strain to hear or experience the pain of audio that is too loud or distorted. For those that will watch or listen on mobile devices with earbuds, they can hear your project clearly.

We've covered audio compression in previous episodes but kept the description super simple as a start. That approach is a good intro but sometimes it doesn't work out very well and your audio ends up sounding over-compressed, sort of crushed and un-natural. So in this episode, let's look at a couple of things you can do to prevent that crushed sound.

First, check to see if you even need to compress your clip. Most of my footage needs just a little bit of compression so that I can loudness normalize for mobile and computer viewing. In audition, loudness normalize and see if your peaks get clipped. If not, no need to compress.

Compression graph: Axes = input level and output level and threshold

First and most obvious thing: Don't use a crazy compression ratio. There's no way it will sound natural. I like to stick to 2:1 per pass.

There's still a potential problem: Compression is applied in a pretty abrupt fashion, right at the threshold

One solution: Soft knee where the compression is applied more gently over a span of amplitudes (dBs, or loudness levels). And this can result in a more natural sound.

Unfortunately, Audition doesn't come with a compressor plugin that has a soft knee feature. Adobe, that'd be a really nice addition. :)

However, Audition supports VST plugins (or on Mac, both VST and AU). Here I'm using Izotope's Ozone 6 "Dynamics" plugin which is a really nice, though somewhat expensive option just to demonstrate how it works. There are gazillions of other options out there, some free, others at a price. If you have a favorite compressor plugin with a soft knee and an RMS "control law", let us know in the comments below! I've also included a link to one or two free options.

Speaking of "control law", what is a control law? This is how the compressor knows when to start compressing. Most compressors work based on peak control. They watch for peaks that hit or exceed the threshold and then start compressing. However, another option is an RMS control law. Without making the explanation too complex, this is essentially a way to average out the signal so that the compression starts its work in a more natural way--its isn't so fidgetty. This can also help to keep the dialogue sounding more natural vs. a peak based compressor.

Attack - how long the compressor waits after the waveform has exceed the threshold before it begins reducing the amplitude (or volume in laymen's terms). For dialogue, I keep this quite short, 20 ms or less, often right at 0 to 5 ms. We keep this short because we don't want too much of the peaks getting through since we are trying to loudness normalize.

Release - how quickly after the waveform has gone back under the threshold that the compressor stops reducing amplitude. I often set this between 80 and 150 ms. If you set too short a time, you'll bet a pumping sort of sound, and if set too long, you'll compress everything. Fancier compressors have an auto release which tracks the waveform and releases at the right time adaptively.

Then we loudness normalize and set to go!

DaVinci Resolve: Quick White Balance Correction with RGB Curves

Have you ever forgotten to set your white balance when shooting video?  Or have you downloaded your footage and realized that the color was a little, or even a lot, off? You can fix it quickly and easily in DaVinci Resolve with the RGB curves. And the same idea applies to any color grading app with RGB curves.

Now don’t let that scare you off. I used to be scared of the RGB curves. They seemed so complex and mysterious. But using this simple method, you can white balance a clip in just a few seconds!

I learned how to do this from Alex over at the new YouTube channel “Learn Color Grading”. Lots of quality tutorials on color grading with DaVinci Resolve, definitely worth your time to have a look and subscribe: https://www.youtube.com/user/LearnColorGrading

Here are a couple of tools I use to ensure I can correct my white balance in post:

X-Rite ColorChecker Passport is a little pricey but is a professional tool with not only a white balance patch, but also standard color chips that allow you to put the ColorMatch feature in DaVinci Resolve to use - an automated way to color balance your footage.

Lastolite Ezy Balance Gray/White Card is a little less pricey and is a great, durable, foldable card you can use to white balance your footage in post, set a custom white balance in your camera, manually set your exposure, or manually focus. Great tool. I've had mine for probably 4 years now and I use it all the time.

Audio Drift: How to Prevent It or Fix It with Audition

http://youtu.be/lLQOyaYkhkA When you record your audio on a separate recorder from your video, sometimes you can experience audio drift. This is where you sync up the start of the video clip to the start of the audio clip but over time, the audio becomes more and more out of sync with the video. This can be incredibly frustrating and you may even have to reshoot.

In this episode we’ll talk about some things you might do to prevent this issue in the first place (hint: smart phones tend to experience this issue more than other cameras, be sure to set your sample rate on your audio recorder so that it matches the camera’s audio sample rate). And if all that fails, here’s a tool in Adobe Audition called Automatic Speech Alignment that might be able to solve this problem for your drifting audio.

Fixing Sound That Only Plays In One Speaker

One question that I get quite often is, “My recorded sound is only coming out of one speaker. How do I fix that?” This is usually a result of recording a mono mic into a stereo recorder or camera. The fix is very simple in Adobe Audition and most other audio editing apps (like Audacity which is free). This same fix also applies to cases where you recorded two mics into a recorder and one mic only comes out of one speaker, and the other mic only comes out of the other speaker. http://youtu.be/BKepIceNf1M