How to Stereoize Mono Sounds: A Trick for Creating Acoustically Sound Clips

2015/02/25

Stereoize Hero

Have you ever returned to your edit suite to realize one channel of your stereo field recordings is distorted beyond hope? Has a client demanded a stereo delivery spec, regardless of the source sound effects in your sound library? Do you have a cool mono drone you’d like thicken up?

If any of these situations sound familiar, you’ve likely thought about transforming your mono sounds into a stereo file.

However, this task of “stereoizing” mono files isn’t simple. Why? Well, there’s the ever-present risk of accidentally corrupting your new stereo file with phase problems. And what about audio quality? Often stereoized files sound flat and lifeless. Is it possible for stereoized mono files to sound good?

I struggled with this for years. I used mastering hacks to get this done: shifting a duplicate track a few frames, or dropping half of a mono clip underneath on a second track. There are other tricks. I wasn’t satisfied with any of them.

A few years ago I stumbled across a post that explained a bulletproof, acoustically sound method of stereoizing a mono file. It recreates the physics behind the way our ears hear sound.

I tried it. I was thrilled with the results. I’ve used it ever since.

Today’s post is the first in a two-part series that explains how to use this trick. This article shares step-by-step instructions for stereoizing mono files, with the kind assistance of a special guest contributor.

About the Stereoizing Trick

As I mentioned, today’s steroizing trick is not my own. The trick was posted years ago by Shaun Farley in a thread on Social Sound Design.

Shaun Farley

Shaun Farley

Many of you know Shaun Farley. In addition to performing editing duties, Farley is a contributing editor at popular pro audio news site Designing Sound, as well as an active member of the sound design and field recording communities. He also shares his field recording bundles in his sound shop.

Shaun kindly helped me share his stereozing trick in today’s post. So, today’s article explains the nuts and bolts of the trick. It describes how to set up your session and capture acoustically sound stereoized audio files. It lays out step-by-step instructions to get the job done quickly.

Next week expands upon the topic of stereoizing sound files with a special treat: Shaun Farley will explain how he discovered the trick, why he uses it, its benefits and risks, and more. Don’t miss it. It’s a goldmine of info that cements the trick in sound theory.

Let’s get to the trick. I use examples and screenshots from Avid’s Pro Tools, however it can be adapted to any other audio editing app with a bit of effort.

How to Stereoize Mono Files

Prep the Session

  1. Create a new blank session.

  2. Add two mono tracks. These will store your source mono files. (Click the image below for a large version of the screenshot.)

    How to Stereoize - Add mono tracks

    Add mono tracks

  3. Add two mono aux tracks. These will handle the plug-in processing and additional audio routing.

    How to Stereoize 2 - Add aux tracks

    Add aux tracks

  4. Add a stereo master fader. This is where you’ll monitor your work.

    How to Stereoize - Add a master fader

    Add a master fader

  5. Add a stereo track. This is where your final, destination audio will be captured.

     Add a destination track

    Add a destination track

Add the Audio

  1. Add your mono audio clip to track 1. In this case, I’m using an old mono room tone.

    Add a clip

    Add a clip

  2. Add an edit in the middle of the track. This will create two regions.

    Create an edit

    Create an edit

  3. Drag the second region beneath the first.

  4. Trim the clips so they start and end at the same time. Add fades if you like.

    Trim the clip

    Trim the clip

Add Plug-Ins

  1. Add your favourite stereo monitoring plug-ins to the master fader. This will help you keep an eye on the stereo field and correlation. In this case, I have added my two favourite stereo analysis plug-ins: Inspector XL’s Stereo Analyzer, and iZotope’s Insight.

  2. Add the “Short Delay” plug-in to each aux track. Every version of Pro Tools will include this plug-in.

    Add aux plug-ins

    Add aux plug-ins

  3. Set the delay time for each track’s plug-in. Note: the delay times on either track must fall within the range of 10–30 milliseconds. This accurately emulates how our ears hear. (Shaun Farley will explain more about the science behind this in next week’s post.)

    For example, in my session, I set the delay for the first aux at 15 milliseconds, and the second aux track’s delay to 30 milliseconds. Both of these times safely fit within the 10–30 millisecond range.

    Delay plug-in settings

    Delay plug-in settings

Configure the Mix Desk

Set Up The Mono Source Tracks

Set up the “left” mono source track:

  1. Create a send on the first mono track directing it to the the first aux track. For this example, we’ll send it to bus 9.

    Set the mono #1 send

    Set the mono #1 send

  2. Adjust the level of the first send (it will be created at ∞).

    Set mono #1 send level

    Set mono #1 send level

  3. Set the output of the first mono track, directing it to the left side of your stereo “destination” track. In the case, we’ll choose bus 19.

    Set mono #1 bus out

    Set mono #1 bus out

Set up the “right” mono source track:

  1. Do the same for the second source mono track send: direct it to the second aux track. We’ll use bus 10 for this.

    Set the mono #2 send

    Set the mono #2 send

  2. Adjust the level of the second send (it will be created at ∞).

    Set mono #2 send level

    Set mono #2 send level

  3. Set the output of the second mono track, directing it to the right side of your stereo “destination” track. In the case, we’ll choose bus 20.

    Set mono #2 bus out

    Set mono #2 bus out

Set Up The Aux Tracks

Set up the “left” mono aux track:

  1. Configure the input on aux 1 to receive the send from the left mono source track, above. So, the input should be from bus 9.

  2. Set the output of aux 1 to direct it to the right side of the “destination” track, which is bus 20. We send it to the opposite channel to create the delayed, “natural bleed” in the opposite ear.

  3. Set aux #1 routing

    Set aux #1 routing

Set up the “right” mono aux track:

  1. Configure the input on the second aux track so it receives the right mono source track. So, the input should be bus 10.

  2. Set the output of aux 2 to direct it to the left side of the “destination” track, which is bus 19. Again, we send it to the opposite channel to create the “natural bleed” in the opposite ear.

  3. Set aux #2 routing

    Set aux #2 routing

  4. Finally, diminish the level of both the aux track channels. They must be lower than the level of the source mono tracks. Note: lower levels here will create a wider stereo image, and higher levels will create a narrow image.

    Diminish aux levels

    Diminish aux levels

The Stereo Destination Track
  1. Set the input of the stereo destination track to bus 19 & 20. This will receive the audio from the mono source tracks. It will also receive the delayed and swapped audio from the aux tracks.

    Destination input settings

    Destination input settings

  2. Place the destination track into record.

    Destination, record ready

    Destination, record ready

Here’s a screenshot of the entire workspace (it’s pretty big):

The entire editing workspace

The entire editing workspace

Creating Stereoized Mono Files

  1. Select your mono file.

    Select the mono file

    Select the mono file

  2. Type command-space. This will play the region and record a bounced copy. It combines the source mono tracks with a delayed, swapped, and quieter copy from the aux tracks, then dumps everything together into the destination track.

    Note:

    • Watch the stereo monitoring tool on your master fader to keep an eye out for phase problems.
    • Your tracks may peak. If so, adjust your levels to compensate.

And that’s it! If you’ve followed the steps with care, you’ll have created an acoustically sound stereo file from a single mono file.

Tip: Planning on stereoizing a few mono files? Set up the session and save it as a session template.

A special thanks to Shaun Farley for his generous assistance ironing out the details of this post.

Understanding How the Trick Works

Today’s post was designed to share a quick step-by-step guide to creating stereoized sound effect tracks.

Why should you use this method? How does it work? Why is it better than others? Join me in next week’s article where Shaun Farley answers these questions, and more.

Follow me on Twitter or join the free email newsletter. I’ll announce when the next article is ready.





To stay in touch, receive free updates by email newsletter or RSS feed.  |  Follow on SoundCloud