Better Audio Mixing for Commentary Videos [Audacity]

Discussion in 'Video Encoding' started by Rensje, Sep 20, 2012.

  1. Rensje

    Rensje Site Contributor Well-Known Member

    Reading a recent help request topic on these forums inspired me to do a short tutorial on audio mixing, because it is an issue that I struggled with myself before I found a really great and easy solution! Better still, all the software that we will be using in this guide is free, so you definitely need not invest loads of cash to achieve great results.

    To keep this guide concise, I am going to assume you know how to record gameplay and sound with Fraps. We will just be focusing on how to set up and use our audio and video software for the purpose of mixing game sound and commentary effectively.

    STEP 1 - Getting Started:
    • Download and install Audacity anywhere on your computer. Audacity is a free, easy-to-use and multilingual audio editor and recorder. We will be using it to record our commentary with, and to do the actual audio mixing.
    • Download and install VirtualDub. VirtualDub is a video capture/processing utility licensed under the GNU General Public License (GPL). We will use it to edit and encode our video.
    Once you have the proper software installed, it is time to prepare a video for this guide. It does not matter whether you record your commentary live or in post, both methods will work just fine.

    STEP 2 - Setting up Audacity:
    • Open Audacity.
    • Click Edit > Preferences...
    • In the Devices tab, set Channels to 'Mono'.
    This is to make sure your voice is recorded to a single audio track, which is easier to work with.
    • At the bottom of the Audacity screen, set Project Rate (Hz) to '44100'.
    Now record your commentary. You can either do it live, or in post. If you do it live, not that Audacity has to be the prioritised window in order to be able to start the recording.

    Your Audacity window should now look something like this:


    For now, we will save our commentary track and close it. We will come back to it later. To save, click File > Export... and save your track anywhere on your computer. Give it a name that is easy to distinguish, something like 'video1_commentary_raw'.

    STEP 3 - Extracting game audio from your video:
    • Open VirtualDub.
    • Drag your video into the VirtualDub screen, or go File > Open Video File...
    • Click File > Save WAV... and make sure you give it a simple name, something like 'video1_gameplay_raw'.
    Now we have both the gameplay audio and the commentary saved as audio tracks, we can start the actual mixing.

    STEP 4 - Prepping the commentary:
    • Open Audacity.
    • Click File > Open... and find 'video1_commentary_raw'. Open it.
    Your Audacity window should now, again, look something like this:

    • Click Effect > Compressor... and click Okay, using the following settings:

    You will notice that the audio track looks a lot louder now. And it is. We do this to bring the sound level of the commentary track up to the same level as the game audio, regardless of how loud or quiet it was before.

    Now let's work on noise removal.
    • With the selection tool, click and drag to mark a section of the audio track that is just noise, like so:
    • Click Effect > Noise Removal... > Get Noise Profile.
    • Make sure you select the entire track (CTRL+A).
    • Click Effect > Noise Removal... > Ok, using default settings. Make sure Noise is set to 'remove' and not 'isolate'.
    This basically tells Audacity what you consider to be noise, and which parts are safe to remove. It is a fairly fool-proof method and nothing essential will be deleted from your commentary track.

    In case any unwanted sounds are left over, select them with the selection tool and press CTRL+L (Silence Audio). You can always undo changes if you make a mistake.

    Now that we have an audible and clean commentary track, it's time to bring in the game's audio and start the magic.

    STEP 5 - Prepping the game audio:
    • Click File > Import > Audio... and find 'video1_gameplay_raw'.
    This will open the game audio in the same window as the commentary track. It will appear below the commentary track, but we want it to appear at the top.
    • Click and hold anywhere in the empty grey space at the left of the game audio track, and drag it to the top. You can tell which track is selected by the yellow border surrounding it.
    The Audacity window should now look something like this:


    Make sure that JUST the game audio track is selected for the next few steps!
    • Click Effect > Compressor... and click Okay, this time using -35dB for Threshold and 5:1 for Ratio.
    Now both the game audio and commentary are about equally loud, but that still makes it hard for you to hear the commentary over the game. Let's fix that. With the game audio track still selected:
    • Click Effect > Amplify...
    • Set Amplification (dB) to approximately -15dB and click Okay.
    • Click Play to try out whether the commentary is now clearly audible over the game sound.
    -15dB is a good starting point, but you can play with the Amplification (dB) setting until you get it to sound exactly how you want to. Just make sure you undo previous amplifications before you apply the effect again, or else your game audio will be doubly quiet.

    One last thing to do before we make the actual sound mix. Make sure just the game audio track is selected.
    • Click Effect > Auto Duck... and click Okay, using these settings:

    What this does is make the game audio a little bit quieter every time you are speaking, and return it to normal volume when you are not. This way the viewer (and therefore listener) can hear you speak easily and still enjoy the sound of the game as it was intended.

    STEP 6 - Mixing and Saving:
    • Click Tracks > Mix and Render
    This will mix down your two seperate audio tracks into one final stereo track. All that is left now is to export it!
    • Click File > Export... and save the file with a name like 'video1_gameplay_commentary_final'.
    That's it, you are done. The audio mixing is complete. Now we need to reunite the audio with the video!

    STEP 7 - Encoding
    • Open VirtualDub.
    • Click File > Open Video File... and find your original video.
    • Click Audio > Audio From Other File... and find 'video1_gameplay_commentary_final'.
    There you go! Play the video back in VirtualDub to see what it looks and sounds like as a result! The actual encoding of the video in VirtualDub is beyond the scope of this tutorial, but an excellent guide by raffriff can be found here.

    I hope you found this guide helpful and informative. As a final treat, here is a sample video I made by following the exact steps in the guide above:

  2. As a final treat, here is a sample video I made by following the exact steps in the guide above:
    "This video does not exist."

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