Audio Compression Basics
An audio compressor reduces the dynamic range of your audio. It makes the really loud parts a bit softer and the really soft parts a bit louder. It “compresses” the peaks and valleys so that everything is more even.
When used properly, audio compression can really help a voice-over consistently stand out from the background or give a bass guitar “punch” in the mix of a song. As with almost all effects, you should use compression sparingly. Use just enough to achieve the desired effect; too much compression will probably make the audio sound like it’s “pumping” or “breathing.” Also, be aware that if you have background noise on a track, compression may make the noise louder. You may want to perform noise reduction (as described in the February 2009 Sony Vegas Tips & Tricks) prior to adding compression.
Compression ratios are described as “2 to 1” or “10 to 1” and written as 2:1 or 10:1. A 2:1 audio compression ratio means that for every 2 decibels of input, the compressor will output 1 decibel. The threshold indicates when the compression begins to take effect.
A compressor (Figure 1, below) is one of the three FX present in all audio tracks by default. To use a compressor on an audio track in Vegas, do the following:
1. Select and Loop a section of audio in the audio track.
2. Click on the Track FX button of your audio track. This brings up the Audio FX chain.
3. Choose the Compressor whose check box should be checked by default.
Compression for Voiceovers
For voiceovers, a setting of 2:1 or 3:1 is good to start with. If you’ve installed an add-on such as US Pro, you will have even more presets to choose from, and you can always tweak the settings and save your own reusable presets.
Play back the looped selection so you can hear how the compression affects the audio in real time. It may help to solo the track you are working on (by clicking the exclamation point on the track header) to get the settings right, and be sure to listen to it mixed with the other audio tracks for a true representation of the sound. Oftentimes, you can apply compression and then raise the overall volume of the entire track to help set it apart from the background (Figure 2, below).
Rendering AC-3 Files for DVD Architect
Here’s an audio tip for encoding files in Vegas for use in Sony DVD Architect. You always want to encode two separate files: one MPEG-2 file for video and one AC-3 file for audio. For some reason, Sony continues to ship the AC-3 encoder set to defaults that will alter the audio levels. Many users don’t know this. So they wonder why their audio sounds and meters fine in Vegas but is too loud once they’ve prepared and burned their DVD in DVD Architect. Here’s all you need to do to create a custom template to use anytime you encode AC-3 audio (Figure 3, below):
1. Choose File > Render As.
2. Choose Dolby Digital AC-3 Pro. Default Template should be selected.
3. Click Custom. On the Audio Service tab, and set Dialog Normalization to -31 dB.
4. Click the Preprocessing tab. Set both Line mode profile and RF profile to None.
5. Save this new custom preset by typing a new name directly over the Default Template name and clicking the disk icon to save it.
Using these settings will prevent the AC-3 encoder from changing your audio levels from what you hear while you’re editing in Vegas.
UltimateS Pro Audio Tips
Do you want to instantly make your voiceovers sound better? UltimateS Pro 4 (Figure 4, below) is the latest version of the highly popular scripting tool from VASST.com. I am such a fan of this Vegas add-on that I can’t pretend to be neutral about it. It contains 15 tabs chock-full of useful stuff, but right now we’re talking about audio. US Pro makes getting a “good” audio sound as easy as a couple of clicks. Vegas has chained together a series of custom presets as well as incorporated an audio engine from iZotope. Here’s what we do to every groom or officiant mic we record with:
1. Select the track or tracks containing the audio (from a mic’d groom, for instance).
2. Click on the UltimateS Pro 4 tab. Users of older versions of UltimateS will open the tool from the scripting menu.
3. Click Enable Audio FX and choose the preset Male Voice Over. Click Apply.
That’s all there is to it. US Pro puts custom compression and EQ curves on your selected tracks. There are other presets to choose too, but Male Voice Over and Female Voice Over get used an awful lot in our shop.
UltimateS Pro 4 includes literally hundreds of useful scripts and tools covering all areas of Vegas; this is just one of my most-used audio tips.
That’s all for this month. Thank you for reading and thanks to those of you who have emailed with questions or comments just letting me know you like the columns. I’ll see you in Vegas!
David McKnight (david at mcknightvideo.com) is half of McKnight Video of Houston. He is vice president of the Houston Professional Videographers Association, has Sony Vegas and HDV certification, is the technical editor of Vegas Pro 8 Editing Workshop (Focal Press), and is a contributor to TheFullHD Book (VASST). He and his wife, Christie, are winners of multiple HPVA awards.