FCP X: The Limiter Filter
If you are interested in improving your audio, Final Cut Pro X made several huge steps forward by incorporating all the Logic/Soundtrack Pro audio filters with the application. Because I principally create programs which are driven by audio – what is being said – rather than action, it is essential to me that viewers are able to clearly hear the dialog.
This means that a filter that before FCP X was only available in Soundtrack Pro, is now part of the audio effects suite in FCP X. It’s called the Limiter filter and I want to show you how to use it. The purpose of the Limiter filter is to make soft audio louder while preventing the louder passages from distorting (which happens when audio levels exceed 0 dB). In fact, when used properly, the Limiter Filter virtually guarantees that your audio won’t distort.
What the Limiter filter does – on an instant-by-instant basis – is raise the level of that instant of the clip by an amount you specify, provided the audio level doesn’t go over a maximum limit that you also specify. Audio gain that attempts to go over your limit is thrown-away.
The three key settings in the Limiter filter are: Gain, Gain Reduction, and Output Level.
The last time I wrote about setting levels I got severely taken to task by an audio engineer complaining that my numbers were all wrong. So there are five things you need to understand:
- FCP X displays audio levels as peaks using the dBFS scale. FCP X does not display RMS, or average, audio levels. Therefore, all my recommendations about audio levels are based on the peak settings displayed in FCP X.
- FCP X does not display PPM levels, which are used extensively in Europe.
- The levels I share with you here are perfect for the web, most DVDs, and many cable and broadcast programs. However, for feature films, or audio situations requiring RMS measurements, these guidelines are not appropriate. The Limiter filter can still be used in these situations, just not with these settings.
- In audio, just as in video editing, every rule has exceptions. Consider this article as guidance, not “truth carved in stone.”
- It could be argued that a Compression filter would create the same results as the Limiter filter. While true, I find the Limiter filter easier to teach and faster to adjust, while delivering the same results as a compression filter without excessive tweaking or requiring that the user to understand how a compressor works. The “Soft Knee” in this filter makes the transition to compression especially useful.
WHERE TO APPLY THE FILTER
The Limiter filter works best when it is applied to dialog and narration, not sound effects or music. This means that you need to be selective about where you apply the filter. (I strongly discourage using the Limiter filter for music.)
In general, audio effects in FCP X are applied to the clip. However, in the case of the Limiter filter, it may be a better idea to make a compound clip of all your dialog clips. This allows you to apply one filter to a group of clips, which makes adjustments a lot easier. All clips in a compound clip do not need to be next to each other. Here’s an article that explains this more.)
NOTE: For really complex mixes, you are always better moving your audio out of FCP X into ProTools or Adobe Audition or Soundtrack Pro because they can deal with applying filters to multiple layers of audio clips better than FCP X can.
Here is a set of of four Soundtrack Pro tutorials that can help you improve your audio.
APPLYING THE FILTER
Whether you apply this to a compound clip, a collection of individual clips, or just one clip, the process and adjustment is the same.
1. Select the clip(s) to which you want to apply the filter. In this case, I’m applying the filter to a compound clip.
2. Open the Effects Browser (type Command+5) and select the Audio > Levels category. Scroll down the list of filters on the right side until you find the Limiter filter. (While there are a number of settings files in that category, most are simply presets derived from the Limiter filter.)
3. Drag and drop the Limiter filter on top of the clips to which you want to apply it. (Or, if all the clips are selected, simply double-click the Limiter filter to apply it to all selected clips.)
NOTE: To remove the filter, select all the clips that contain the filter you want to remove, go to the Inspector, select the name of the filter, and press Delete.
ADJUSTING THE FILTER
1. Select the clip(s) that contain the filter.
2. Open the Inspector (type Command+4) and click the Audio tab at the top. The Limiter filter is displayed at the top of the Inspector.
3. Click the small icon to the right (its under the cursor in this screen shot) to open the Limiter interface.
4. For all dialog and narration, I recommend setting the Limiter to the following settings:
- Output Level: -4.5 dB
- Release: 300 ms or larger
- Lookahead: 2 ms, which is the default setting
- Soft knee: On (the square button glows blue, which is the default)
As audio levels are additive, setting the Limiter to -4.5 dB means that you have room in your mix to add sound effects and music, while still able to hear dialog. On tracks which are narration-only with no other audio in the mix, I will increase the Output Level to -3 dB. However, currently, I tend to set everything at -4.5 dB.
5. Here’s the one setting you need to adjust: Gain. This setting varies each time you apply the filter. Start by playing your clip. Slowly increase the Gain slider until you start to see small blue bars at the right edge of the Gain Reduction display at the top. Continue increasing the slider until you are throwing away 1 – 3 dB of gain during the loudest portions of the audio. Levels displayed in the Gain Reduction slider is audio level that would normally exceed the Output Level, but is caught by the Limiter.
This filter has the effect of increasing the softer passages of your audio while making sure neither the louder passages, nor the amplified passages of your clip are louder than the Output Level. This prevents distortion (audio levels that exceed 0 dB) while making your entire clip MUCH easier to hear by leveling out audio levels.
In this example, I am raising the audio of the entire clip by 16.5 dB, however, the Output Level guarantees that at NO TIME do any of the audio peaks in the audio exceed -4.5 dB. (Every clip’s settings will be different, this specific number applies only to this example.)
NOTE: This filter is especially good at leveling out audio with lots of pops, clicks, or extreme level changes.
I find this filter indispensable in my mixes. And, once you start using the Limiter filter, I suspect you’ll wonder how you lived without it.
IMPORTANT NOTE: If you assign multiple audio filters to a clip which has the Limiter filter applied, make sure that the Limiter filter is applied LAST. It should always be at the bottom of the list of audio filters in the Inspector. Otherwise, you lose its ability to prevent audio distortion.
To change the stacking order of audio filters, drag their names up or down in the Inspector.