Final Cut Pro: Setting Real-Time Audio Mixing Tracks Preference

The Real-time Audio Mixing setting in the General Preferences tab (see Figure 1) defines how many audio tracks Final Cut Pro attempts to mix without rendering. If too many tracks are set, video playback performance may suffer. If too few tracks are set, Final Cut Pro renders audio prior to playback when more audio tracks are used in an edit than are specified.

Figure 1 Real-time Audio Mixing setting in the General Preferences tab
The maximum number of tracks you can enter into this field varies depending on CPU speed and type, hard disk performance, available memory, and other factors. To determine the maximum number of audio tracks that will play along to video without having to render, follow these steps:

1. Create a new project. Import one video clip and one audio clip.

2. Set the Real-Time Audio Mixing field of the General Preferences tab to a deliberately high number, such as 16. This is to prevent Final Cut Pro from making any assumptions about what can be played back without rendering. Also, be sure to enable the Report Dropped Frames option in the Capture Preferences tab.

3. Edit the video and audio clip into the timeline of Sequence 1, occupying the same area of the timeline.

4. Now, a track at a time, edit additional clips of audio into additional audio tracks so that they overlap the previously edited material, and play them back. As long as Final Cut Pro does not report any dropped frames, continue adding tracks.

5. As soon as a dropped frame is reported, you know that you are one track over the maximum number of tracks that you can enter into the Real-Time Audio Mixing field.

Adding audio filters and mixing levels reduces the number of tracks that play back without rendering. In these cases, it may be prudent to lower the number specified in the Real-Time Audio Mixing field to prevent inconsistencies during playback.

In cases where there are perhaps too many tracks or effects applied to allow for real-time audio mixing, the Mixdown Audio command (see Figure 2) forces Final Cut Pro to render all audio tracks in order to optimize playback performance. Using this command does not result in all tracks being destructively mixed into one track in the Timeline. It simply refers to the process of all tracks being rendered to cache files in advance of playback.

Figure 2 Mixdown Audio menu item

Note: If you have complex multi-layered audio and want to recut your visuals without constantly re-rendering, please see article 31218: "Final Cut Pro: Avoiding Rendering of Audio Clips When Using Filters"