Real-Time Audio Mixing in Final Cut Pro

Final Cut Pro can mix and play back multiple audio tracks in a sequence in real time, even while you make adjustments to levels, stereo pan, and audio filters. The number of tracks that can be played back depends on the number of filters applied to your clips and your computer’s capabilities and settings, including:

Different filters and transitions affect real-time playback to varying degrees. If Final Cut Pro can’t mix all the tracks in a sequence in real time, you hear a series of beeps indicating that part or all of your sequence must be rendered before being output as a final mix.

Tip: You can turn these beeps off by deselecting the Beep When Playing Unrendered Audio checkbox in the Playback Control tab of the System Settings window.

Calculating the Number of Tracks That Can Be Played Back in Real Time

The number of tracks Final Cut Pro attempts to mix in real time is determined by the Real-time Audio Mixing setting in the General tab of the User Preferences window. The number of tracks you can play back in real time is largely dependent upon your hardware, so performance will vary from system to system. Increasing the number of tracks in this field doesn’t mean they’ll all play.

Important: If the number of tracks is set too high, you may have dropped frames during playback.

To determine the number of tracks your system can play back in real time
  1. Add a video clip with a typical data rate for your working environment to your sequence.

  2. Add 16 or more audio clips at the same point in time as your video clip.

  3. Choose Final Cut Pro > User Preferences, then click the General tab.

  4. In the Real-time Audio Mixing field, enter the number of tracks in the sequence.

  5. Make sure the “Report dropped frames during playback” checkbox is selected.

  6. Click OK.

  7. Play back the sequence.

    If your system cannot perform real-time playback of the number of tracks in the sequence, you see a “dropped frames” message.

  8. If you have dropped frames, reduce the number of tracks in the sequence and play it back again. Repeat this step until the sequence plays without dropped frames.

  9. Set the number of tracks for the Real-time Audio Mixing option in the General tab of the User Preferences window to the number that played back without dropped frames.

Improving Real-Time Audio Performance

You can optimize real-time audio performance in the following ways:

  • Render video effects prior to mixing: Playing real-time video effects reduces the number of audio tracks that can be mixed in real time. While mixing the audio in your program, you can maximize real-time mixing performance by first rendering all video effects in your sequence, including all transitions, layered video, and filters. Video and audio render files are maintained separately, and changes made to the audio levels in your sequence do not affect the video effects that have already been rendered. For more information on rendering the video effects in a sequence, see Rendering and Video Processing Settings.
  • Render audio filters: Even though many audio filters play in real time, unrendered filters can reduce the number of tracks you can mix in real time. The number of audio tracks you can play without rendering depends on how many filters are applied and how many audio tracks you’re trying to mix at once.

    To increase the number of audio tracks that can be mixed in real time in sequences with audio filters applied, you can perform item-level rendering on individual audio items in the Timeline. By rendering audio items with filters individually, audio and pan levels can continue to be mixed in real time, and you can make level changes without rerendering. For more information, see More About Audio Render Options and Rendering Audio Items in a Sequence.

  • Use the Mixdown command to prevent dropped frames: If you have a complex audio mix with numerous clips, keyframes, filters, and transitions, the mix may start to affect the playback of your sequence. Also, if the Audio Playback Quality setting in the General tab of the User Preferences window is set to High, you may get dropped frames in your audio. You can use the Mixdown command in the Sequence menu (available by choosing Sequence > Render Only > Mixdown) to render all the audio tracks in a sequence, along with their accompanying transitions and filters, into a single render file. For more information, see Using the Mixdown Command.