I use Compressor to export my FCPX project to h264 .mp4 files.

Playing the file I exported today, the audio quality was bad (sounds muffled). This problem appears only in the output via Compressor.

  • Playing on the FCPX timeline -> OK
  • Playing the output exported via "Share" feature and "Apple Devices 720p" setting -> OK
  • Playing the output exported via Compressor -> NG

There were no problem two months ago. I don't make any changes in the export settings.

Any ideas or solutions?


  • Mac OS X 10.9.5 (Marvericks)
  • Final Cut Pro X 10.1.4
  • Compressor 4.1.3

Setting of Compressor


Output of ffprobe

audio of previous output (good quality)

Stream #0:0(jpn): Audio: aac (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 63 kb/s (default) Metadata: creation_time : 2014-11-29 10:42:07 handler_name : Core Media Audio

audio track of this time output (bad quality)

Stream #0:0(jpn): Audio: aac (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 44 kb/s (default) Metadata: creation_time : 2015-02-07 14:28:54 handler_name : Core Media Audio

Looking at bitrate above, it's less than one of the previous output. I retried the encoding with setting the audio bitrate to 128kbps.

Stream #0:0(jpn): Audio: aac (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 86 kb/s (default) Metadata: creation_time : 2015-02-07 13:15:43 handler_name : Core Media Audio

However the problem was not solved.

  • 1
    I notice you're exporting as mono. Is the source track mono? Sometimes when you blend two stereo tracks into mono they can interfere if the two channels are out of phase, which can cause a muffled sound. Try deleting one channel or inverting the phase and see if that helps.
    – stib
    Feb 8, 2015 at 2:01
  • @stib Thanks. The FCPX project allows either of Stereo or Surround as the audio channels configuration. (I choose Stereo in this case.) So tried two solutions. 1) I checked the "Channel Configuration" of "Audio" inspector and check only one mono track. 2) Change the export setting to stereo. However neither of them solved this issue.
    – kaorukobo
    Feb 10, 2015 at 8:06

1 Answer 1

  1. FCPX project -> Play through timeline = OK
  2. FCPX project -> Compressor -> ProRes422 = NG (muffled sound)
  3. FCPX project -> Compressor -> AAC Mono = NG (muffled sound)
  4. FCPX project -> Compressor -> AAC Stereo = NG (muffled sound)
  5. FCPX project -> "Share" -> Master (h264) = OK (but the size is too large)
  6. FCPX project -> "Share" -> Master (h264) -> Compressor -> AAC Mono = OK

These are sum-up of results in my trial and error. The 6th trial resolved my problem, although it is not a perfect solution.

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