Q: Audio drop-out in FCPX with 1920x1080 & 2048x1240p @ 24p (codec Apple ProRes 4444 (Linear PCM))24p

Like I said in the other thread, this looks like an issue with the hard drive not keeping up.

The right solution is to use a fast USB3 or Thunderbolt drive.

As a temporary measure, switching playback to "better performance" (this is done by clicking the little triangle at the top right of the viewer) will probably help.

As we are talking about it, while the "Fusion Drive" is a great idea, it is likely not providing any help here, so if you were thinking that the drive should be fast for video, think again.

The big video files are most likely in "hard drive part" of the fusion drive, and playback is not helped by the ssd. (In fact, this is as should be, otherwise these would be crowding out the multiple smaller files that need to be loaded time and again and whose placement in the ssd provides the most speed benefits).

You can use BlackMagic Disk Speed Test to measure the throughput of a drive, but there is more than that at play.

There are, as you found out, files that QT can play without trouble but FCP X struggles with. This has to do with the fact that one is doing a lot more than the other. It is very likely that BlackMagic DST will give a result that tops the 500Mbps for your system drive, but remember that the same drive is being solicited all the time, plus FCP X will need enough breathing room to render and display these large frames in real time, ie there data access time plus calculation  time plus display time, so that 30 frames per second appear immaculately on your screen, and audio is played to match.

So if the disk thoughput matches or barely exceeds the data rate of the file doesn't mean that it can be played without stutter.

That said, I agree that it is bit unusual that audio seems to suffer, but not video...

Here it is 7 months after this original post and the issue is still occurring. I recently had the same issue with video and audio files that I merged using PluralEyes 3. The source file that PE creates plays fine but when I playback these files in FCPX the audio drops out. It is very intermittent. I find that pausing the playback and hitting play will bring the audio back but it still has the drop out. I also used MPEGStreamclip to encode my H.264 Canon files to a ProRes4444.

I had exactly the same problem and I was able to diagnose it down to an Izotope RX4 plugin I was using on my Macbook Pro.

The weird thing is that if I render it on the iMac 27, it would do it fine with no dropouts, but it would only have dropouts on the MBP.  I'm still debugging but if I switch off the RX 4 Dialogue Denoiser, the gaps go away so now I'm just playing around with the settings (although I feel I shouldn't have to just to stop the dropouts from happening).

Yes I found that if the plugins were loaded but not opened then they stayed in demo mode hence the dropouts so by opening the plugins the demo message disappeared and they worked as expected. I use iLok authorization so I don't know if that has anything to do with it even though the ilok is inserted. Unfortunately that meant I had a dozen or more iZotope plugin windows covering the screen! I've flagged it with iZotope support so we'll see what they have to say for themselves.