Why does the sound in my apple cinema display stop working?

Ongoing, intermittent issue: (specs at bottom of comment)

I primarily have my sound coming through the 27 inch display. For the most part, it works fine. As I'm watching something on youtube (or hulu, or other), the sound will break once or twice for a second... . about 30 sec – 1 min later, the sound will stop. The video is still playing.

My current remedy (and possible marker toward the issue) is to unplug the 27" USB connection for about 10-30 sec. During that time the sound will often revert to the 24" monitor. Occasionally, the sound will be out of sync from the video.

When I plug the 27" USB back into the laptop, the sound returns & usually stays.

See system specs below

MacBook Pro (Retina, 13-inch, Early 2015)

3.1 GHz Intel Core i7

16 GB 1867 MHz DDR3

Intel Iris Graphics 6100 1536 MB

2 (non thunderbolt) Apple Cinema Displays connected through 2 thunderbolt ports

also have them connected via USB.

Display 1: 27" Apple Cinema Display

Display 2: 24" Apple Cinema Display

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Chosen Solution

First your displays speakers (f you have the newer Cinema display) are feed from the displayPort connection via the Thunderbolt port off your system. So when you have a USB connection in addition to the displayPort's you've confused your computer which path to send the sound through!

So what happens here is your sound is taking a different route to the speakers which is slower! Which is why the sync is off between the mouth movement and the voice.

You should only have the displayPort connection of the display which has speakers. If you are using external speakers then you'll want to then use the USB port off of the display not the system to drive them. Make sure you've directed the sound output correctly by checking your Pref settings. If your second Cinema display also has speakers make sure they are disabled.

The last issue with out of sync sound can be the codec being used, make sure you have the latest version. In some cases your system may have resource issues. Make sure you have at least 1/4 of free space on your boot drive (internal SSD drive). I would also monitor your systems RAM usage. I like this app: Memory Clean.

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