Audio quality problem after 10.13.6 upgrade on 2010 Mac Pro

Soba

macrumors 6502
Original poster
May 28, 2003
272
293
Rochester, NY
I'm having a bizarre problem on my 2010 Mac Pro after upgrading from 10.13.5 to 10.13.6.

I usually use a Logitech USB headset for sound output. After upgrading to 10.13.6, audio quality was significantly worse through the headset. I would describe it is as muffled telephone quality, as if playing back a low-fidelity sound of 11KHz versus high-fidelity at 44KHz+. The problem occurred when playing audio in iTunes, web browsers, system sound effects, and other sources, so it seems all system audio is affected.

Now the bizarre part: the problem only occurs when the headset is plugged into the lower USB port on the front of my Mac Pro. Plugging it into the upper USB port, keyboard USB port, and a couple of others that I tried returns audio quality to normal.

Other output devices don't have this problem. I tried playing audio through analog headphones (apple earbuds) plugged into the headphone port, through the internal speaker, as well as through my HDMI display's built-in speaker and all have proper audio quality.

My workaround is just to use another port, which is fine by me, but any ideas why this is happening or for a permanent fix? I'm wondering if performance of that port will be affected for other devices, as well. I'm thinking of re-installing the update and perhaps filing a bug report.
 

Soba

macrumors 6502
Original poster
May 28, 2003
272
293
Rochester, NY
An update and solution for this, as I finally figured out what was happening!

The problem was not confined to just one port on the Mac Pro; it was a cascading effect from one USB port to another and it appeared whenever I restarted the Mac.

If I left the headset plugged into the top USB port on the front of the Mac Pro and rebooted, the quality would be poor after reboot. Moving to a different port would restore the audio quality to normal, but if I rebooted the Mac while connected to the new port, the quality would become poor on the new port, as well. And so on, for whichever port I tried. Any port where the problem appeared would provide poor audio quality indefinitely, even months later. This behavior appeared with all ports—even the ones on the side of the Apple keyboard.

Solution: I launched Audio MIDI Setup.app from the Utilities folder and found that the output quality for the headset was set at 8,000 Hz. I have not launched this app in years, so it looks like macOS was autonomously resetting the audio quality of my headset to its lowest level at boot time. This problem seems to have been introduced in 10.13.6.

Manually changing the quality back to 48,000 Hz using Audio MIDI Setup solved the problem. Very glad to have crisp audio again!
 

flowrider

macrumors 603
Nov 23, 2012
6,133
2,326
Glad you figured it out! Thanks for sharing. I use the aux port on my cMP into two powered Klipsch R-15PM speakers and a Klipsch R-10SW woofer. Luv the setup.

Lou
 

Soba

macrumors 6502
Original poster
May 28, 2003
272
293
Rochester, NY
I'm afraid that nice speakers would annoy my neighbors, but I hope to be out of my apartment and into a house next year, which will let me get rid of the headphones! :)
 
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