I recently purchased a pair of Sony MDR-1000X Bluetooth noise-cancelling headphones. Although I usually prefer Sennheiser headphones (my previous pair of NC headphones was the Sennheiser Momentum Wireless 2 (aka HD-1)), I went with the Sony due to their support of the AAC codec, as my primary devices are all Apple.
By default on OS X and MacOS, the headphones will connect with the SBC codec when playing audio. (And occasionally a fallback to the low-quality SCO streaming codec for some voice-chat apps like Cisco Jabber) The OS does support aptX and AAC over bluetooth, but you have to jump through some hoops to enable them. Why? who knows. My best guess is that it is becuase SBC is the universally supported (and required) codec for the A2DP Bluetooth audio profile, and using that maximizes compatibility and minimizes customer complaints. If you can’t reliably detect what a headset supports, then the lowest common denominator is the safe choice.
AirPods however do automatically use the AAC codec without the user having to set any options.
Update 4 Dec 2017:
Thanks to Anders Carling in the comments, looks like there is a much easier way to check and update these settings.
Open Terminal and enter “sudo defaults read bluetoothaudiod” and type in your password when prompted. You should then see the current settings:
"AAC Bitrate" = 128;
"AAC CBR" = 0;
"Apple Bitpool Max" = 64;
"Apple Bitpool Min" = 2;
"Apple Initial Bitpool" = 40;
"Disable HFP" = 0;
"Enable AAC codec" = 1;
"Enable AptX codec" = 0;
If you get an error “Domain bluetoothaudiod does not exist”, that means none of these settings have been set before, update the setting as shown below and you’ll be able to read the setting as outlined above.
To update these settings in the Terminal:
to enable AptX:
sudo defaults write bluetoothaudiod "Enable AptX codec" -bool true
to enable AAC:
sudo defaults write bluetoothaudiod "Enable AAC codec" -bool true
To disable either one, just change “-bool true” to “-bool false” at the end of the command.
Here’s the original method, still handy in case you want a GUI to toggle the settings:
To enable aptX or AAC support, you need to get a copy of Apple’s Bluetooth Explorer development utility.
Go to the Apple developer downloads page – you will need to register a developer account if you don’t already have one.
Search for “Additional Tools for Xcode” – at the time of this writing, the latest released version is for Xcode 9.0. This will download a .dmg file that contains “Bluetooth Explorer.app” – this is the only file you need, move it anywhere, and you can delete the rest.
If you’re already logged in to the developer site, you can also use this direct link for the 9.0 version:
For older versions you’ll get “Hardware IO Tools for Xcode 7.3”
Run Bluetooth Explorer, then go to Tools>Audio Options. Select “Enable AAC”. If you have an aptX-only device you can enable that here as well. If your headset is already connected, disconnect and reconnect. You don’t need to re-pair the device.
Once you’re reconnected, you can verify which codec you’re connecting with by enabling the Bluetooth menu bar icon (System Preferences >Bluetooth>Show Bluetooth in menu bar), then holding down option and clicking the Bluetooth menu bar icon and navigating to the headphones entry.
That’s it. You’ll be running the improved wireless codec, and should notice a definite improvement.
areilly.com 
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