Apple - AirPods: Extremely poor mic quality on Mac

OP here – I'd just like to add to the answer below, that I've been in contact with Apple Support.

Explanation

Apple claims that the poor Mono 8kHz quality which affects recording and indeed simultaneously playback on Mac when the AirPod microphones are activated, is because the SCO codec then gets employed over the entire Mac audio system. This is supposedly "expected behaviour" when trying to use the AirPods and other Bluetooth headsets together with a computer, according to Apple.

The AAC codec is normally used when just listening to playback on the AirPods. It's just very unfortunate that SCO – low-quality as it may be – upon AirPod microphone activation is not only limited to doing recording, but also displaces AAC and audio playback.

Apple Support claims that Apple is looking at this issue, and that improvements might be coming in future firmware updates, but I did not interpret that as a promise to be honest. But for the time being, I'd say that the benefits of making calls and so forth with AirPods on Macs are quite limited.

Current best practice

Current best practice is to use the Internal Microphone for Recording, and the AirPods for playback when conducting calls. Input and Output devices can be selected in System Settings > Sound or by ⌥-clicking the Volume icon in the macOS Menu Bar, and selecting devices there.

See the screenshots below:

I found this on the Apple Discussion boards:

... they are aware of the issues and a temporary workaround is to switch the mic from the AirPods mic to the internal microphone.

On the discussion post you referenced, there was 217 other people reporting that they too had this issue.

Also from a May 6th Apple Tool Box article:

Many of our readers are letting us know that their AirPods are experiencing a lot of challenges while using them with macOS. In particular, when the mic is used, the AirPods’ audio is very low fidelity and sound quality. Some iFolks claim that they cannot even understand the other person when video-chatting with apps like FaceTime, Hangouts, and Skype. And your callers also report that your voice sounds muddy or that they barely hear you at all.

Is there a fix?

Other than the workaround to use your internal mic, no. My advice is to return the unit to Apple. There may be a fix in a future update to macOS or the AirPod firmware, but only Apple knows when they will issue an update. Given that Apple "silently" released the last update, don't expect too much fanfare with the next one.

Personally, I would have returned them and/or opened a support case with Apple as they are the best ones to solve this issue.

This is not an issue with your "bluetooth chip" as per the comments. This would be easy to diagnose - test you MBP with other BT headsets. If the problem goes away, it's the AirPods.

As the answer already states, it's because the AirPods change to the SCO codec. The bad news is, there is no way to permanently change this in macOS High Sierra¹ - there was a way to fix it in macOS Sierra, so if anyone reads this and hasn't yet updated, try this:

Use Apple's developer tool Bluetooth Explorer. Then you can use Audio Options (under Tools in the menu bar) to force them to use the alternative codec aptX.

• Official download, if you're a member of Apple Developer:
  https://developer.apple.com/download/more/ (search for Additional Tools)
  That's also where it states that it requires macOS Sierra.
• Inofficial download, plus description with screenshots:
  http://www.theghostbit.com/2015/03/force-mac-os-x-to-use-aptx-with-your.html

Full disclosure: Unfortunately I can't try it myself. (This is the first time I regret updating to the newest Apple OS...)

¹ the temporary workaround from the other answer works, obviously, you just have to do it every time.