Airpods 3 using AAC-ELD on macOS?

Solution 1:

The ALT+Bluetooth menu was removed in MacOS Monterey, which is also the first version to support AirPods 3, so there is now way to check it anymore. Even their Bluetooth Explorer Developer Tool either does not work anymore or does not tell you that specific detail.

However, the Console app (not the Terminal) does log what codec is negotiated. And there you see, even my AirPods Pro's now use AAC-ELD at 24000 Hz.

The sample rate of 24000 Hz is still not what I would call "HD", but better than the 16000 Hz of the previous mSBC profile. If you want to know more, then I recommend ValdikSS excellent article about bluetooth audio.

Solution 2:

Nemo64 I just wanted to add a bit of context to your answer, but I'm am not allowed to comment yet.

The sample rate of 24000 Hz is still not what I would call "HD"

AAC-ELD uses Spectral Band Replication (SBR) similar to HE-AAC. HE-AAC encodes one main audio stream and a secondary SBR stream. The main stream is encoded using plain AAC at a reduced sample rate. Typically half. An additional SBR stream encodes the remaining bandwidth by differencing with the main audio stream (à la MP3's Joint Stereo). When you see a HE-AAC or AAC-ELD stream reporting 24000Hz, the codec is reporting the sample rate of the base stream. SBR is a second decode pass that is able to "unfold" the higher frequency portion of the audio. This is also backwards-compatible, since a normal AAC decoder will only "see" the main stream and play it at half bandwidth. A compliant HE-AAC or AAC-ELD decoder will be able to decode the full bandwidth.

tl;dr AAC-ELD reports half of the bandwidth encoded. 24000hz here actually means 48000Hz.