An AirPods Pro Firmware update may have actually made Active Noise Cancellation worse

An AirPods Pro firmware update released December 16 may have adversely affected Active Noise Cancellation, which led to the release being pulled a few days later.

According to the website RTINGS.com, Firmware update 2C54 for AirPods Pro, released December 16, brought with it a "fairly significant drop in isolation performance." According to their updated testing data:

Update 01/10/2020: After updating to Firmware 2C45, we retested the headphones and our results showed a fairly significant drop in isolation performance, primarily in the bass-range. This means that with ANC turned on, these headphones won't do nearly as good a job blocking out the low engine rumbles of planes or buses as they did before this update. This review reflects these changes.

The update did improve the bass accuracy of the AirPods Pro according to the site. They reported a "fairly significant improvement to bass accuracy" following the update. This seems to have been a tradeoff with very slight reductions in mid and treble accuracy. The changes to those, however, are so small you're likely not going to notice the difference.

The most confusing aspect of the story is that the 2C54 firmware update was actually pulled just a few days after its release, likely following the revelation that ANC was being significantly reduced by the change. This means that not all users will have downloaded the update, and so not everyone will be experiencing these issues. You can find out which firmware your headphones are running by heading to the 'About' section in your iOS General settings. Select 'AirPods Pro' and you'll be able to see which version you're on.

There is no indication at this stage as to whether Apple plans to re-release a fixed version of the firmware, or when it might do this.