Active Noise Cancellation, an outward-facing microphone detects external sounds, which your AirPods Pro then counters with anti-noise, canceling the external sounds before you hear them. An inward-facing microphone listens inside your ear for unwanted internal sounds, which your AirPods Pro counter with anti-noise.
Transparency mode lets outside sound in, so you can hear what's going on around you. It’s a good idea to adjust the AirPods Pro’s Transparency mode to your liking.
Customize Transparency mode settings:
Check that you have the latest version of iOS or iPadOS.
Go to Settings > Accessibility > Audio/Visual > Headphone Accommodations > Transparency Mode.
Tap Custom Transparency Mode and turn it on. This will open up several options for you to tweak.
Amplification. If you move the slider left, you decrease amplification of background sounds while wearing your earbuds, and if you move it to the right, you increase it.
Transparency. Use this so that one ear lets in more or less outside noise. This is especially good for those who have hearing loss in one ear.
Tone. Move the slider left and Transparency mode will increase its focus on lower frequencies. Moving it right will make it focus on sounds with higher frequencies.