I am prototyping an iOS accessibility audio application for people with unilateral hearing loss.
The goal is simple.
Capture environmental audio using the AirPod on the poor hearing side and route that audio with very low latency into the AirPod on the working hearing side.
The core concept is already working on physical AirPods and an iPhone.
Our desired signal path is
Right AirPod microphone → iPhone audio processing → Left AirPod output
The user sets the AirPods microphone in Settings to Always Right AirPod. The app then captures that Bluetooth microphone and routes the signal into the left output channel.
Using AVAudioSession and AVAudioEngine we have successfully achieved low latency cross ear audio.
The main issue is native AirPods Transparency.
When the app activates the AirPods Bluetooth microphone using HFP, the transferred audio continues working correctly, but native Transparency audio on the receiving AirPod effectively disappears.
Interestingly, iOS still reports Transparency as enabled in Control Center and AirPods settings.
This means the user can hear audio transferred from the poor hearing side, but their working ear loses much of the normal environmental sound that Transparency previously provided.
We have tested several configurations.
- Normal Bluetooth HFP with playAndRecord
This provides the best result so far.
The AirPods microphone signal is strong.
The output route exposes two channels.
We can route the microphone signal only to the opposite AirPod.
Latency can be reduced enough that conversation feels nearly real time.
However, native Transparency on the receiving AirPod effectively stops providing environmental audio.
- bluetoothHighQualityRecording
Microphone quality is noticeably better.
However, latency is significantly higher and produces an audible delayed or echo effect during conversation.
Transparency has the same general issue.
- multiRoute with dualRoute
This allows the iPhone audio hardware and AirPods to operate simultaneously.
It appears to preserve more ambient awareness on the working side.
However, the AirPods microphone becomes substantially weaker when used as the secondary Bluetooth HFP input.
We measured the incoming AirPods microphone signal at roughly minus 40 dB during normal speech testing.
Adding 12 to 18 dB of software gain increases distortion without materially improving intelligibility.
- farFieldInput with dualRoute
We tested the raw AirPods microphone with and without farFieldInput.
The microphone levels and practical pickup were very similar.
Far field speech processing improved intelligibility somewhat, but did not solve the weak secondary Bluetooth input signal.
Our main technical question is
Is there a supported AVAudioSession configuration, Core Audio API, AirPods API, or entitlement that allows a third party application to capture an AirPods microphone while preserving the AirPods native Transparency processing on the output AirPod?
Ideally we want
Right AirPod microphone capture
plus
native Transparency on the left AirPod
plus
application generated right to left audio mixed into the left AirPod
all operating simultaneously.
We do not need access to Apple's Transparency microphone signal itself if native Transparency can simply remain active while our application audio is mixed into the receiving AirPod.
If this is not currently possible using public APIs, is this an intentional platform limitation of the AirPods Bluetooth microphone route?
We would also appreciate guidance on whether there is another recommended architecture for this accessibility use case.
The low latency cross ear routing itself works surprisingly well. Preserving natural environmental audio in the user's working ear while the Bluetooth microphone is active is currently the main technical blocker.
Testing has been performed on a physical iPhone running iOS 26.x using Xcode 26.6 and current AirPods hardware, not the Simulator.
Thank you for any guidance.