Hi Nordic Team,
I’m currently using two standard nRF5340 DKs (non-Audio DK) running the nrf5340_audio application.
We’ve successfully adapted I²S speaker output on unicast, and we are now integrating a PDM microphone on the headset side.
Our setup is:
Gateway DK connected via USB to a laptop for audio I/O
Headset DK using a PDM microphone
Bidirectional mode enabled in Kconfig
Issue:
Speaker output works properly, but microphone audio is never sent back to the gateway/PC.
In reviewing the Kconfig, we noticed that enabling AUDIO_SOURCE_USB appears to force unidirectional operation and disables full-duplex (bidirectional) audio. Our suspicion is that this is preventing upstream audio from being sent over LE Audio.
Questions:
Is our understanding correct that AUDIO_SOURCE_USB currently only supports unidirectional audio and prevents microphone → gateway streaming?
If so, does this mean the nRF5340 Audio framework does not support full-duplex USB audio as the source/sink?
Potential Workarounds we are considering:
We want to verify whether any of the following would allow USB audio + PDM mic to function in bidirectional LE Audio mode:
Increasing audio buffer sizes to prevent USB-side starvation or overrun.
Running the system at 96 kHz instead of 48 kHz so USB Audio Class data paths remain valid while still doing LE Audio at 48 kHz internally.
Increasing allowable latency (e.g., frame queues, presentation delay) to ensure the system can process both TX and RX paths in time.
Since both DKs are fully code-modifiable, implementing our own dual-direction USB audio path if the Nordic default USB backend is currently unidirectional.
If these are not viable:
Would using a separate USB-to-I²S interface chip (so the nRF5340 only sees I²S for both playback and capture) be the recommended approach for achieving full-duplex USB to LE Audio bridging?
We want to confirm our analysis before redesigning our audio pipeline. Is there a simple fix to this?
Thank you for your assistance.
