Limits on BLE Audio ISO Broadcast Streams nRF5340 Audio DK

RE: Limits on BLE Audio ISO Broadcast Streams nRF5340 Audio DK

Hieu — Mon, 14 Apr 2025 12:15:05 GMT

Hi Simon,

It's good to hear things are working. I will close this case then, but please feel free to reopen it if you have a question on the same topic.

Regards,

Hieu

RE: Limits on BLE Audio ISO Broadcast Streams nRF5340 Audio DK

Simon32 — Fri, 11 Apr 2025 08:32:19 GMT

Hello Hieu,

Thanks a lot for your reply.

My main requirement is to support multiple audio channels for different languages in a conference setting, using Auracast. The goal is to broadcast several simultaneous streams that participants can select from individually.

At this stage, I'm focusing purely on evaluating how many BIS/BIGs I can handle on the nRF5340 Audio DK using pre-encoded LC3 files from an SD card. Real-time encoding isn’t a priority yet. But I expect this will become relevant later, so I might come back with questions at that point.

Thanks again for pointing out the airtime constraints and the relevant configuration options. I applied those changes and already managed to increase the number of streams beyond what I initially had. I’ll keep experimenting with airtime, bitrate, and retransmit settings to see how far I can push it.

Appreciate the guidance!

Regards,

Simon

RE: Limits on BLE Audio ISO Broadcast Streams nRF5340 Audio DK

Hieu — Mon, 07 Apr 2025 19:43:02 GMT

Hello Simon32,

Could you please share what kind of requirements you are having?

[quote user=""]1. Are the BIG and BIS limitations in the SoftDevice Controller defined by hardware/resource constraints, or are they configurable within the stack?[/quote]

There is a hard limitation with airtime. Thus, it should be technically possible to add more streams if you reconfigure the streams to use less airtime, such as lowering bitrate, number of retransmits.

[quote user=""]2. Are there specific SoftDevice or Zephyr stack configurations that could help extend these limits?[/quote]

There are two relevant configurations, CONFIG_BT_ISO_MAX_BIG and CONFIG_BT_ISO_MAX_CHAN.

[quote user=""]3. Has there been any update to the controller since the 6-streams discussion that could allow for more streams?[/quote]

This conversation is most likely outdated. It was 2 years ago, when SoftDevice Controller doesn't support LE Audio yet. As you know, now it is the default controller for LE Audio in NCS.

[quote user=""]When increasing the BIG count, I encounter a BUS FAULT and when increasing the BIS per BIG, I get an MPU FAULT. I understand that the nrf_auraconfig sample is designed for a maximum of two BIGs with four BIS streams each, but I am investigating whether these limits are soft constraints or hardcoded architectural limitations.[/quote]

I suspect this is stack usage issue. Please try to increase them. Refer to https://github.com/nrfconnect/sdk-nrf/blob/v2.9.1/samples/bluetooth/nrf_auraconfig/prj.conf#L17-L19.

Hieu