BLE BIS channels > 2

[Sudhanand]

Hello,

   We are currently evaluating the nrf5340 using the "nrf5340 Audio" development board. Part of the evaluation is to verify if the device can handle 3 TX mono streams in BIS mode. We started with the "nrf5340_audio" application (v 2.2.0). As a first step for this we set the following parameters

BT_ISO_MAX_CHAN  = 3

CONFIG_BT_AUDIO_BROADCAST_SRC_STREAM_COUNT   = 3

This resulted in encountering the following build assert  failure from the "le_audio_bis_gateway.c" file.

BUILD_ASSERT(CONFIG_BT_AUDIO_BROADCAST_SRC_STREAM_COUNT <= 2,
         "A maximum of two audio streams are currently supported");

  I checked the forum posts for anything related to this and found one (devzone.nordicsemi.com/.../408505) where it is stated that the audio controller can support upto 4 BIS streams.

  If the system is capable of hanling 4 BIS streams, we would like to understand why the restriction to 2 streams is enforced in this application. Are there any system/hardware limitations to supporting more than 2 BIS streams or is this just specific to just the nrf5340_audio application?

Thanks you.

[JONATHAN LL]

Hi,


Features that is not listed here in our feature matrix is not guaranteed to work, so we only support two BIS. That does not necessarily mean that it will not work. 

So it is possible to increase the BIS to more then two but its at your own "risk" type of situation. 3 or 4 seems to be doable but I have not tested this. 



Adding links here including the one you referenced as relevant to topic:

https://devzone.nordicsemi.com/f/nordic-q-a/94823/nrf5340-audio---6-streams-broadcasting/401008 

https://devzone.nordicsemi.com/f/nordic-q-a/96061/nrf5340-audio-dk-multiple-bis-streams-from-a-single-dk 

https://devzone.nordicsemi.com/f/nordic-q-a/94690/is-there-any-resource-which-includes-two-or-more-musics-in-a-stream-for-bis-demo/399853 

https://devzone.nordicsemi.com/f/nordic-q-a/96061/nrf5340-audio-dk-multiple-bis-streams-from-a-single-dk 


Looking a bit more in to this and will update with anything I can find that helps.

Regards,
Jonathan

[JONATHAN LL]

Minor update:

BIS > 2 it might work but we cannot guarantee the stability. BIS = 2 or less is something we have tested and can guarantee will work. 

Also, encoding a 48kSpS 96kbps 16 bits audio stream needs ~33 % CPU usage, 3 BIS could consumes too many CPU resource.
Low down the bitrate might do some help, but that is something we don't recommend this.  So its up to you to do some trail and error to see what is expectable for your application.  

But do feel free to ask about anything and we will try to help as best we can, so if you get stuck somewhere then pleas continue with the inquiries 

Regards,
Jonathan

[Sudhanand]

Thank you for the clarification Jonathan. I will reach out if I have further questions.