General guidance for using the nRF5340 to transmit multiple audio signals over Bluetooth LE

RE: General guidance for using the nRF5340 to transmit multiple audio signals over Bluetooth LE

shamboozled — Tue, 06 Jun 2023 16:20:32 GMT

Hi Elfving,

Thanks for getting back to me. I will try to make these examples work. In the meantime, however, I am having some trouble getting the ADC to sample at the desired frequency of 8 kHz, but I will launch a separate ticket for that issue.

Thanks!

RE: General guidance for using the nRF5340 to transmit multiple audio signals over Bluetooth LE

Elfving — Thu, 01 Jun 2023 14:57:32 GMT

Hello again, and sorry about the delay

[quote user="shamboozled"]

From your feedback, my team has decided it is not necessary to receive the audio in real time. Instead, we would like to save the recordings in memory, and then upload the data after the recordings have completed.

[/quote]

That sounds good. So if you can live without live play-back and those features you would get from LE Audio, you can get a by with just using normal BLE for this. If you want to go for this, you could consider either using OTS (there is a small sample available in zephyr) or SMP. I would recommend starting by having a look at this SMP zephyr sample and how you can use it to send a file.

[quote user="shamboozled"]Would this be possible to do in real time?[/quote]

Well that could be an idea if all the signals where to stay put once chucked into the channel there, but the issue is the LC3. The LC3 isn't sending it in its raw form, the encoding and decoding would scramble everything.

Regards,

Elfving

RE: General guidance for using the nRF5340 to transmit multiple audio signals over Bluetooth LE

shamboozled — Fri, 26 May 2023 15:34:40 GMT

Hi Elfving,

Just to clarify, I do not need to hear the audio, just communicate the time series data over Bluetooth. Therefore, 4 channels at 8 kHz should be equivalent to 1 channel at 32 kHz. As long as the correct order is preserved, I think we only really need to communicate over one stream. Would this be possible to do in real time?

Thank you!

PS: I realize that I said 8-bit audio in an earlier post, but I meant 12.

RE: General guidance for using the nRF5340 to transmit multiple audio signals over Bluetooth LE

shamboozled — Fri, 26 May 2023 15:09:08 GMT

Hi Elfving,

Thank you for getting back to me.

Specifically, we would like to record for 10 seconds, sample at 8 kHz, and use 12-bit precision. With 4 channels, this should take up 480 kB. Does this seem like a more realistic goal? If so, how would you recommend we begin to implement this?

RE: General guidance for using the nRF5340 to transmit multiple audio signals over Bluetooth LE

Elfving — Fri, 26 May 2023 12:50:58 GMT

Hello again,

After looking further into this it seems that another current limitation is on the amount of streams: our LE Audio controller does not support 4 concurrent streams as of now. You can try to circumvent this by packing it into 2 stereo CIS streams however.

When it comes to CPU limitations this might work, but it might be on the edge of what the nRF5340 can handle.

Considering this, could you expand a bit on the real-time constraints of your product? Latency, range, and how detrimental would it be if the audio was a bit choppy?

Regards,

Elfving

RE: General guidance for using the nRF5340 to transmit multiple audio signals over Bluetooth LE

shamboozled — Wed, 24 May 2023 14:24:48 GMT

Hi Elfving,

Thank you for responding!

I am working on a device that records audio at 4 different locations for a medical application. To clarify, we are using a sampling rate of 8 kHz and a bit-depth of 8, so the raw bitrate should be 256kbps with 4 channels. Is it not possible to transmit at this rate?

RE: General guidance for using the nRF5340 to transmit multiple audio signals over Bluetooth LE

Elfving — Wed, 24 May 2023 13:57:27 GMT

Hello,

[quote user=""]I am currently trying to read and transmit 4 audio signals in real time over Bluetooth LE with the nRF5340 DK[/quote]

Okay, that sounds like a lot. Some tests on our LE Audio stack shows that we're using about 30% of our CPU on encoding 1 stream of 96 kbps, and 15% to decode. With two streams you do not have too much to go on for other tasks, but 4 sounds impossible on the nRF5340.

Could you expand a bit on your use case and why you need all 4 streams?

Regards,

Elfving