LE Audio streaming between two dev boards is intermittently dropping

[mkimhj]

Hello,

I have configured 2 nRF5340 boards for LE audio streaming from my mac. Two things I am noticing:

1. The audio is streaming but it is intermittent. Audio plays for about 1-2 seconds before it drops for another 1-2 seconds and then this cycle repeats.

2. The logs indicate that the LC3 codec is configuring for 24000, but nowhere in my configuration is this happening (I am using the project defaults for the nrf5340 audio demo). 

HL [00:00:01.757,843] <inf> le_audio: LC3 codec config for sink:
HL [00:00:01.757,843] <inf> le_audio: Frequency: 24000 Hz
HL [00:00:01.757,843] <inf> le_audio: Duration: 10000 us
HL [00:00:01.757,843] <inf> le_audio: Channel allocation: 0x1
HL [00:00:01.757,843] <inf> le_audio: Octets per frame: 60 (48000 bps)
HL [00:00:01.757,873] <inf> le_audio: Frames per SDU: 1
HL [00:00:01.777,832] <inf> le_audio: LC3 codec config for source:
HL [00:00:01.777,832] <inf> le_audio: Frequency: 24000 Hz
HL [00:00:01.777,832] <inf> le_audio: Duration: 10000 us
HL [00:00:01.777,862] <inf> le_audio: Channel allocation: 0x1
HL [00:00:01.777,862] <inf> le_audio: Octets per frame: 60 (48000 bps)
HL [00:00:01.777,862] <inf> le_audio: Frames per SDU: 1

[Amanda Hsieh]

Hi, 

Are you using macOS? If so, it's a known issue: 

"OCT-2154: USB audio interface does not work correctly on macOS. The audio stream is intermittent on the headset side after connecting the gateway to a Mac computer and starting the audio stream."

Regards,
Amanda H.

[mkimhj]

Thanks Amanda. I'll switch over to using the 3.5mm jack for now.

Do you know what part of the project is responsible for configuring the LC3 codec to be at 24kHz instead of 48kHz?

[mkimhj]

Yes, but where in the actual source code is this default being set? I'd like to override this to 48kHz because the audio quality does not sound great.

[mkimhj]

Is it a matter of setting the choice in prj.conf like below?

CONFIG_BT_AUDIO_PREF_SAMPLE_RATE_48KHZ=y?

[Amanda Hsieh]

The default setting is from this line https://github.com/nrfconnect/sdk-nrf/blob/v2.9.0/applications/nrf5340_audio/src/bluetooth/Kconfig#L45 

[mkimhj]

Thanks Amanda,

Looks like setting CONFIG_BT_AUDIO_PREF_SAMPLE_RATE_48KHZ=y inside prj.conf does the sets the sampling rate I am looking for, but I think I am missing some other configuration. I am hearing an audio artifact that sounds like a birp chirping between two different frequencies. 

I feel like I am missing some higher level configuration which will properly set the sampling rate to 48kHz. Setting CONFIG_BT_AUDIO_PREF_SAMPLE_RATE_48KHZ=y in isolation seems like it is not working as intended. Are there other configurations that need to be changed? I would have expected the default for this project to sample at 48kHz but that does not seem to be the case.

[Amanda Hsieh]

What NCS version are you using? Are you using Broadcast sink and Broadcast source?

The default sampling rate is 48kHz. Could you try the unmodified nRF5340 Audio applications?

The log would look like this:

[mkimhj]

I am using 2.9, and I see 'unicast server' and 'unicast client' in the logs, so I do not think I am using the broadcast mode.

[Amanda Hsieh]

Got it. Try the unmodified nRF5340 Audio applications for the default sampling rate of 48kHz.

[mkimhj]

Hi Amanda,

I loaded the unmodified project and that seems to be streaming at 48kHz over LC3. This is interesting because the process I followed was copying this example project for the new one -- I'm not exactly sure what caused the sampling rate to change to 24kHz.

The unmodified audio application stops streaming after a few seconds which seems like a known issue.

The only change I've made to the unmodified application is

CONFIG_AUDIO_SOURCE_I2S=y

so that I can use the LINE_IN and pass in audio via an aux cable. This exhibits the same bird chirping behavior I mentioned earlier. I've attached a video for reference.

Are there any solutions for this problem? Has an external USB audio sound card been used to try and work around the mac USB issue?

[Amanda Hsieh]

Hi,

mkimhj said:

The only change I've made to the unmodified application is

CONFIG_AUDIO_SOURCE_I2S=y

so that I can use the LINE_IN and pass in audio via an aux cable. This exhibits the same bird chirping behavior I mentioned earlier.

Could you provide the device logs from both sides?

-Amanda H.

[mkimhj]

Hi Amanda, Below are the logs:

*** Booting nRF Connect SDK v2.9.0-7787b2649840 ***
*** Using Zephyr OS v3.7.99-1f8f3dc29142 ***
GW [00:00:00.268,249] <inf> board_version: Compatible board/HW version found: 1.1.0
GW [00:00:00.300,598] <inf> fw_info:
nRF5340 Audio nRF5340 Audio DK cpuapp
NCS base version: 2.9.0
Cmake run : Fri Jan 24 09:23:57 2025
GW [00:00:00.300,598] <inf> fw_info: ------- DEBUG BUILD -------
GW [00:00:00.300,628] <inf> fw_info: Compiled for GATEWAY device
GW [00:00:00.373,748] <inf> bt_mgmt_ctlr_cfg: Controller: SoftDevice: Version 6.0 (0x0e), Revision 8299
GW [00:00:00.373,931] <inf> bt_mgmt: Local identity addr: D2:5F:7A:D9:31:2B (random)
GW [00:00:00.405,059] <inf> bt_mgmt_scan: Local addr: 5C:E2:CC:C0:F8:3F (random). May time out. Updates not printed
GW [00:00:00.405,090] <inf> bt_mgmt_scan: Scanning successfully started
GW [00:00:00.409,362] <inf> bt_mgmt_scan: Creating connection to bonded device: D0:5B:8C:A4:B4:FE (random)
GW [00:00:00.414,398] <inf> bt_mgmt: Connected: D0:5B:8C:A4:B4:FE (random)
GW [00:00:00.414,428] <inf> main: Connection event. Num connections: 1
GW [00:00:00.484,771] <inf> main: Security changed
GW [00:00:00.695,007] <inf> bt_vol_ctlr: VCS discover finished
GW [00:00:01.045,043] <inf> main: Set members found: 1 of 2
GW [00:00:01.046,173] <inf> bt_mgmt_scan: Local addr: 5C:E2:CC:C0:F8:3F (random). May time out. Updates not printed
GW [00:00:01.046,173] <inf> bt_mgmt_scan: Scanning successfully started
GW [00:00:01.344,848] <inf> unicast_client: Discovered 1 sink endpoint(s) for device 0
GW [00:00:01.366,302] <inf> unicast_client: LEFT sink stream configured
GW [00:00:01.366,333] <inf> le_audio: LC3 codec config for sink:
GW [00:00:01.366,333] <inf> le_audio: Frequency: 48000 Hz
GW [00:00:01.366,333] <inf> le_audio: Duration: 10000 us
GW [00:00:01.366,333] <inf> le_audio: Channel allocation: 0x1
GW [00:00:01.366,363] <inf> le_audio: Octets per frame: 120 (96000 bps)
GW [00:00:01.366,363] <inf> le_audio: Frames per SDU: 1
GW [00:00:01.804,840] <inf> unicast_client: Stream 0x200122b0 started
GW [00:00:01.833,038] <inf> audio_datapath: Drft comp state: CALIB
GW [00:00:01.933,044] <inf> audio_datapath: Drft comp state: OFFSET
GW [00:00:02.233,001] <inf> audio_datapath: Drft comp state: LOCKED

_________________________________

*** Booting nRF Connect SDK v2.9.0-7787b2649840 ***
*** Using Zephyr OS v3.7.99-1f8f3dc29142 ***
HL [00:00:00.268,981] <inf> board_version: Compatible board/HW version found: 1.1.0
HL [00:00:00.301,605] <inf> fw_info:
nRF5340 Audio nRF5340 Audio DK cpuapp
NCS base version: 2.9.0
Cmake run : Fri Jan 24 09:19:34 2025
HL [00:00:00.301,605] <inf> fw_info: ------- DEBUG BUILD -------
HL [00:00:00.301,605] <inf> fw_info: HEADSET left device
HL [00:00:00.374,298] <inf> bt_mgmt_ctlr_cfg: Controller: SoftDevice: Version 6.0 (0x0e), Revision 8299
HL [00:00:00.374,511] <inf> bt_mgmt: Local identity addr: D0:5B:8C:A4:B4:FE (random)
HL [00:00:00.403,106] <wrn> unicast_server: CSIP using the default SIRK, must be changed before production
HL [00:00:00.407,623] <inf> bt_mgmt_adv: Local addr: 5E:FD:8C:4C:92:83 (random)
HL [00:00:00.407,714] <inf> bt_mgmt_adv: Adv directed to: D2:5F:7A:D9:31:2B (random).
HL [00:00:00.408,294] <inf> bt_mgmt_adv: Advertising successfully started
HL [00:00:00.438,903] <inf> bt_mgmt: Connected: D2:5F:7A:D9:31:2B (random)
HL [00:00:00.438,934] <inf> main: Connection event. Num connections: 1
HL [00:00:00.439,086] <inf> bt_mgmt_adv: RPA (Resolvable Private Address) expired.
HL [00:00:00.439,178] <inf> bt_mgmt_adv: Local addr: 5E:FD:8C:4C:92:83 (random)
HL [00:00:00.509,979] <inf> main: Security changed
HL [00:00:00.510,192] <wrn> bt_gatt: Device is not subscribed to characteristic
HL [00:00:00.510,192] <wrn> bt_pacs: PACS notify failed: -22
HL [00:00:00.989,837] <inf> bt_content_ctrl_media: Discovery of MCS finished
HL [00:00:01.380,737] <inf> le_audio: LC3 codec config for sink:
HL [00:00:01.380,737] <inf> le_audio: Frequency: 48000 Hz
HL [00:00:01.380,767] <inf> le_audio: Duration: 10000 us
HL [00:00:01.380,767] <inf> le_audio: Channel allocation: 0x1
HL [00:00:01.380,767] <inf> le_audio: Octets per frame: 120 (96000 bps)
HL [00:00:01.380,767] <inf> le_audio: Frames per SDU: 1
HL [00:00:01.400,634] <inf> main: Presentation delay 3000 us is set by initiator
HL [00:00:01.746,826] <inf> unicast_server: Stream 0x20010fec started
HL [00:00:01.759,429] <wrn> audio_datapath: Data received, total under-runs: 1
HL [00:00:01.867,431] <inf> audio_datapath: Drft comp state: CALIB
HL [00:00:01.967,437] <inf> audio_datapath: Drft comp state: INIT
HL [00:00:01.968,444] <inf> audio_datapath: Drft comp state: CALIB
HL [00:00:02.068,450] <inf> audio_datapath: Drft comp state: OFFSET
HL [00:00:02.468,597] <inf> audio_datapath: Drft comp state: LOCKED
HL [00:00:02.477,050] <inf> audio_datapath: Pres comp state: MEAS
HL [00:00:02.587,066] <inf> audio_datapath: Pres comp state: WAIT
HL [00:00:02.727,050] <inf> audio_datapath: Pres comp state: INIT
HL [00:00:02.737,060] <inf> audio_datapath: Pres comp state: MEAS
HL [00:00:02.847,045] <inf> audio_datapath: Pres comp state: LOCKED