Bad quality of Audio stream on RF5340 Audio application - NCS v2.8.0

RE: Bad quality of Audio stream on RF5340 Audio application - NCS v2.8.0

Maria Gilje — Tue, 14 Jan 2025 14:36:24 GMT

Hello Omri,

First I want to apologize for the wait you have had.

[quote user="Omri"]The audio quality is acceptable only when the ACL connection interval is a multiple of 10ms.[/quote]

This is expected as the connection interval is required to be a multiple of the ISO interval. See for example the description for CONFIG_BLE_ACL_CONN_INTERVAL.

[quote user="Omri"]

This is why updating the connection interval to 90ms did not impact the audio streaming quality.

Could this be a limitation of NCS v2.8.0?

[/quote]

The requirement is also for nRF Connect SDK v2.9.0. That being said, we do recommend starting out projects on the latest tagged release of nRF Connect SDK.

[quote user="MahendraTailor"]Be aware that with LC3 the standard PLC (Packet Loss Concealment) is not good at masking lost pure tone packets.
In fact, use a pure tone (432Hz) to hear packet loss as every single loss can be heard as an audio artifact.[/quote]

This is a good and correct comment from MahendraTailor. I also want to add that the reason for this is that LC3 is designed for music and speech and subjective measurements (perceived quality).

Again, my apologies for the late reply.

Best regards,

Maria

RE: Bad quality of Audio stream on RF5340 Audio application - NCS v2.8.0

Omri — Thu, 12 Dec 2024 09:58:44 GMT

Hi,

I would like to correct my earlier response.

The audio quality is acceptable only when the ACL connection interval is a multiple of 10ms.

This is why updating the connection interval to 90ms did not impact the audio streaming quality.

Could this be a limitation of NCS v2.8.0?

RE: Bad quality of Audio stream on RF5340 Audio application - NCS v2.8.0

Omri — Tue, 10 Dec 2024 14:45:06 GMT

I was referring to the ACL connection interval, which is set to 8 (10 ms) by default in the nRF5340 Audio application.

This interval is used from the moment the ACL connection is established until the audio streaming is configured.

Once the streaming is configured and started, the application updates the connection interval to 72 (90 ms).

I noticed that the audio quality is solely dependent on the ACL connection interval at the time the connection is established.

It does not seem to be affected by whether the application performs a connection update later or not.

RE: Bad quality of Audio stream on RF5340 Audio application - NCS v2.8.0

MahendraTailor — Tue, 10 Dec 2024 11:50:37 GMT

Hi Omri

Be aware that with LC3 the standard PLC (Packet Loss Concealment) is not good at masking lost pure tone packets.
In fact, use a pure tone (432Hz) to hear packet loss as every single loss can be heard as an audio artifact.

As to why audio degrades when <sic: ACL> connection interval is changed beats me and look forward to how Nordic respond.
Did you mean by any chance the ISO interval - which should be left at 10ms or multiples of it when BN>1?
In fact during a unicast audio, why the need for a 10ms connection interval? A phone is unlikely to even allow you that as even MIDI is only allowed 11.25ms on an iPhone.