NCS 2.6.0 has increased audio latency

[gocchan]

Hi, 

I have updated NCS to 2.6.0 and am evaluating nrf5340_audio, but when I measured the latency, it seems to have increased by about 15 ms compared to v2.5.0.

I attach the measurement results.

Is this value reasonable? Is there a way to make the latency similar to v2.5.0?

Regards,

Gotoda

nrf5340_audio_latency_comparison.xlsx

[Karl Ylvisaker]

Hello Gotoda,

Could you elaborate on your test setup in this case?
Could you also confirm exactly which configurations you are using in both cases?
Please provide the .conf files (located in the /build/zephyr/ directory) for both builds that was used in this measuring.

Best regards,
Karl

[gocchan]

Hello Karl, 

The same hardware (PCA10121) is used for v2.5.0 and v2.6.0 measurements. The measuring equipment and measurement conditions are also the same.
The measurement points are analog in and analog out.
Both were measured by implementing BIS firmware, but the results are similar for CIS.
Attach the respective .config files.

Best regards,
Gotoda

(v2.5.0).config(v2.6.0).config

[Amanda Hsieh]

Hi, 

Karl is out of the office for the Easter holiday, so I take this case. 

We do see the latency growing, the reasons are 

• PCFT and SDC treat max transport latency in a different way
  The default setting for BIS now is 20ms, and PCFT won't do anything further for this.
  But for SDC, the PTO (Pre-transmit Offset) mechanism will be triggered, so we can do pre-transmit for sending packets in different ISO intervals to make the transportation more reliable.
  However, the drawback is the growing of the latency
• To make the latency shorter (-10ms), please try to set CONFIG_BT_AUDIO_MAX_TRANSPORT_LATENCY_MS=10
  This can provide some help.

Please note that we are a bit low on staff due to the Easter holidays in Norway. So please expect some delays and thanks for your patience in advance.

Regards,
Amanda H.

[gocchan]

Hello Amanda,

What is PCFT?
By changing CONFIG_BT_AUDIO_MAX_TRANSPORT_LATENCY_MS from the default 20 to 10, the latency is now equivalent to v2.5.0.
Are there any disadvantages to changing CONFIG_BT_AUDIO_MAX_TRANSPORT_LATENCY_MS? Will sound quality be sacrificed?

Regards,
Gotoda

[Amanda Hsieh]

Hi Gotoda, 

gocchan said:

What is PCFT?

PCFT is the precompiled Bluetooth Low Energy Controller binary file for the LE Audio controller for nRF5340. See the release note:

The default controller has been changed from the LE Audio controller for nRF5340 to the SoftDevice Controller. See the nRF5340 Audio applications section in the Migration guide for nRF Connect SDK v2.6.0 for information about how this affects your application.

gocchan said:

Are there any disadvantages to changing CONFIG_BT_AUDIO_MAX_TRANSPORT_LATENCY_MS? Will sound quality be sacrificed?

The disadvantage is that the retransmission can only happen in a single ISO interval. Therefore, the packet drop could be significant in the noisy RF environment compared to the solution with PTO>0. 

Regards,
Amanda H.