aptX/aptX-HD/aptX-LL negotiates but produces no audio — FSC-BT1026D

HexPulse

I'm using FSC-BT1026D (sink, firmware V4.8.9, AT+PROFILE=1195) with a FSC-BT1035 source module.
With AT+A2DPCFG=0 (default), audio works correctly.
With AT+A2DPCFG=15 (AAC+aptX+aptX-LL+aptX-HD all enabled), the connection is stable but no audio comes out at all.
Note: the same sink unit plays audio correctly (with low latency) when paired with a different, third-party aptX-LL headset — so the issue seems specific to this source/config combination, not a total lack of aptX capability on the sink

FAE_Gavin

HexPulse Since the FSC-BT1026D can play audio normally with a third-party aptX-LL source, we'd like to collect more information to help identify the root cause.

Could you please provide the following?

The firmware version (AT+VER) of both the FSC-BT1026D and FSC-BT1035.
The complete configuration parameters of both modules (especially the outputs of commands such as AT+PROFILE, AT+A2DPCFG, and any other relevant settings).
The complete sequence of AT commands used during your test on both modules.

Once we have this information, we'll review the configuration and verify whether there are any compatibility or configuration issues. If necessary, we'll also reproduce the setup on our side for further investigation.

HexPulse

Unfortunately, I currently cannot establish a UART/AT connection to the source device (FSC-BT1035) to retrieve its configuration.

Here is the information for the sink side (FSC-BT1026D):

AT+VER: FSC-BT1026D,V4.8.9,20230420
AT+PROFILE: 1195
AT+A2DPCFG: 15

Complete AT command sequence used on the sink during bring-up:
AT
AT+VER
AT+BTEN=0
AT+PROFILE=1195
AT+A2DPCFG=15
AT+REBOOT
AT+BTEN=1
AT+NAME
AT+A2DPDEC

After the connection is actually established, querying AT+A2DPDEC returns:
+A2DPDEC=0

No audio is heard in this state.

FAE_Gavin

HexPulse Thank you for the information you've provided.

We noticed that the sink reports:

+A2DPDEC=0
However, this information alone is not sufficient for us to determine the root cause.

To investigate the issue, we need the complete UART logs from both modules (FSC-BT1035 and FSC-BT1026D) during the entire test process.

Please include:

All AT commands sent to both modules.
All responses and unsolicited events returned by both modules.
The complete process from power-up → configuration → Bluetooth pairing → A2DP connection establishment → audio playback attempt.

Since the codec negotiation involves both the source and the sink, we are unable to determine whether the issue is caused by the negotiation process or module configuration based on the sink-side information alone.

Once we receive the complete logs from both modules, we'll analyze them and reproduce the issue on our side if necessary.

HexPulse

FAE_Gavin
Hi, the device with which the connection was successfully established is the 1026D development kit; however, we are unable to play audio in LL mode using the 1026D on the board manufactured by our company.
Could it be a licensing issue?

Additionally, I noticed the following:
Development kit version: +VER=FSC-BT1026D,V4.8.7,20220322,
Our board: +VER=FSC-BT1026D,V4.8.9,20230420

FAE_Gavin

HexPulse
Regarding the firmware versions:

Development kit: FSC-BT1026D, V4.8.7, 20220322
Your board: FSC-BT1026D, V4.8.9, 20230420

The difference between V4.8.7 and V4.8.9 is relatively small, and V4.8.9 is actually the newer firmware version. Therefore, the firmware version itself is unlikely to be the main reason for the different behavior.

For the aptX-LL function on FSC-BT1026D, this feature requires an additional license authorization.

The development kit has completed the corresponding license authorization, so aptX-LL testing can work normally.

For your custom board/module, please provide the Bluetooth MAC address of the FSC-BT1026D module and contact your Feasycom sales representative to confirm whether the aptX-LL license was purchased and enabled when the module was shipped.

After confirming the license status, we can further check if any additional configuration is required.

You can also refer to the supported codec information here:
https://document.feasycom.com/docs/fsc-audio/EN/latest/bt1026x/3-functional-features.html