Hello,
Activate Developer options :
https://www.howtogeek.com/129728/how-to-access-the-developer-options-menu-and-enable-usb-debugging-on-android-4.2/
Enable Bluetooth HCI snoop log, connect your Bluetooth receiver and play a few seconds of music. Disable Bluetooth HCI snoop log.
Copy the log file (/sdcard/btsnoop_hci.log on your Android device) to your computer, install Wireshark, load the log file and filter packets with btavdtp.
You'll possibly see lines like theses :
Rcvd ResponseAccept - GetCapabilities - Audio SBC (16000 32000 44100 48000 | Mono DualChannel Stereo JointStereo | block: 4 8 12 16 | subbands: 4 8 | allocation: SNR Loudness | bitpool: 2..53)
Rcvd ResponseAccept - GetCapabilities - Audio non-A2DP (APT-X - 44100 48000, Stereo)
Rcvd ResponseAccept - GetCapabilities - Audio MPEG-2,4 AAC
(This happens when I connect a phone to a Sony MDR-ZX750BN)
Below these lines, I have :
Sent Command - SetConfiguration - ACP SEID [1 - Audio Sink] - INT SEID [1 - Audio Sink] - Audio SBC (44100 | JointStereo | block: 16 | subbands: 8 | allocation: Loudness | bitpool: 2..53)
because unfortunately my Nextbit Robin doesn't support aptX.
When I was connecting a Motorola moto E 2015 to the same cans, I got :
Sent Command - SetConfiguration - ACP SEID [3 - Audio Sink] - INT SEID [2 - Audio Sink] - Audio non-A2DP (APT-X - 44100, Stereo)
Hope it helps,
AiZ