7.How to switch Bluetooth codec for RETRO NANO in your Android mobile phone?

The RETRO NANO is a Bluetooth receiver. So the Bluetooth code it receives is depended by the mobile phone terminal. If you would like to switch the Bluetooth code, you could go to the developer mode page of the mobile phone for switching. 
There is a Bluetooth code selection option of RETRO NANO in the FiiO Control App. You could select the Bluetooth codecs you want to use on the RETRO NANO via that option. The codecs that are not selected will be disabled.

If you would like to use other Bluetooth codec（Like LDAC）, please follow this steps for help:
1. Enter FiiO Control App-RETRO NANO-Status
2. Click 'Select Bluetooth code'
3. Uncheck other Bluetooth protocols, leaving only the "LDAC" option, and click 'OK'
4. The RETRO NANO will restart and reconnect to the mobile phone via LDAC or other Bluetooth codec.

Note: The iOS device only supports SBC and AAC Bluetooth codec. And the default Bluetooth codec will be AAC.