Hey all. I've been messing around lately with my iPhone, and a laptop, and tablet, and various Bluetooth speakers, and BT transmitters and receivers, to connect to my Scarlett solo interface, and powered computer speakers, and headphones.

I don't necessarily have a specific question, rather how do a verify some sort of standard gain stage, or whatever.

For instance some of the BT headphones I have, have independent volume controls that change the volume/amp on the headphones themselves, while other ones, their volume control changes the volume on the iPhone itself.

So things have been a little confisong for me when it came to testing some mastering plugins on my tablet, where there was BT inlvolved. At that point small differences in gain can make a significant difference in the final product. Also it can make a difference in what I'm hearing and the associated adjustments.

Is there some sort of standard calibration process for gain staging and audio listening/playback system?

Thanks.