Quote:
Originally Posted by Viffermike
That's because your iPhone 6, or any other device that is using Bluetooth ( mecodoug ) , is actually sending digital instructions to increase or decrease volume at the terminus end of the half-duplex Bluetooth signal -- IOW, your HU. That volume could be input gain, pre-amp gain, power-amp gain, or master volume -- all that is determined by the audio processor, NOT the source device, when Bluetooth is in use. Basically, Bluetooth is transmitting the same kind of digital instruction as it does when you skip a song or answer a call.
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Obviously BMW has implemented AVRCP control functions that allows the iPhone stored volume level from 0x0 to 0xF in the A2DP profile for the Bluetooth connection to the BMW HU, to be interpreted - from a functionality perspective the same effect a 16 position analog volume pot would have on an analog connection into an AUX input.