By supporting AAC Bluetooth, AAC files will be transmitted with less processing
A lot of laymen think so but it is not true.
It must be PCM otherwise you can’t do any kind of DSP like volume control, EQ, mixing (incoming phone call).
Finally the audio is send to the audio device, in this case the Bluetooth sender.
There the audio in encoded with the codec negotiated between sender and sink. The sink decodes it to back to PCM and send it to the DAC of the Bluetooth device.
Robert Trigss did an elegant experiment.
He took a AAC file, so one with a known frequency response and played it on a couple of phones including a iPhone.
As the frequency response differs from the original, obvious the AAC file has been decoded and encoded by the Bluetooth device using AAC as the transmission protocol.
Along with default SBC and Qualcomm's aptX, AAC is a commonly supported Bluetooth codec in the wireless headphone and speaker markets.
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