How does MQA identify itself?

[goldenears]

This is a technical question.

How do MQA files identify themselves to the device? I guess it's in the last few bits of the audio data, but how does it technically work? I'm guessing it just runs everything through a decoder and just doesn't process frames that don't pass a checksum test?

 

[Werner]

A periodic sub-code hidden as pseudo-random noise in the lower bits (although IIRC MQA can hijack bits at a pretty high level, e.g. in order to survive a 16-bit channel).

Concerning this robustness: it has been shown that an MQA file can be altered substantially without the authentication failing.

 

[mansr]

A periodic sub-code hidden as pseudo-random noise in the lower bits (although IIRC MQA can hijack bits at a pretty high level, e.g. in order to survive a 16-bit channel).

This document describes it: https://code.videolan.org/mansr/mqa/blob/master/mqa.rst

Concerning this robustness: it has been shown that an MQA file can be altered substantially without the authentication failing.

The low 8 bits (sometimes more) can be stripped/altered, and the file will still be recognised by a decoder. This is how MQA-CD is made.

 

[goldenears]

Thanks for the answers everyone!