Truncating MQA files to 16 bits and the blue light still shines

[miguelito]

35 minutes ago, mansr said:

This is by design. The MQA identification and authentication data is embedded in bit 8 of a 24-bit PCM stream. Dropping bits 0-7 thus leaves it untouched. The authentication works by computing a Blake2s hash over the top 15 bits (the plain PCM portion) and parts of the control stream in bit 8. This hash is then verified against a cryptographic signature extracted from the control stream. The public key is stored in the decoder. If the signature matches, the blue light goes on. The low 8 bits encoding the high-frequency content are not covered by the authentication.

But if I understand the original poster correctly, it not only authenticates but somehow is upsampling to 352KHz... How does that work? What is the quality of the signal coming out? Would love to see it. Would also love to see the first unfold of this.

[miguelito]

On 2/22/2018 at 10:45 AM, mansr said:

Easy, if the blue light is on, it's a scam.

Delicious... 

 

It is truly embarrasing that a 16 bit file will trigger the “blue dot of cash” (cash for MQA Co). This effectively means that an “MQA validated” file can contain less than 16 bits of true musical data (since some is committed to lighting the fecking blue barf signal). What a fecking scam.

 

For the record: I have listened to a LOT of MQA from TIDAL. I have a fully decoding MQA DAC (see signature) and I can tell you this is a mixed bag at best.

[miguelito]

On 2/24/2018 at 10:12 AM, miguelito said:

It is truly embarrasing that a 16 bit file will trigger the “blue dot of cash” (cash for MQA Co).

It would be quite interesting to compare an MQA CD rip with the equivalent non-MQA rip. I bet you the diff is eq.

[miguelito]

There is an MQA version of this album on TIDAL rendering at 24/96. File prob exists for purchase somewhere. Like I said before, I suspect this is nothing more than EQ effectively.

[miguelito]

1 hour ago, GUTB said:

There seems to be no reason why it couldn't do checks against those bits, so I assume the omission is on purpose. Why? Well, the last 8 bits contain the ultrasonic unfold data, so I assume this was a choice MQA developers made in order not to break DAC hardware that can't accept more than 16 bit input. 

What do you mean "checks against those bits"? The only way to encode a signature is to use some of the data bandwidth.