Does the MQA light guarantee a perfect file rip?

(Chris ) #1

It’s interesting, that if you rip an MQA file and the MQA light comes on, it must be perfect.

Was Anyone Hoping that CD Ripping Would Be the Next Feature Enhancement?
(Andrew Cox) #2

Depends how the authentication is implemented. If there is a check sum for the file in the process, then yes. If it just sets a bit or uses some other ID mechanism then not necessarily.

Those who know for sure what is under the hood are constrained by an NDA or licence and may regard it as imprudent to say anything given the febrile nature of MQA discussions.

If the authentication light turns on when streaming, before the whole file has been downloaded, then I would guess that a checksum is not involved.

(Martin Webster) #3

I’m sure I read somewhere that crippled MQA files have been shown to authenticate, i.e. blue light displays.

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(Chris ) #4

The whole point of MQA is that it is authenticated and if the file is corrupted it will not authenticate. That’s it.
If there are some false positive issues out there, I’m sure they will be technicalities that will be ironed out.

(58LesPaul) #5

@Martin_Webster - Yes, I remembered seeing this at the Audiophile Style site a while back; I went back and found it:

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

I especially like this part:

When FredericV poses the question:

“So if the real MQA file, and stripped version with only 16 bits of entropy, both show decoding to 24/352.8, how does the customer know he is not being scammed?”

And user mansr says:

“Easy, if the blue light is on, it’s a scam”

:joy:

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(Andrew Cox) #6

Thankyou @58LesPaul, a most interesting thread. Mansr described the authentication process as follows, not sure how he knows:

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.

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#7

The word is bit perfect. As long the ripping is lossless, any authenticated information is left intact. It doesn’t matter whether the first 16 bit carries the authenticated information; any data change will affect the entire file and render it undecoded.

#8

After all, MQA is actually a 16 bit (17 bit after dithered) which is transported on a 24 bit data file. It came with no surprise at all. The ‘scam’ you are seeing is simply referring to the ‘24 bit data’.

As with authentication done in the first 16 bit, that’s where all the audible music details are captured. The upper 8 bit is a lossy compression for capturing some high frequency components; my take is it useless to authenticate something that is already lossy in nature. To me I agreed the whole thing looks like a partial ‘scam’ when it comes to the blue light.

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(Chris ) #9

No musical information is lost in MQA

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#10

You have to rely on words of mouth (MQA) rather some kind proof of testing, which is unfortunate.

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#11

I’d wager that opening any MQA encoded audio file in a hex editor, making random changes to the audio stream and saving them will still see the little blue light illuminate. Make the changes toward the latter half of the file so there’s no chance of damaging your speakers when the DAC tries to convert the changes to analog signal (i.e. you don’t want to play that part of the stream). I’d be very surprised if MQA is not indicated by a byte sequence added somewhere in the audio stream (presumably at/near the beginning) where the original audio content has been discarded in order to store the so-called magic sauce used in the 2nd unfold to make the lossy replacement “better” than the original it corrupted.

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#12

Define ‘musical’.

(Julius Moshinsky) #13

You rely on what you hear. No one knows what a recording actually sounds like. Even if you are listening to a master tape on the analogue reel tape deck it was recorded (on), everything following changes it. If I could hear the Reiner Sheherazade sound like the best Lp reproduction I ever heard of it, but on MQA digital, without the Lp groove rumble and end of side tracing distortion, the solo violin hovering in the air like it only does it a really great seat in a really great hall, I would be ecstatic over the MQA reproduction, no matter how many bits involved or what manipulations have been employed. Mammalian psychoacoustics is far more complicated than physics-level reductionists would like to believe.

(Peter Lie) #14

16-bit truncation is a feature to survive 16-bit transmission such as AirPlay.

MQA light at a certain instant does not guarantee perfect ripping for the whole file. If the MQA authentication remains on for the whole file (MQA CD rip) then it may be an evidence of perfect rip, but that is impractical to use as momentary loss of the light can potentially be missed by simple visual inspection.

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(JohnV) #15

And…WE’RE OFF!!

MQA TAKE 37. QUIET ON THE SET… …ACTION!

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(Chris ) #16

Analog sound that can be perceived by Humans.

(Henry) #17

The MQA indicator doesn’t indicate a perfect rip, it indicates that the file contains readable MQA headers and information. And as MQA CD’s exist then it will not see anything at all wrong if presented with a 16 bit MQA encoded file so long as the headers are intact. And it shouldn’t be expected to either. MQA tell us they are correcting for the recording/mastering ADC and the 2nd unfold is DAC specific. Which as far as I can tell is irrelevant to the bit rate of the encoded file.

#18

I only have one MQA album, Fairytales by Radka Toneff. I bought it for the restoration work which is claimed to have taken place, not the MQA encoding. I could only obtain the 16/44.1 MQA version (from Tidal) and was a bit disappointed by this as the transfer for mastering was done at 24/192 (even if the original resolution was 16bit/50.35kHz). Also, John Atkinson of Stereophile reviewed a 24/48 MQA version. Is my copy inferior?

When I now learn that MQA most likely delivers everything as 16bit (or 15 bits + 1 for “origami”) and just adds 8bits of “nothing” to make it look good I can see the whole scam.

Fairytales sounds fine, probably more due to the restoration work than MQA.

(Chris ) #19

If it wasn’t for MQA, the restoration would never have been done.

#20

You are right about that, but proper MQA was supposed to be 24bit according to Bob Stuart. When 8bits below 16 is empty and can be discarded without change in the decoded output it is a problem I think…
Restoration of Fairytales is a special case, but what about all the other ‘normal 24bit’ MQA productions?