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

[FredericV]

53 minutes ago, FredericV said:

Also note that flac can't compress the output of the decoder back to the MQA flac distribution file sizes. This suggest garbage is added which does not compress well (garbage because of aliasing and higher noise floor).

The fact that the flac encode of the MQA decoder output is almost twice the size of the distribution is logical: MQA uses leaky filters which mirror the baseband into the ultrasonics. So flac has to encode the same signal twice, once at normal amplitude, and it's attenuated copy (alias), which explains the almost double file size.

[mansr]

11 hours ago, FredericV said:

Also note that flac can't compress the output of the decoder back to the MQA flac distribution file sizes.

Hardly surprising. A decoded mp3 file compressed with FLAC is also larger than the original mp3.

[mansr]

10 hours ago, Don Hills said:

I am surprised that the MQA decoder doesn't seem to complain when it is fed the invalid compressed data.

If the expected markers aren't there, it is simply ignored. It has to work this way. If some software (player/OS) has mangled the lowest bits for whatever reason, the DAC still must play something.

[FredericV]

2 minutes ago, mansr said:

If the expected markers aren't there, it is simply ignored. It has to work this way. If some software (player/OS) has mangled the lowest bits for whatever reason, the DAC still must play something.

 

In Bob's official explication, truncating to 16 bits is supported. Some excuse about automotive and bluetooth which can truncate bit depth. But I can't find the page where this was posted. All I remember is the fact that it was once stated, so this was the reason for testing it.

[Don Hills]

Thanks, Frederic, Mans. It makes sense.

[FredericV]

Let's compare fake content from SOX's leaky upsample filter settings (lower waveforms, this is certainly not a standard sox filter that normal users would use) with MQA's leaky filter (upper waveforms), when in both cases the 1e unfold data is not available:

SOX has no access to MQA's secret internals in the 8LSB bits of the distribution file, so this is just noise.
MQA's decoder has no access to 8LSB bits of the distribution file when we blank those bits, or replace them with random noise, or with a repeated string such as "MQASHILL".

The SOX filter only attenuates with 1 dB, but it looks like MQA boosts the volume a little more. See my signature how this filter works.

As you can see, we can create fake +20 Khz spectrum with SOX, starting from the MQA distribution file:

Just like with MQA's leaky filters:

 

Looking at the normal 16 bit 44.1 file, this is the "normal" spectrum of a 44.1K file, which stops at 20 Khz:

 

Conclusion:

- leaky filters can be implemented in open source, and also create the fake content just like MQA
- the extra ultrasonic spectrum that a 50% larger MQA encoded wave file is offering (24 bit MQA wave file, vs truncated 16 bit MQA wave file), is minimal

So except for a licensing scheme, what purpose does the 1e unfold offer? Most of it's audible effects due to leaky filters can also be accomplished with OSS.
 

[mansr]

8 minutes ago, FredericV said:

So except for a licensing scheme, what purpose does the 1e unfold offer?

It undoes some of the dither applied to the PCM part as you can see in this plot of a silent bit in the file. DXD original included for reference.

[FredericV]

7 minutes ago, mansr said:

It undoes some of the dither applied to the PCM part as you can see in this plot of a silent bit in the file. DXD original included for reference.

 

But well below audible range ... does it matter?

 

[MarkS]

19 hours ago, Don Hills said:

I am surprised that the MQA decoder doesn't seem to complain when it is fed the invalid compressed data.

 

I agree. These forums indisputedly contain a lot of mixed opinions and judgments regarding MQA, and my personal listening has been generally positive so far, but if MQA can be “faked” that, to me, would be vastly the worst thing I’ve learned/heard yet regarding MQA.  How could that not be a show stopper?

 

 

[FredericV]

This was on public facebook, post shared with public. I first thought I needed new glasses, but no, it's in there:

 

So why not get rid of all those nasty ultrasonics? Yup he wrote it: Mr MQA aka Peter Veth aka Peter Markus, who leads a closed FB group about MQA wrote that MQA works so well because it removes ultrasonics, and as a result sounds better.

He sure must now respect me. My perl script reduces the MQA flac file size to 50% and wav file size to 2/3 and further reduce the presence of ultrasonics that nobody wants
 

[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.

[FredericV]

6 hours ago, miguelito said:

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

How many MQA cd's are there ? 5...10 ?
How many MQA albums on Tidal are there? A few thousand.

While MQA could probably design a different bit allocation scheme for 16 bit distribution files, they also have stated that truncating 24 bit files to 16 bit also works, so Occam's razor dictates they have just truncated the 24 bit version for MQA CD.

It would not make much sense to do such an engineering effort for a few CD's.
 

[mansr]

1 hour ago, FredericV said:

How many MQA cd's are there ? 5...10 ?
How many MQA albums on Tidal are there? A few thousand.

While MQA could probably design a different bit allocation scheme for 16 bit distribution files, they also have stated that truncating 24 bit files to 16 bit also works, so Occam's razor dictates they have just truncated the 24 bit version for MQA CD.

It would not make much sense to do such an engineering effort for a few CD's.

It could be as simple as flipping a setting in the encoder. Or even a setting to have the encoder output both versions at the same time. Until we've had a chance to examine such a CD, we can't know.

[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.

[GUTB]

So, we know that the least 8 bits are ignored by the MQA security algorithm. 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. 

[Don Hills]

50 minutes ago, GUTB said:

So, we know that the least 8 bits are ignored by the MQA security algorithm. 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. 

 

A non-MQA DAC doesn't do the security check, so it won't care how many bits are checked. It's more likely that the reason is to enable downward compatibility for the MQA decoder - so that if the data gets truncated to 16 bits before it reaches the MQA DAC/decoder, it will still play. I think I saw a statement to that effect in one of the MQA docs.

[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.

[GUTB]

1 hour ago, miguelito said:

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

 

It uses data from the control stream and the upper 16 bits, right? There’s no reason why it couldn’t also use the bottom 8 bits. We know that the lower 8 bits is the ultrasonic fold data which means the developers wanted to allow the lower 8 bits to be truncated/discarded for some reason, probably compatibility.

 

BTW, I tried playing the "mqashill.wav" directly over a Plex server from my Technics SU-30G, and while the file is seen by the unit it fails to play it back. If using Roon playing back via a USB link the file will play back and it does show "MQA Studio" on the display.

[Tsarnik]

On Thursday, February 22, 2018 at 4:45 PM, mansr said:

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

Almost got a nervous laughing breakdown.

Thanks Måns! 

[Ralf11]

Think of it as  the “blue light of destiny” ...

[FredericV]

Members of the closed MQA facebook group are asking if this research has been peer reviewed.

It just proves that they are not looking for the truth, but remain in their MQA bubble.

Others have already confirmed on CA that the crippled files authenticate.

Talking to MQA members from the closed group is like talking with flat earthers. They suggested that we contact MQA. They are blind and don't want the truth.