Jump to content
IGNORED

MQA technical analysis


mansr

Recommended Posts

I'll try to check this on Monday or Tuesday. I need to send the digital capture of the software decoded file because Tidal application enforces hardware decoding when it detects known MQA DAC.

 

The new version of tidal released this week doesn't seem to detect the explorer 2 as mqa dac anymore and passthrough disable will force 2x mode and the mqa light will be off

Link to comment
I thought it is apparent. Same information, but with one extra dimension - time. The Y-axis of mansr's graphics are color-coded and the frequency is swapped to the Y-axis because time is on X-axis.

 

I know how to read the spectrogram, but the conclusions you are able to draw from it and especially that you are able to state it matches the 2 dimension graph is what I'm unable to see at least at a glance. If I can view them both on a computer side by side maybe I can start to see but going back and forth on the phone it's pretty difficult so far.

Link to comment

I have a new nugget of information. MQA places a data stream in bit 8 (i.e. what would be the LSB in 16-bit) of the encoded file. Any claims that undecoded MQA might provide CD quality are thus blatantly false. In fact, this data stream may be in any of bits 8-15 counted from the LSB of 24-bit data, the first being number 0. Higher bits are probably used with 16-bit carriers which are supported by the format though appear not to be deployed at present. All the files I've checked use bit 8.

Link to comment
I have a new nugget of information. MQA places a data stream in bit 8 (i.e. what would be the LSB in 16-bit) of the encoded file. Any claims that undecoded MQA might provide CD quality are thus blatantly false. In fact, this data stream may be in any of bits 8-15 counted from the LSB of 24-bit data, the first being number 0. Higher bits are probably used with 16-bit carriers which are supported by the format though appear not to be deployed at present. All the files I've checked use bit 8.

Thanks for this info (and for all the other great info you've been providing).

 

Apologies in advance if I am being completely dense, but IIRC Stuart/MQA interviews and documents have stated this for some time - that they put a data stream in the LSB of 16-bit in order to preserve compatibility with setups that are limited to 16-bit (as Airplay is, and as Sonos is or used to be, and I gather as at least some forms/tiers of Tidal is?).

 

Or am I missing something obvious and new here? (Which I very well might be!)

Link to comment
Thanks for this info (and for all the other great info you've been providing).

 

Apologies in advance if I am being completely dense, but IIRC Stuart/MQA interviews and documents have stated this for some time - that they put a data stream in the LSB of 16-bit in order to preserve compatibility with setups that are limited to 16-bit (as Airplay is, and as Sonos is or used to be, and I gather as at least some forms/tiers of Tidal is?).

 

Or am I missing something obvious and new here? (Which I very well might be!)

Surely lower 8 bits are used for something. What's the point in having them if it works at 16-bit? Oh well, I'll know soon enough.

Link to comment
Surely lower 8 bits are used for something. What's the point in having them if it works at 16-bit? Oh well, I'll know soon enough.

Oh, I agree completely - wasn't justifying how they've set it up; just was wondering if your new find adds a new wrinkle to what they've previously said about encoding date in the 8th bit.

Link to comment
Oh, I agree completely - wasn't justifying how they've set it up; just was wondering if your new find adds a new wrinkle to what they've previously said about encoding date in the 8th bit.

 

They've constantly been going on about how the undecoded file still has CD quality. I hadn't seen any official statements on exactly which bits they used. Guess they'd rather not talk about that.

Link to comment
I have a new nugget of information. MQA places a data stream in bit 8 (i.e. what would be the LSB in 16-bit) of the encoded file. Any claims that undecoded MQA might provide CD quality are thus blatantly false.

 

Last time, me seems, that even "lossless" term now have more wide meaning: "same level of noise" :)

 

May be I'm wrong. But it is my impression.

AuI ConverteR 48x44 - HD audio converter/optimizer for DAC of high resolution files

ISO, DSF, DFF (1-bit/D64/128/256/512/1024), wav, flac, aiff, alac,  safe CD ripper to PCM/DSF,

Seamless Album Conversion, AIFF, WAV, FLAC, DSF metadata editor, Mac & Windows
Offline conversion save energy and nature

Link to comment
They've constantly been going on about how the undecoded file still has CD quality. I hadn't seen any official statements on exactly which bits they used. Guess they'd rather not talk about that.

 

To be fair they have also consistently talked about the coding space reduction as well, which is what you are referring to. They also claim to use some clever dithering and noise-shaping to regain bit depth lost to using the coding space for other things. Remember that bits 14,15,16 (LSBs in a 16 bit file) aren't used for normal PCM either but should be used for lossy HF encoding (at least for tracks that started of as 88.2 or higher).

Link to comment
To be fair they have also consistently talked about the coding space reduction as well, which is what you are referring to....

 

Not sure I follow - I thought he was talking about how Bob/MQA have put forward the idea that there is no essential difference between a MQA file and the equivalent 16/44 encoding through a "legacy" DAC.

 

They make this claim in the same breadth that they assert a difference in that the MQA file will actually sound better because of the black box magic dust "ADC correction" being sprinkled in it - so its not like they are consistent...

Hey MQA, if it is not all $voodoo$, show us the math!

Link to comment
I found something interesting. The decoder has the provision to swap bits [4:11] and [12:19] in the output and signal to the renderer to reverse this shuffle. If this mode is triggered, only the top 4 bits are passed intact, so while the music would be recognisable, it would sound awful. I don't know what might enable this as I have not seen it with any of the samples I've tested (hardly surprising). Explain how this isn't DRM.

 

I think this deserves more discussion than exactly which bits hold what information.

Link to comment
I think this deserves more discussion than exactly which bits hold what information.

 

Since it appears this discussion is perceived to have legal ramifications, where (IP) will you be taking it?

Hey MQA, if it is not all $voodoo$, show us the math!

Link to comment
The terms imply a delivery method that aims to preserve all information. But MQA has always said that they do not preserve the original input. They apply DSP as part of the recording chain. That DSP is claimed to improve the way the file sounds, by correcting temporal errors. That is their claim. So words such as "lossy" and "lossless" are a little inappropriate ... MQA is always "lossless", but they believe that delivers a better sound. Its lossless in the same way that a crossover is lossless, or DSP room correction.

 

That aside, there are various compression and encoding schemes used by MQA. None are mathematically lossless. Bit depth is always truncated, from a mathematical POV.

 

I know MQA use the word "lossless" (or Bob Stuart has). I believe when pressed he talks about audibly lossless. That's a fair concept, but a lot harder to define and test than mathematical lossless.

 

So are you saying that the better sound supplied by MQA has a form of EQ applied to it?

 

 

Sent from my iPad using Computer Audiophile

Music Server(s): Aurender N100H, Digital to Analog Converter(s): Audio Research DAC 8, Digital to Digital Converter: Bryston BUC-1, Preamplifier: Ayre K-5xeMP, Amplifier(s): Ayre V-5xe, Loudspeakers: Revel Ultima Salon 2, Interconnects: Kimber PBJ, Cardas Clear, Bryston AES/EBU, Loudspeaker Cables: Kimber PR8, Miscellaneous: Oppo BDP 95 disk player, CJ Walker turntable Jelco SA-750D tone arm, Ortofon 2M black cartridge, Magnum Dynalab tuner, Dream System: I've got it!, Headphones: Sennheiser HD600, Grado PS500e, Headphone Amplifier(s):Graham Slee Novo

Link to comment
They've constantly been going on about how the undecoded file still has CD quality. I hadn't seen any official statements on exactly which bits they used. Guess they'd rather not talk about that.

They have talked about it - but I agree with you completely here: You can find almost everything somewhere in MQA's docs or interviews with Stuart, but a lot of it is IMHO not stated clearly, or euphemized with terms that might be accurate technically, but Stuart has to realize also are opaque to many readers.

 

For example, does anyone really think that referring to resolution loss as "coding space reduction" does not function as an obfuscation, at least in the context of mass/prosumer communication?

Link to comment
So are you saying that the better sound supplied by MQA has a form of EQ applied to it?

Sent from my iPad using Computer Audiophile

There is no debate, yes, there has been "EQ", although EQ might be a bit misleading. The signal has had DSP applied, in order to reduce time domain errors. There has also been bit-depth reduction, although this is compensated by noise-shaped dither. The result is mathematically a different signal compared to the original PCM master. But it may be a better sounding signal, or even a more "accurate" representation of the original sound.

 

I guess you could say that MQA tries to anticipate the damage caused by the ADC and DAC and then applies DSP at various stages in the digital chain in order to remove that noise and reproduce the original analog-like sound.

 

Does it work? We have to decide ourselves. That's the consumer's task :) So far, Tidal Masters are sounding rather nice.

Link to comment
[snip]For example, does anyone really think that referring to resolution loss as "coding space reduction" does not function as an obfuscation, at least in the context of mass/prosumer communication?

 

Actually its a pretty accurate way of talking about it. If they are using noise-shaped subtractive dither (the patent mentions this) then its possible to increase apparent resolution while reducing the coding-space for dynamic range. Bob never goes into the details but its clear they are relying on something like this to regain the apparent dynamic range. And I believe they analyze the noise floor of the recording to ensure that there is sufficient bit depth once MQA has been applied. The stereophile Q&A goes into this a little more than the Q&A done here with Bob in April.

Link to comment
There is no debate, yes, there has been "EQ", although EQ might be a bit misleading. The signal has had DSP applied, in order to reduce time domain errors. There has also been bit-depth reduction, although this is compensated by noise-shaped dither. The result is mathematically a different signal compared to the original PCM master. But it may be a better sounding signal, or even a more "accurate" representation of the original sound.

 

I guess you could say that MQA tries to anticipate the damage caused by the ADC and DAC and then applies DSP at various stages in the digital chain in order to remove that noise and reproduce the original analog-like sound.

 

Does it work? We have to decide ourselves. That's the consumer's task :) So far, Tidal Masters are sounding rather nice.

Good post, well said. I do understand the concept; in a way it's similar to HDCD, which encodes the peak-extend and/or filtering info in the LSB (or is it the 2 LSBs) of a CD, reducing the undecoded bit-depth to 14 or 15 bits.

 

I get that MQA is more advanced technology, but plenty of mastering engineers and audiophiles have for years claimed that undecoded HDCDs don't sound quite as good as non-HDCD discs with their full 16-bit resolution.

 

At the very least, I think MQA should be straighter and clearer with folks about exactly what you get if you play an MQA file without a decoder, especially a 16-bit file. I've been struck about how MQA and Stuart seem to communicate either in a hazy nonspecific manner, or a hyper-technical manner. Intentionally or not, they seem to be avoiding hitting the sweet spot of clear, direct, technically substantive explanations.

Link to comment

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now



×
×
  • Create New...