MQA technical analysis

[mansr]

So that also plays differently from mqa dacs ? http://www.computeraudiophile.com/f8-general-forum/big-mqa-news-really-tidal-and-software-decoding-etc-31151/index8.html#post625315

 

There appears to be an option to decode without upsampling. I just haven't figured out how to trigger it yet. Perhaps the exported library interface doesn't make it possible.

[miguelito]

The library contains two functions with names similar to "decode" and "render". I made one test program for each them, storing the output of "decode" in a file. Both functions could of course be called one after the other in a single program, but I wanted to look at the intermediate data anyway.

Yes, as expected. I would think the "decode" func is the same across all implementations whereas the "render" function is tailored to each DAC.

 

My questions are:

1- The plots you show - are they after decode or decode+render?

2- What comes out of decode? PCM?

3- Is the sample rate out of render higher than the 2x you get out of decode?

 

Thx.

[miguelito]

Another one: 0xDECAFBAD.

Bob Stuart's direct deposit account. For convenience.

[mansr]

Yes, as expected. I would think the "decode" func is the same across all implementations whereas the "render" function is tailored to each DAC.

 

My questions are:

1- The plots you show - are they after decode or decode+render?

2- What comes out of decode? PCM?

3- Is the sample rate out of render higher than the 2x you get out of decode?

 

Thx.

 

The set of plots for 2L-048 are all after the decode only. There is also one plot (in reply to Miska) showing render output. The renderer can upsample by 2x or 4x, and also pass the data through unaltered. Again, this might be a limitation of the Bluesound library which only exposes a simplified wrapper around the full MQA software.

[abrxx]

One thing I don't understand: my DAC shows 44.1 or 48 sample rate when playing certain MQA tracks. At least I think it did. But how can that be if the software decoder always upsamples?

[mansr]

One thing I don't understand: my DAC shows 44.1 or 48 sample rate when playing certain MQA tracks. At least I think it did. But how can that be if the software decoder always upsamples?

 

Is 2L-120 (Carl Nielsen Piano Music with Christian Eggen) one of them? It was recorded in 44.1 kHz.

[mm67]

Is 2L-120 (Carl Nielsen Piano Music with Christian Eggen) one of them? It was recorded in 44.1 kHz.

With Explorer2 that track plays at 44.1 or 48 kHz

[mansr]

With Explorer2 that track plays at 44.1 or 48 kHz

 

You mean it indicates that rate. We can't know what it's actually doing internally. What rate does Tidal play that track at with software decode?

[mm67]

You mean it indicates that rate. We can't know what it's actually doing internally. What rate does Tidal play that track at with software decode?

Yes, one one led lights up which indicates 44.1 or 48 kHz operation. Is that track available on Tidal ?

[mansr]

Yes, one one led lights up which indicates 44.1 or 48 kHz operation. Is that track available on Tidal ?

 

https://tidal.com/album/55671890

[Miska]

I have only a rudimentary understanding of the analysis y'all have been doing but this paragraph struck me as odd. Wouldn't this suggest that the noise you are seeing with this MQA decode might be a factor of the track, and not be related to MQA at all. It seems that if you see this behavior with non-MQA content, it would be more likely to be due to some attribute of the track itself (that was carried over into the MQA version) than something inherent to MQA?

 

Well, because it is above Nyquist frequency of the track, it is technically impossible.

 

Let's say you have two tracks in 96/24 format, tracks A and B. Now in this case outputs from the DAC for these tracks differ in frequencies above 48 kHz. And the behavior matches behavior what @mansr presented for the rendering phase.

 

But it could be also a firmware bug in the Meridian DAC that it leaves rendering phase active if the sampling rate is not changed between tracks. I'll check if that's the case...

[mm67]

https://tidal.com/album/55671890

That one plays at 44.1 or 48 kHz through Explorer2, through an other dac using Tidal's software decoder it plays at 88.2 kHz

[mansr]

That one plays at 44.1 or 48 kHz through Explorer2, through an other dac using Tidal's software decoder it plays at 88.2 kHz

 

Thanks for checking. That matches what the Bluesound decoder does.

[smartin]

That one plays at 44.1 or 48 kHz through Explorer2, through an other dac using Tidal's software decoder it plays at 88.2 kHz

 

Yeah, very strange. Using Mytec Brooklyn with passthrough get blue light and 24/44.1. If i disable passthough, it still plays at 24/44.1, but now with a red light (whcih is what happens when Brooklyn is fed software decoded file, it still 'unfolds' fully). However, if I disable MQA decoding on the brooklyn and turn off passthrough, it plays at 24/88.2. That makes no sense...

 

EDIT:

 

In comparison, playing Coltrane's My Favorite Things, all the scenarios make sense. Passthrough with MQA enabled: 24/192, blue light. Disable passthrough with MQA enabled, 24/192, red light. Disable passthrough, disable MQA decoding on Brooklyn, 24/96.

 

Something is funny in the encoding of the Nielsen track, the software and hardware are not seeing the same thing.

[abrxx]

Yeah, very strange. Using Mytec Brooklyn with passthrough get blue light and 24/44.1. If i disable passthough, it still plays at 24/44.1, but now with a red light (whcih is what happens when Brooklyn is fed software decoded file, it still 'unfolds' fully). However, if I disable MQA decoding on the brooklyn and turn off passthrough, it plays at 24/88.2. That makes no sense...

 

EDIT:

 

In comparison, playing Coltrane's My Favorite Things, all the scenarios make sense. Passthrough with MQA enabled: 24/192, blue light. Disable passthrough with MQA enabled, 24/192, red light. Disable passthrough, disable MQA decoding on Brooklyn, 24/96.

 

Something is funny in the encoding of the Nielsen track, the software and hardware are not seeing the same thing.

The difference being that the renderer has to upsample for Coltrane, but seemingly has to downsample for the 2L track. This downsampling is a surprise...it seems to me that the software decoder should not upsample 44.1 or 48kHz material. Perhaps a bug in the software decoder?

 

Would be good to get Bob's input on this.

[mansr]

The difference being that the renderer has to upsample for Coltrane, but seemingly has to downsample for the 2L track. This downsampling is a surprise...it seems to me that the software decoder should not upsample 44.1 or 48kHz material. Perhaps a bug in the software decoder?

 

Would be good to get Bob's input on this.

 

It could also be that the MQA DAC displays the original rate regardless of how it actually goes about playing it.

[smartin]

The difference being that the renderer has to upsample for Coltrane, but seemingly has to downsample for the 2L track. This downsampling is a surprise...it seems to me that the software decoder should not upsample 44.1 or 48kHz material. Perhaps a bug in the software decoder?

 

Would be good to get Bob's input on this.

 

Well, its all 44.1 or 48 to begin with, before it's fed to the MQA decoder. The Coltrane track, with passthrough enabled, but the Brooklyn's MQA disabled, plays as 24/48. If you turn off Tidal's MQA software decode (by disabling exclusive access), and with the Brooklyn's MQA disabled, the track plays at 16/44.1. (EDIT: maybe in this scenario Tidal is streaming the non-MQA file, even though in the app I'm playing the same file?)

[abrxx]

Well, its all 44.1 or 48 to begin with, before it's fed to the MQA decoder. The Coltrane track, with passthrough enabled, but the Brooklyn's MQA disabled, plays as 24/48. If you turn off Tidal's MQA software decode (by disabling exclusive access), and with the Brooklyn's MQA disabled, the track plays at 16/44.1. (EDIT: maybe in this scenario Tidal is streaming the non-MQA file, even though in the app I'm playing the same file?)

 

If you turn off exclusive mode then your sound is routed through the windows or macOs system mixer. That would explain a 16/44.1 output. I don't think that's a valid test: all tests need to be done with exclusive mode on and force volume, so that the DAC gets a bit perfect copy of the TIDAL output.

[mm67]

The difference being that the renderer has to upsample for Coltrane, but seemingly has to downsample for the 2L track. This downsampling is a surprise...it seems to me that the software decoder should not upsample 44.1 or 48kHz material. Perhaps a bug in the software decoder?

Madonnas Like a virgin album also seem a bit odd, Explorer2 leds indicate 172.4 or 192 kHz playback but according to this it was recorded in 16/44.1 or 16/48 format. I thought the name Tidal Masters was referring to offering original masters

[mansr]

Madonnas Like a virgin album also seem a bit odd, Explorer2 leds indicate 172.4 or 192 kHz playback but according to this it was recorded in 16/44.1 or 16/48 format. I thought the name Tidal Masters was referring to offering original masters

 

Archimago has a few words about Tidal's Like a Virgin "master": Archimago's Musings: COMPARISON: TIDAL / MQA stream & high-resolution downloads; impressions & thoughts...

[mm67]

Archimago has a few words about Tidal's Like a Virgin "master": Archimago's Musings: COMPARISON: TIDAL / MQA stream & high-resolution downloads; impressions & thoughts...

 

Yes, I saw that. Funny thing is that MQA version is upsampled even higher than HdTracks version

[abrxx]

Madonnas Like a virgin album also seem a bit odd, Explorer2 leds indicate 172.4 or 192 kHz playback but according to this it was recorded in 16/44.1 or 16/48 format. I thought the name Tidal Masters was referring to offering original masters

Yes that's a bit disappointing. I guess its not MQA's fault but Warners. Given technology to deliver the exact studio master they used an upsample. They may be another explanation but on the face of it it seems that way.

[smartin]

If you turn off exclusive mode then your sound is routed through the windows or macOs system mixer. That would explain a 16/44.1 output. I don't think that's a valid test: all tests need to be done with exclusive mode on and force volume, so that the DAC gets a bit perfect copy of the TIDAL output.

 

That makes sense to explain that one situation, but the rest all follow a logical pattern. Regardless, the hardware MQA is not 'downsampling' in the Nielsen case (not that upsampling is the correct term either for what MQA is doing, or at least purporting to do), rather the software is decoding/unfolding/whatever to 88.2 while the the DACs are not.

 

For the Nielsen MQA album, the software decoder (both Tidal's and BlueSound's which could be the same) and hardware decoders (from both the Meridian and Mytec DAC) are interpreting the metadata differently. One is wrong. I've now checked 20 different tracks (from different albums), none do what the Nielsen tracks do. Considering the 'noise' that started this whole discussion, maybe the difference is due to error handling between the software/hardware decoders? Maybe the hardware decoders fault out if presented with faulty data while the software decoder forges ahead filling in the gaps where errors occur?

[mansr]

That makes sense to explain that one situation, but the rest all follow a logical pattern. Regardless, the hardware MQA is not 'downsampling' in the Nielsen case (not that upsampling is the correct term either for what MQA is doing, or at least purporting to do), rather the software is decoding/unfolding/whatever to 88.2 while the the DACs are not.

 

We don't know that. All we know is what the indicators say. The metadata in the MQA stream probably (I haven't deciphered it yet) includes the original sample rate fed into the encoder. The DAC could be indicating this even if it upsamples/unfolds it to double rate or higher before sending to the DAC chip. After all, something has to upsample it eventually.

 

For the Nielsen MQA album, the software decoder (both Tidal's and BlueSound's which could be the same) and hardware decoders (from both the Meridian and Mytec DAC) are interpreting the metadata differently. One is wrong. I've now checked 20 different tracks (from different albums), none do what the Nielsen tracks do. Considering the 'noise' that started this whole discussion, maybe the difference is due to error handling between the software/hardware decoders? Maybe the hardware decoders fault out if presented with faulty data while the software decoder forges ahead filling in the gaps where errors occur?

 

MQA tracks recorded in 44.1k or 48k are probably quite rare. The Nielsen album is the only one I know of for sure.

[abrxx]

[snip]MQA tracks recorded in 44.1k or 48k are probably quite rare. The Nielsen album is the only one I know of for sure.

 

What about Amy Duncan / Undercurrents ? I thought that was 44.1 MQA.