Pro-Ject Pre Box S2 Digital: MQA HW decoding at reasonable cost

[bhobba]

On 13/11/2017 at 6:13 AM, firedog said:

Don’t agree. Lots of DAC designers will tell you that the power supply and analog out section make more difference than the DAC chip. Lots of ESS based DACs sound different, even with the same chip.

 

Abso-friggen-lutely.

 

I know a few DAC designers and that's exactly what they concentrate on.

 

In fact the Grob DAC I posted the review of did exactly that - output - ultra high quality transformer - power supply deveped obver many years to find the best regulator and use them pretty much wherever you need power.

 

Digital power supplies are EVIL.

 

I have an Off-Ramp and it comes with a SMPS the maker claims is the bees knees.  I was with one of those DAC makers and just for the heck of it said lets put the SWMPS on my scope - horrid - that stuff going down the power cable and into the Off-Ramp then radiating about - yuck.   He built a linear supply for me and put that on the scope - dead flat even at maximum sensitivity.  And the difference in sound - easily better.

 

Thanks

Bill

[bhobba]

On 29/10/2017 at 7:05 PM, Miska said:

You mean 2x unfolding followed by 2x upsampling with a poor filter...

 

Ah Miska 

 

Yes - I see your point - but its a bit more nuanced than that.  They don't even reveal what order of spline they use for the downsampling and matching up-sampling - I think it varies and is encoded in metadata.

 

I have heard both the correct unfolding from a  Direct Stream and Explorer 2, and whatever up-sampling Auralic came up with - I cant really say which I prefer.

 

However having your HQPlayer I suspect you might do a better job than the Auralic mob.

 

Thanks

Bill

[bhobba]

On 11/29/2017 at 8:36 AM, mansr said:

MQA "rendering" is a perfectly normal FIR filter (with bizarre coefficients). No splines involved.

 

I think you may know more in the signal processing area than I do.  I am but a humble applied mathematician with an interest in Audio, amongst other things.

 

A spline of order 0 is a rectangle, of order 1 a triangle, and weirder shapes as you go higher - the detail can be found it many books on applied math - its used in many areas - not just signal processing - where curve fitting of some sort is required.

 

Whenever MQA talks about how it does what it does (or others try to explain what they have been told) it talks about using triangle sampling ie a sampling with an order 1 spline:

https://www.soundonsound.com/techniques/mqa-time-domain-accuracy-digital-audio-quality  

 

However as the above says:

Even better results are possible using higher-order ‘B-spline’ kernels, which allow both the position and intensity to be identified of two or more separate pulses occurring within the same sampling period!

 

It is thought, from what others have posted on various forums, that's what they use in practice rather than the triangle and encode in metadata somewhere the right way to decode ie get the best up-sampled approximation from whatever they used to encode it with.  For a spline of order 1 ie a triangle - its dead simple - just linear interpolation.   Higher order splines have other ones.  Naturally its still just a Finite Impulse Responce (ie FIR) filter eg even linear interpretation is just a FIR filter.  It must be FIR because they claim to keep impulse width to a minimum.

 

It's all detailed in their patent:

https://patentscope.wipo.int/search/en/detail.jsf;jsessionid=C54A108611AAB6A34392194DDAEFDDC7.wapp2nA?docId=WO2014108677

 

Why do they do it?  They claim it leads to better impulse responses - the response to a Dirac pulse being only 10us wide using their methods while others ring like a bell.   You of course can use an apodising filter that puts all the ringing after the pulse - that is much better since we are used to hearing ringing after pulses - but before - our ears aren't quite used to that - it never occurs in nature.  Also Dirac pulses do not actually occur in nature (they aren't even actual functions - just some mathematical trickery applied math guys like me use) and if you use a regular linear phase brick-wall filter beyond the highest frequency of actual musical content - nothing happens.  Experiments I have done show in actual material its rare to find stuff above 30k - and even rarer above 50k.  Basically simple 96/24 with a brick-wall filter is all you really need - but that may change in the future as even higher res material becomes available.  I have checked so called 192/24 material from HD downloads - its usually HD ie better than 44.1/16 but 192/24 it mostly isn't - although in a few cases it stands up to scrutiny.  I have one DXD master that goes all the way to 176k- but its the only one I have been able to find.  So IMHO MQA is fixing a problem that doesn't really exist.  What is a problem is the band-witch/size requirements for high res material.   A better way than FLAC to losslessly reduce the size/bandwidth of material is needed.  MQA is one attempt - but IMHO way sub-optimal - better ways exist without detailing them.  

 

The argument over MQA is whether all this 'tom foolery' sounds better.

 

Opinions vary - I like it - others don't.

 

However they make the claim the system with the smallest time domain smear is always preferred - that claim IMHO is utter BS - as I explained with the frequency of actual material.   Also better in audio is a very subjective thing.  I have seen claims like that before, sat with some fellow audiophiles and the opinions usually vary all over the place.  This should be known to Bob Stuart, and I think he does know it, but puts all sorts of marketing spin around it, for reasons that are obvious to anyone with even an inkling of knowledge of how business works.  I am very much a babe in the woods regarding marketing and that other business BS - but even I see whats going on.   Will it succeed - who knows - we will see.

 

At the moment all I can say is I, and pretty much everyone I have listened with, prefer Tidal MQA to Tidal 44.1.  It seems one of those rare things most people I know agree on - like I say its usually all over the place.   But I have seen posts here where others have a different experience - so really its just the people I know - in reality like nearly every other thing in audio its all over the place.

 

What is MQA's advantage then?  Deciding will need much more material with actual content over 50k - and listening tests using that.  Only with such material can the claim of MQA that the recording with the better lime smear is always preferred be put to the test.   My opinion is it will be the same - all over the place - some will say - wow - others blah.

 

Thanks

Bill

[bhobba]

21 minutes ago, mansr said:

A spline is a piecewise polynomial interpolation. A FIR filter is something different. Whereas splines of order 0 or 1 are trivially expressed as FIR filters, higher order splines are not.

 

I know exactly what splines are - they are widely used in applied math.

 

Ok lets take a look at polynomial interpolation - they are FIR:

https://www.dsprelated.com/freebooks/pasp/Lagrange_Interpolation.html

 

Now I haven't seen anything similar for spine interpolation, so I cant be sure in a mathematical sense if its FIR or not, however since the claim of MQA is to reduce time smear as much as possible I cant see how it can be anything but FIR.

 

I frequent a science forum that has some pretty high powered professors etc that post there - I will see what they say and get back.

 

Thanks

Bill

 

 

 

[bhobba]

3 minutes ago, rickca said:

All this discussion of filters belongs in a different thread, please.

 

I will start a new thread with what I find.

 

Thanks

Bill