Purifi Class D

[mocenigo]

14 hours ago, fas42 said:

 

DACs have historically had a type of distortion which masks low level detail - used to be quite common to remark on how the sound would fall into a "black hole", and that decay tails of instrumental sounds would stop abruptly, not be realistic. I used to shake my head, years ago, at how hopeless the replay on CD systems typically was, on disks I knew  well - literally, half of what was going on, musically, just wasn't there.

 

Which was never measured. And still isn't.

Paint me VERY doubtful but does this distortion really exist? The CD was introduced 50 years ago, if that problem really existed it would have been identified and measured.

[barrows]

19 minutes ago, mocenigo said:

Paint me VERY doubtful but does this distortion really exist? The CD was introduced 50 years ago, if that problem really existed it would have been identified and measured.

Signal correlated noise floor modulation, it has been measured, and better DAC designers are well aware of it. There is another form of artifacts produced by DACs which is also a problem, which I cannot remember the description of, but Bruno Putzeys mentions this other artifact in his comments about the Tambaqui DAC review over at ASR.  He also mentions how to measure this other typical DAC artifact problem.  

So, some of the better DAC designers out there, who also rely on proprietary conversion methods rather than OTS DAC chip solutions, have both identified some of these distortions/artifacts, found a way to measure them, and solved them!  But these do not typically show up in the "standard set" of measurements. 

[PYP]

In this video (starts at 1:40), Eelco Grimm explains their approach to the DAC section of the MU2, which is both a streamer and DAC.  

 

 

 

[PYP]

For those who prefer the read the explanation in more detail:

 

https://www.grimmaudio.com/publications/the-mu2-major-dac/

 

 

[barrows]

21 minutes ago, PYP said:

For those who prefer the read the explanation in more detail:

 

https://www.grimmaudio.com/publications/the-mu2-major-dac/

 

 

Sounds like very similar architecture as the DSC-1/2, and Tambaqui.  Using a discrete FIR DAC for conversion.  Although each system seems to vary a bit in the way the oversampling and modulator is approached (in the Tambaqui onboard and implemented in three powerful DSP chips, in the Grimm an FPGA, and with the DSC-1/2, typically via HQPlayer's wide variety of modulators and filters).  Grimm's 11th order modulator seems like it might be unique.

Would love to see what @muski, Jussi, might have to say RE, Grimm's approach, and the noise profiles shown in the link.

 

Just realized we are way off topic for this thread, oops!  But the discussion is interesting, maybe we should move it somewhere else?

[DuckToller]

8 minutes ago, barrows said:

Would love to see what @muski, Jussi, might have to say RE, Grimm's approach, and the noise profiles shown in the link.

@Miska???

[barrows]

6 minutes ago, DuckToller said:

@Miska???

Goops, sorry @muski, of course I meant @Miska (Jussi).  Thanks for pointing this out!

[PYP]

41 minutes ago, barrows said:

Sounds like very similar architecture as the DSC-1/2, and Tambaqui.  Using a discrete FIR DAC for conversion.  Although each system seems to vary a bit in the way the oversampling and modulator is approached (in the Tambaqui onboard and implemented in three powerful DSP chips, in the Grimm an FPGA, and with the DSC-1/2, typically via HQPlayer's wide variety of modulators and filters).  Grimm's 11th order modulator seems like it might be unique.

Would love to see what @muski, Jussi, might have to say RE, Grimm's approach, and the noise profiles shown in the link.

 

Just realized we are way off topic for this thread, oops!  But the discussion is interesting, maybe we should move it somewhere else?

MU2 info under the MU1 thread for now (see last few pages):

 

 

[mocenigo]

1 hour ago, barrows said:

Signal correlated noise floor modulation, it has been measured, and better DAC designers are well aware of it. There is another form of artifacts produced by DACs which is also a problem, which I cannot remember the description of, but Bruno Putzeys mentions this other artifact in his comments about the Tambaqui DAC review over at ASR.  He also mentions how to measure this other typical DAC artifact problem.  

So, some of the better DAC designers out there, who also rely on proprietary conversion methods rather than OTS DAC chip solutions, have both identified some of these distortions/artifacts, found a way to measure them, and solved them!  But these do not typically show up in the "standard set" of measurements. 

Ok I am aware of these. Fas42 mentioned factors that have never been measured, which is of course nonsense. Today’s DACs can probably pass a zero test with a 20 bit signal.

[mocenigo]

2 hours ago, barrows said:

Signal correlated noise floor modulation, it has been measured, and better DAC designers are well aware of it. There is another form of artifacts produced by DACs which is also a problem, which I cannot remember the description of, but Bruno Putzeys mentions this other artifact in his comments about the Tambaqui DAC review over at ASR.  He also mentions how to measure this other typical DAC artifact problem.  

So, some of the better DAC designers out there, who also rely on proprietary conversion methods rather than OTS DAC chip solutions, have both identified some of these distortions/artifacts, found a way to measure them, and solved them!  But these do not typically show up in the "standard set" of measurements. 

Both signal correlated noise and idle tones are a solved problem in the recent multi-bit delta-sigma DACs. But in 2013, when Bruno started designing his DAC, they were still a problem. 
 

And they show up as distortion (mostly in IM spectra with only a few tones) and spikes in noise, respectively, provided the measurement equipment is sufficiently resolving.

 

[fas42]

6 hours ago, mocenigo said:

Ok I am aware of these. Fas42 mentioned factors that have never been measured, which is of course nonsense. Today’s DACs can probably pass a zero test with a 20 bit signal.

 

They are not measured for the benefit of the consumer. Of course there have always been designers and builders of audio components who understand that better techniques are needed to make items like DACs function more accurately. But the potential purchaser has no idea which is superior in this area, by the way of numbers - handwaving by the company marketing, and review ticks by people who try them is about as good as it gets; you can't decide which is better by looking at a specifications page.

[mocenigo]

19 minutes ago, fas42 said:

They are not measured for the benefit of the consumer.

 

This is not what you said. You are changing your story. You said that these are not measured or we do not know how to.

 

19 minutes ago, fas42 said:

Of course there have always been designers and builders of audio components who understand that better techniques are needed to make items like DACs function more accurately.

 

Of course.

 

19 minutes ago, fas42 said:

But the potential purchaser has no idea which is superior in this area, by the way of numbers - handwaving by the company marketing, and review ticks by people who try them is about as good as it gets; you can't decide which is better by looking at a specifications page.

that’s why there have been independent reviewers, and some, like ASR, give you proper noise profiles (then you can see idle noise) and multitone distortion (that contains also the signal modulated noise, so it can be used to bound this).

 

Let us face it, most people would not know how to read those measurements (and that’s why most ASR readers are just fine with the SINAD, that is just ONE data point out of thousands) but the data is there.

[fas42]

44 minutes ago, mocenigo said:

 

This is not what you said. You are changing your story. You said that these are not measured or we do not know how to.

 

Well, we can get into arguments about precision of words used, but what's the point of that? I said "DACs have historically had a type of distortion which masks low level detail" and "Which was never measured. And still isn't." The intent of what I was saying is that the purchasers are not made aware of the possible, highly important, improvement to a DAC they're looking at, by it being part of the standard way of describing its performance, say, "Noise modulation factors = -90dB".

 

44 minutes ago, mocenigo said:

 

Let us face it, most people would not know how to read those measurements (and that’s why most ASR readers are just fine with the SINAD, that is just ONE data point out of thousands) but the data is there.

 

The data may be there, but there should be something like at least a single number as part of specs, which gives an indicative measure of how well engineered the product is, in this regard.

[mocenigo]

1 hour ago, fas42 said:

 

Well, we can get into arguments about precision of words used, but what's the point of that? I said "DACs have historically had a type of distortion which masks low level detail" and "Which was never measured. And still isn't."

 

ok, here I can say we agree except for the last sentence.

 

1 hour ago, fas42 said:

The data may be there, but there should be something like at least a single number as part of specs, which gives an indicative measure of how well engineered the product is, in this regard.

well, that value exists, mostly, and is THD+N (aka SINAD) — even when it is given at 1khz only, I would argue that it would be a weird effort to design a DAC that is excellent at 1khz and bad at 200hz or 5khz. Some correlation between these values must exist. Some manufacturers give the value A-weighted, so it is not only at 1khz.
 

Also, that value is an upper bound to distortion and to noise. Even though the first is harmonic distortion, we know that THD and IMD are correlated, so am exceptionally good value of the first implies at least a very good one of the second. Regarding noise, if it is computed over the whole audible spectrum, it covers also idle tones — that in some Δσ DACs of the ‘90s that were probably used also a bit later, were eating up to three least significant bits of a 16bit sample. But if you see a noise value of -120Db you know that idle tones are not audible.

 

I wish companies would agree to show THD+N either as a bound over the audible spectrum or A-weighted. But of course you know that it’ll be precisely the “hiend” audiophile manufacturers that will oppose it.

 

Hence , the question is, how do we get manufacturers to use it consistently?

[fas42]

12 hours ago, barrows said:

Signal correlated noise floor modulation, it has been measured, and better DAC designers are well aware of it. ...

 

Somewhat amusing ... I typed, "Signal correlated noise floor modulation", as a phrase into Google Search - and it's so well known that your use just now of this term is the lone example of this, a single hit only, on the net ...

[Jud]

39 minutes ago, fas42 said:

 

Somewhat amusing ... I typed, "Signal correlated noise floor modulation", as a phrase into Google Search - and it's so well known that your use just now of this term is the lone example of this, a single hit only, on the net ...

 

🙄

 

Read and learn, Frank:

 https://users.ece.utexas.edu/~bevans/courses/rtdsp/lectures/10_Data_Conversion/AP_Understanding_PDM_Digital_Audio.pdf

[fas42]

41 minutes ago, Jud said:

 

🙄

 

Read and learn, Frank:

 https://users.ece.utexas.edu/~bevans/courses/rtdsp/lectures/10_Data_Conversion/AP_Understanding_PDM_Digital_Audio.pdf

 

And pray, what in that document has anything to do with "Signal correlated noise floor modulation" ... hmmm??

 

What it is about, is,

 

Quote

This document will cover the basics of PDM: how it is generated, transmitted, and manipulated.

 

as compared to,

 

Quote

Most current digital audio systems use multi-bit PCM (pulse code modulation) to represent the signal.

 

[Jud]

1 hour ago, fas42 said:

 

And pray, what in that document has anything to do with "Signal correlated noise floor modulation" ... hmmm??

From the very first page after the table of contents, in the glossary of terms that are defined at the outset so you will be able to understand what's being discussed in this monograph from Audio Precision on understanding digital audio:

 

"Noise modulation is the undesirable variation of the noise floor in a system due to the signal content."

 

So I guess this concept you're laughing off is something experts consider important for understanding digital audio. If you'd prefer not to have a better understanding of digital audio, that's of course up to you.

[fas42]

22 minutes ago, Jud said:

From the very first page after the table of contents, in the glossary of terms that are defined at the outset so you will be able to understand what's being discussed in this monograph from Audio Precision on understanding digital audio:

 

"Noise modulation is the undesirable variation of the noise floor in a system due to the signal content."

 

So I guess this concept you're laughing off is something experts consider important for understanding digital audio. If you'd prefer not to have a better understanding of digital audio, that's of course up to you.

 

Okay, to me, "Noise modulation is the undesirable variation of the noise floor in a system due to the signal content" == "Signal correlated noise floor modulation" ... different ways of saying, apparently, the same thing. And the document then goes on to say, that it's all about dither, to 'solve' it. Dither has been around since the earliest days of digital - is this what barrows is talking about?

[Jud]

5 hours ago, fas42 said:

 

Okay, to me, "Noise modulation is the undesirable variation of the noise floor in a system due to the signal content" == "Signal correlated noise floor modulation" ... different ways of saying, apparently, the same thing.
 

 

Bingo. We've gone from "No one ever mentions this" to "This document doesn't talk about it," to "The document talks about exactly this."

 

5 hours ago, fas42 said:

And the document then goes on to say, that it's all about dither, to 'solve' it. Dither has been around since the earliest days of digital - is this what barrows is talking about?

barrows didn't mention solutions, just said DAC designers were well aware of it. Whatever solutions he may know about or want to discuss are up to him. But can we now stop this business of trying to derail potentially useful and informative contributions by others?

[fas42]

10 hours ago, Jud said:

 

barrows didn't mention solutions, just said DAC designers were well aware of it. Whatever solutions he may know about or want to discuss are up to him. But can we now stop this business of trying to derail potentially useful and informative contributions by others?

 

Sometimes, it appears that one has to spell things out, ... let's see now, try guessing whether I'm trying to stop barrows from contributing very useful info, or, I'm "somewhat amused" that the subject is so little debated that it's impossible to find another reference to the matter, or that it's a "dark secret" whose name shall not be breathed ...

 

Interesting that some need to believe that people have a desire to have to go at another person, rather than saying something which is expressing amusement at an overall situation.

 

 

[kumakuma]

38 minutes ago, fas42 said:

 

Sometimes, it appears that one has to spell things out, ... let's see now, try guessing whether I'm trying to stop barrows from contributing very useful info, or, I'm "somewhat amused" that the subject is so little debated that it's impossible to find another reference to the matter, or that it's a "dark secret" whose name shall not be breathed ...

 

Interesting that some need to believe that people have a desire to have to go at another person, rather than saying something which is expressing amusement at an overall situation.

 

 

You found only one reference because you put a very specific phrase into Google with quotes around it.

 

Use Google properly and you'll find many references to the subject in question.

 

 

[fas42]

25 minutes ago, kumakuma said:

 

You found only one reference because you put a very specific phrase into Google with quotes around it.

 

Use Google properly and you'll find many references to the subject in question.

 

 

 

Attempting to do things with a light touch is very dangerous near audiophiles  ... "signal correlated noise floor modulation" is a pretty obvious way to describe what's going on; I've had much discussion with other audio people about this sort of behaviour, elsewhere, where they used this type of expression - yet, this is the first time that this precise sequence of words registered on the net ...

 

"dac noise modulation", no quotes, picks up a whole array of stuff, and, dare I say it, first call is the website that shall not be named - Amir "proves" that the whole thing is hogwash anyway, using, gasp!, measurements ... has the audio world moved on, to accept these ideas, or not?

 

https://www.audio “science” review/forum/index.php?threads/dac-noise-modulation-chord-dave-vs-topping-dx7-pro.37119/

[fas42]

"Noise modulation" with whatever words you wish to add to express the situation more precisely seems to have only really been 'sorted' to a better level, quite recently - I recall my audio show some 8 years ago, where in a room which did do better, overall, compared to the others there, a flavour of the day Benchmark DAC was used, and that setup suffered from the usual "where's the detail gone?!" issue - better than the worst of them, but still a way to go ... show of only some weeks ago showed a welcome lift of the standard, in general; so, progress was made.

 

Overall, controlling noise wherever it arises is the bugbear in audio chains - my experiences have shown that it is possible to get on top of it without diving deep into the heart of the DAC workings; but, ultimately the solution chosen is up to the individual ...

[botrytis]

56 minutes ago, fas42 said:

"Noise modulation" with whatever words you wish to add to express the situation more precisely seems to have only really been 'sorted' to a better level, quite recently - I recall my audio show some 8 years ago, where in a room which did do better, overall, compared to the others there, a flavour of the day Benchmark DAC was used, and that setup suffered from the usual "where's the detail gone?!" issue - better than the worst of them, but still a way to go ... show of only some weeks ago showed a welcome lift of the standard, in general; so, progress was made.

 

Overall, controlling noise wherever it arises is the bugbear in audio chains - my experiences have shown that it is possible to get on top of it without diving deep into the heart of the DAC workings; but, ultimately the solution chosen is up to the individual ...

Memory is a fickle thing - it is wrong most of the time because every time you access that memory it is modified and put back into place. So this is a probably not story.