Understanding the Role of DACs in a Simple Audio Setup

[bigshot]

See the link in my sig, Bit Rate Is Not Resolution

 

[Lohil]

I've had this debate a few times in the past with a few sound engineers on this forum, and I had to conclude that my understanding of "heard it live" was a misconception. It is not as straightforward as it seems if you take the time to consider all factors involved. E.g. placing a stereo microphone at your listening position is not a good place to start, even if that would feel like an intuitive thing to do. There are a number of very good sounding 'single' stereo microphone recordings I have heard, but when I saw how awkwardly the band needed to be arranged around the mic I realised this would not work as a good 'live' performance at all even though the final mix sounded great. It is complicated, that much I know...

Same I have a go to of a particular solo recording of Astrud Gilberto singing quiet nights for testing this sorta stuff, "Someone like you" sung by Doris Day oddly is very good at sounding like she's in the room too, but never heard either of them live so

But even if when one can't hear something very well it in person, I find it has a definition of quality that just isn't present in a reproduction. Not to mention extreme cases like listening to a full orchestra live and being brought to tears, vs. I wonder if I can die from this height boredom of listening to the same recording.

 

[Lohil]

Here a quote about temporal resolution that you may find enlightening. Some people think the temporal resolution of 44.1 kHz 16 bit PCM is 1/44100 but that is not the case, it is much better:



I put a link to the part in one of the xiph videos where timing is covered, just watch 2 minutes from this point:

Right that is a good point, I'm thinking along the lines of a spectra with no limitation of frequencies - but as pointed out for a limited spectral range you can very accurately recreate the timing information in that range.

This would be to the point of the filtering introducing distortion, (which as pointed out is a misnomer albeit splitting of hairs, really what one is doing is just removing higher order components).
The argument I suppose then being well the information I threw away (the super audible high-freq components) were not perceptible anyway, so I've given you both arbitrarily good phase reproduction and all the frequencies you should be able to hear are accurately reproduced - this must be transparent to you yeah , it is certainly a strong and could very well be ultimately the right answer, and if the human body functioned indeed like our digital processing systems irrefutably so, e.g. a 10kilo sample ADC can't tell if a signal was sampled at 50 or 200khz.

But never the less if you were to look at those signals on an oscope and compare a hypothetically infinitely sampled signal vs. one at CD sample rates one would see that difference, so when someone claims to hear that difference and ascribes an ephemeral notion of color to it idk could there be a bio-mechanism by which these seemingly super-audible components can "color" sound in a way which doesn't have a direct mapping to traditional DSP, I leave space for the possibility.

I will also add as a postscript this is all of course in theory, and practically implementing something typically never quite gets to theory... but this has made me curious to see just what the level of distortion is at various sample rates and bit depths on my high speed scope.

 

[gregorio]

It's literally impossible to be more wrong.
Literally every sound in nature is analog.

Oh lord, you can’t even read or understand the definition of analog you yourself quoted.
Acoustic sound is not “a mechanism or device” and the information IS a continuously variable quantity, it is NOT “represented” by one. Sound does not comply with the definition you cited and is therefore NOT analog and anyone with half a brain could work out that the root of the word “analog” is “analogous”: An analogue audio signal is an electrical signal where the voltage is analogous to variations in pressure of a sound wave but sound is NOT analog!

All this time posting in the Sound Science forum and now you’ve proven you don’t even know what sound is, despite the fact we teach that to school children! That’s funny, OMG.

Again, you just love making a fool of yourself.

G

 

[gregorio]

Starting to realize you guys take things very literally / in rigid context

You’re just “starting to realise” what science is, and that this is a science discussion forum, despite already having posted here?

Realistically yes to get that triangle wave I'd need an inf sum of inf. high frequency components which the air would not support, but I could theoretically get something approximating a triangle wave in air though …

You could theoretically but then digital audio is more than capable of representing “something approximating a triangle wave through air”.

and I could also detonate a hand-grenade in the recording studio to get my amplitude spike

You don’t need to detonate a hand-grenade to get an amplitude spike of 10000%, just speak at a normal level in an anechoic chamber. It seems you don’t know what decibels are. And if you detonate a hand-grenade in the recording studio you would NOT be able to “get your amplitude spike” because you would destroy the recording studio’s mics!

Yeah so I have been contextually neglecting the effect the ADC has on the color of sound as well …

An ADC does not “colour the sound”!

for simplicity of argument on just what a DAC would do to sound I'm imaging a digital file taken using an idealized ADC with inf. sampling rate.... but I can understand why that would not be the first place people's minds would go to.

Indeed, no one’s mind here would go to what you’re imagining, in this forum our minds would go to the actual facts/science, as indicated by the name of this forum!

Well so this does answer a lot in where you guys are coming from, which is ult. a totally different direction than my own.

This is the Sound Science forum and if you want to go in a “totally different direction” to the science and actual facts (which is where “us guys are coming from”) then obviously you’re in the wrong place!

I have to say though ult. as I've never heard any audio equipment reproduce sound as though I'd heard it live (what I consider the ult. aim of HiFi) to me the jury is out on how to do that - the DAC (and ADC) apart of that question

Which is it, do you want HiFi or do you want audio equipment to change what it’s reproducing? Regardless of your response though, that is a completely different assertion to the assertion I was responding to, which was: “the jury is still out on what the human ear can hear”, which was false!

As for the paper there is also this one posted http://boson.physics.sc.edu/~kunchu...isalignment-of-acoustic-signals---kunchur.pdf, cited as a sister paper, I don't know if it falls under simular critisism...

It’s the same author with the same lack of knowledge/understanding who has published a few other BS papers, then it’s a reasonable bet. It doesn’t take a genius to work out that in 5us sound travels 0.171 cms, how does that relate to your listening position, do you always listen to your speakers with your head in the same position to within 0.171 cms?

But I totally understand not believing papers (but part of that is being able to peg down what specifically was the inaccuracy/oversight/neglection [i.e. I would be interested in the specific refutation for that paper]), ult. one needs to confirm something for themselves.

Then you’re in the wrong place! I totally do not understand believing papers because belief has nothing to do with the facts/science. The introduction, methodology, results and conclusions of a scientific paper are either valid or invalid and what you choose to believe has no effect on that. And, one does not have to “confirm something for themselves”, I do not have to confirm that I will die if I jump off a skyscraper or measure my terminal velocity. That’s why we have science in the first place, once something is scientifically proven we don’t have to keep confirming it for ourselves. If we did, science would still be back in the Middle Ages and almost no one would ever get beyond 1+1=2!

I'd be surprised if no-one's already done this but you can back of the napkin this yourself, we know (in so far as it is testable claim for yourself, and is relatively non controversial) that the auditory spacial accuracy of a human is about 1 degree (I think) and so you can work out for a given frequency, the distance between the ears and a given spacial target - what the phase accuracy must be of the human ear...
Which I suppose I should work out when I have the time to find a napkin.

Science isn’t defined by what you can do with a napkin! Even if we accept a human discernment of 5us, which isn’t a figure much beyond that which other scientists have demonstrated (under very specific conditions), so what? What has that got to do with digital audio or the typical digital audio format of 16/44.1 ?

G

 

[castleofargh]

Starting to realize you guys take things very literally / in rigid context - which I guess is fair given the context is audio, but, this is just a parenthetical to demonstrate what I was talking about when I said there was no information between sampling points. Realistically yes to get that triangle wave I'd need an inf sum of inf. high frequency components which the air would not support, but I could theoretically get something approximating a triangle wave in air though, and I could also detonate a hand-grenade in the recording studio to get my amplitude spike


Yeah so I have been contextually neglecting the effect the ADC has on the color of sound as well... for simplicity of argument on just what a DAC would do to sound I'm imaging a digital file taken using an idealized ADC with inf. sampling rate.... but I can understand why that would not be the first place people's minds would go to.


Well so this does answer a lot in where you guys are coming from, which is ult. a totally different direction than my own. If a DAC is neutral then the og question is essentially a pointless question. I have to say though ult. as I've never heard any audio equipment reproduce sound as though I'd heard it live (what I consider the ult. aim of HiFi) to me the jury is out on how to do that - the DAC (and ADC) apart of that question

As for the paper there is also this one posted http://boson.physics.sc.edu/~kunchu...isalignment-of-acoustic-signals---kunchur.pdf, cited as a sister paper, I don't know if it falls under simular critisism...

But I totally understand not believing papers (but part of that is being able to peg down what specifically was the inaccuracy/oversight/neglection [i.e. I would be interested in the specific refutation for that paper]), ult. one needs to confirm something for themselves.

I'd be surprised if no-one's already done this but you can back of the napkin this yourself, we know (in so far as it is testable claim for yourself, and is relatively non controversial) that the auditory spacial accuracy of a human is about 1 degree (I think) and so you can work out for a given frequency, the distance between the ears and a given spacial target - what the phase accuracy must be of the human ear...
Which I suppose I should work out when I have the time to find a napkin.

The fundamental rule for sampling is that the signal must be band limited. If you want an unlimited signal, maybe go try some analog recording and playback, and tell us how that went. I guess you'll first need to invent a mic with infinite bandwidth, then invent the rest to match.
Those ideas start to have the sunjam vibe. I really hope I'm wrong.


Papers or beliefs shouldn't be about how we agree with them or not, it should indeed be about how they agree with everything else that has been accepted as factual so far by the science community. Most arguments on the forum are false dichotomies, strawman arguments and irrelevant absolutism, with a generous amount of having to say the opposite of the guy we don't like. Let's not confuse the joy of arguing with research and facts, or assume that somehow truth is a matter of opinion. Opinions are a matter of opinions, and that's the end of the list.

About the discrimination angle, I'm guessing it doesn't work for a bunch of reasons, I'll try to stick with the most obvious:
1/ interaural delay is not a delay on one track/signal.
2/ the brain apparently detects the smallest delays from an envelope type of approach. interaural discrimination exceeds one ear's own temporal and frequency discrimination ability in that one very specific case. So using one to decide what the other is, it just doesn't work.
3/ temporal resolution of a track is not the period of the highest frequency allowed by the sample rate. Having a few people falsely make that argument every other year, including MQA marketing for a while, never made it real.

 

[gregorio]

OP, digital has been perfected in theory for decades.

Yes, nearly 10 decades ago and then it was proven nearly 8 decades ago.

However practical implementation improvements are still ongoing and many of the techniques are not cheap to implement.

Also true, although these “practical implementation improvements” have been beyond the level of audibility for around 3 decades.

For example, military grade ceramic multi layer custom PCB with heavy copper bus is great for reducing noise, jitter etc and can improve all aspects of dac but they are expensive and you won’t find them in less than $20k dacs

They could in theory improve all aspects of a DAC but don’t in practice, the best performing DACs are actually far cheaper, by an order of magnitude or more! And, as these “practical implementation improvements” are inaudible anyway, why would you spend that amount of money even if they were actually an improvement?

For regular folks here is my practical guide on how to tell between the 2 DACs which one is the higher quality. The higher quality dac has the following characteristics:
1. Deeper and greater quality and quantity of sub bass
2. Greater bass weight and slam …

Hang on, a standard cheap DAC, such as a $9 Apple Dongle will reproduce bass and sub bass to a level of accuracy beyond the limits of human hearing. So if a DAC is producing a “deeper and greater quantity of sub bass” or a “greater bass weight and slam” than the accurate amount an Apple Dongle produces, then by definition it must be less accurate and how is a DAC that is less accurate than a $9 DAC “higher quality”? Duh!

Actually, marketing people love “science focused” audiophiles because they can simply order an evaluation board, pop a monolithic dac chip in there, add power supply and case and voila they have a cheap dac that will test great on APx555 and can charge you $500 for it while spending next to nothing on engineering.

You think that “marketing people love” that more than designing a DAC that costs say $100 dollars to make but then charge audiophiles $20,000 for something that according to you is less accurate than a $9 DAC? So, you don’t know anything about DACs or economics! lol

G

 

[eq1849]

Yes, nearly 10 decades ago and then it was proven nearly 8 decades ago.

Also true, although these “practical implementation improvements” have been beyond the level of audibility for around 3 decades.

They could in theory improve all aspects of a DAC but don’t in practice, the best performing DACs are actually far cheaper, by an order of magnitude or more! And, as these “practical implementation improvements” are inaudible anyway, why would you spend that amount of money even if they were actually an improvement?

Hang on, a standard cheap DAC, such as a $9 Apple Dongle will reproduce bass and sub bass to a level of accuracy beyond the limits of human hearing. So if a DAC is producing a “deeper and greater quantity of sub bass” or a “greater bass weight and slam” than the accurate amount an Apple Dongle produces, then by definition it must be less accurate and how is a DAC that is less accurate than a $9 DAC “higher quality”? Duh!

You think that “marketing people love” that more than designing a DAC that costs say $100 dollars to make but then charge audiophiles $20,000 for something that according to you is less accurate than a $9 DAC? So, you don’t know anything about DACs or economics! lol

G

And how exactly are you determining that, practically, DA converters are now perfect?

 

[Lohil]

You’re just “starting to realise” what science is, and that this is a science discussion forum, despite already having posted here?

It’s the same author with the same lack of knowledge/understanding who has published a few other BS papers, then it’s a reasonable bet. It doesn’t take a genius to work out that in 5us sound travels 0.171 cms, how does that relate to your listening position, do you always listen to your speakers with your head in the same position to within 0.171 cms?

Then you’re in the wrong place! I totally do not understand believing papers because belief has nothing to do with the facts/science. The introduction, methodology, results and conclusions of a scientific paper are either valid or invalid and what you choose to believe has no effect on that. And, one does not have to “confirm something for themselves”, I do not have to confirm that I will die if I jump off a skyscraper or measure my terminal velocity. That’s why we have science in the first place, once something is scientifically proven we don’t have to keep confirming it for ourselves. If we did, science would still be back in the Middle Ages and almost no one would ever get beyond 1+1=2!

Science isn’t defined by what you can do with a napkin! Even if we accept a human discernment of 5us, which isn’t a figure much beyond that which other scientists have demonstrated (under very specific conditions), so what? What has that got to do with digital audio or the typical digital audio format of 16/44.1 ?

Well A. I haven't really posted on this forum before - I only posted here to get a 15 post count so I could ask about driver dynamics as they relate to low frequency tone generation, and B. the rigid context would be in how the science is applied - my claim was just that discretizing a real signal (in other-words one which is not band limited) and its reproduction always effects it, it is only a controversial claim in the context of the human hearing. So the response to my original comment I'd expected to be "these effects don't matter to the human ear" not learn Nyquist

The discussion further was basically for me to arrive at this is what people were tying to say, I honestly had no idea there was all this baggage surrounding people making claims about DACs/ADCs (apparently falsely)

As for the timing this translation of distance would be likely be for detecting angle of arrival not lateral translation.

For this last comment we're in half agreement, and it becomes I suppose a philosophical splitting of hairs as I would consider anything which one takes to be true but does not confirm in someway for themselves, to be a belief.

 

[VNandor]

my claim was just that discretizing a real signal (in other-words one which is not band limited) and its reproduction always effects it, it is only a controversial claim in the context of the human hearing.

A real signal is always going to be bandlimited and that is especially true for audio signals because neither the instruments nor the microphones are specifically designed to generate or record anything in the MHz and GHz range. There are some microphones that reach beyond 100kHz but they are not used for studio recordings. This has very little to do with hearing, your claim is wrong to begin with no matter how you slice it.

 

[bigshot]

When you’re sitting on your couch listening to Beethoven’s 7th, the human ear is all that matters.

 

[gregorio]

And how exactly are you determining that, practically, DA converters are now perfect?

How am I determining that digital audio was proposed in theory nearly a century ago? Or how am I determining the performance of a DAC or whether improvements are audible?
The first one is by history, it’s a historical fact that a paper was published in 1927 by Harry Nyquist theorising digital audio.
The second one: A DACs job, as the name indicates, is to convert digital data into an analogue signal, so all we have to do is measure the performance of that conversion process.
The last one: We compare the conversion performance against the laws of physics to determine if imperfections in the conversion can even exist as acoustic sound and if they can, compare that with the established thresholds of human hearing and perform controlled listening tests if necessary.
And lastly, I have not asserted that DACs are perfect, only that they are perfect beyond the level of audibility (unless they’re broken/faulty).

B. the rigid context would be in how the science is applied - my claim was just that discretizing a real signal (in other-words one which is not band limited) and its reproduction always effects it, it is only a controversial claim in the context of the human hearing. So the response to my original comment I'd expected to be "these effects don't matter to the human ear" not learn Nyquist

Please give me an example of a real signal that is not band limited. In addition to instruments and mics being band-limited, as mentioned by VNandor, air itself band-limits any sound wave propagating through it. In addition to the “damping” effect of air that reduces sound level by roughly 6dB per doubling of distance, air also rolls-off high frequencies. For example, a 100kHz sound is rolled-off by about 100dB per 100ft (~3.3dB per meter). In order not to be band-limited, a real sound would have to break the laws of physics!

So, the only question is at what frequency the signal is band limited, not whether it’s band limited and as we’re dealing with human consumers, the obvious frequency would be the threshold of human hearing. Before the advent of digital audio, it was considered that the freq should be around 16kHz, as that is the average threshold for a human adult. Analogue recording media became more unstable/noisy/distorted above 16kHz and indeed, many studio mics were only specified to 14-16kHz, mics which are still in very common use in recording studios around the world today.

For this last comment we're in half agreement, and it becomes I suppose a philosophical splitting of hairs as I would consider anything which one takes to be true but does not confirm in someway for themselves, to be a belief.

The last comment you quoted is not philosophical in the slightest. A human discernment of 5 micro-seconds has nothing whatsoever to do with 16/44.1 (CD format) because the timing resolution of 16/44.1 is roughly 110 pico-seconds, nearly 50,000 times better than the reported human discernment threshold!

G

 

[bigshot]

That's a particularly good one. Bravo!

 

[eq1849]

And lastly, I have not asserted that DACs are perfect, only that they are perfect beyond the level of audibility (unless they’re broken/faulty).

If you have determined, via your test, that a converter is audibly transparent, yet research comes out, peer reviewed research, showing that listeners generally fail blind listening tests, but there are significant differences in the way the brain processes different DACs, then what?

 

[bigshot]

That would be news to me.