What Sample Rate Do We Really Need?

compact disc, dacs, mp3 players and streaming audio
Erin1
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Re: What Sample Rate Do We Really Need?

Post by Erin1 » 01 Nov 2019 05:57

Hanuman wrote:
29 Oct 2019 14:34
Erin1 wrote:
25 Oct 2019 13:06
In this unlucky example you've given the sampled waveform wouldn't precisely resemble the input waveform... but you're only talking about 4 samples.
It wouldn't matter where, relative to the waveform, the samples are taken. The samples are not the waveform. They are code given to the DAC to enable it to reconstruct the waveform.
Actually it does matter. My answer was in response to someone else's question.
For example if a 22.05khz sine wave audio signal was synced up to an ADC Sampling at 44.1khzt to deliberately sample at the zero crossing of the sine wave, then the ADC would capture silence rather than the 22.5khz sine wave. In the real world this doesn't happen.

NOYB
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Re: What Sample Rate Do We Really Need?

Post by NOYB » 01 Nov 2019 06:46

Erin1 wrote:
01 Nov 2019 05:57
Hanuman wrote:
29 Oct 2019 14:34
Erin1 wrote:
25 Oct 2019 13:06
In this unlucky example you've given the sampled waveform wouldn't precisely resemble the input waveform... but you're only talking about 4 samples.
It wouldn't matter where, relative to the waveform, the samples are taken. The samples are not the waveform. They are code given to the DAC to enable it to reconstruct the waveform.
Actually it does matter. My answer was in response to someone else's question.
For example if a 22.05khz sine wave audio signal was synced up to an ADC Sampling at 44.1khzt to deliberately sample at the zero crossing of the sine wave, then the ADC would capture silence rather than the 22.5khz sine wave. In the real world this doesn't happen.
Cut and paste from a comment to the "Nyquist-Shannon; The Backbone of Digital Sound" video.
https://www.youtube.com/watch?v=pWjdWCePgvA
Jan-Victor Björkqvist2 weeks ago

I don't think it is strictly true that two samples per cycle can reproduce the only signal that lead to those samples. If you sample (with 2 Hz) at 0 s, 0.5 s, and 1 s you will get samples 0, 0, and 0 from a perfect 1 Hz sine wave, i.e. y=sin(2*pi*x). Still, you would obviously also get constant zero samples from having no signal at all, and there is therefore no way to reproduce the original sine wave based on the three samples.
ReaktorLeak2 weeks ago (edited)

You're correct. The theorem states that you can only capture frequencies below the Nyquist frequency (1/2 the sampling rate). It's often misquoted.
But furthermore. If a 22.05 KHz sine wave is getting into 44.1 KHz sampling rate ADC then the low pass filter is broken. At 22.05 KHz the signal level should be below the dynamic range of the bit depth being used.

Erin1
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Re: What Sample Rate Do We Really Need?

Post by Erin1 » 01 Nov 2019 10:20

NOYB wrote:
01 Nov 2019 06:46

But furthermore. If a 22.05 KHz sine wave is getting into 44.1 KHz sampling rate ADC then the low pass filter is broken. At 22.05 KHz the signal level should be below the dynamic range of the bit depth being used.
To be honest, it was simply an example. I'm not sure it would or could occur in real life. I have looked at spectrograms in audio software and seen what appears to be audio frequencies at 22khz, especially on rips of early CDs.

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Re: What Sample Rate Do We Really Need?

Post by Erin1 » 01 Nov 2019 10:22

NOYB wrote:
01 Nov 2019 06:46
[quote=Erin1 post_id=1009386
Anyway, I am not really sure why the concern about sample rates.

If you feel it matters go ahead and buy 96k and 192k music from HD tracks, or record your vinyl at high sample rates.
If not - enjoy CDs or Spotify or whatever.
Ultimately, the only purpose of any recording is to at some later time play it back, so it's about the music. If it's good then enjoy it. If not do something else.

It's somewhat funny the fuss made over audio. I do not know any videophiles that would prefer an analogue VHS tape over Bluray, or DVD for that matter.

I have tried to answer your questions in as much detail as I can (bearing in mind) I am an electronics technician. (But not a mathematical genius) I may have made some linguistic mistakes in my explanations but I am confident my understanding which I've tried to transfer to you is correct.

Is there any agenda here apart from a desire to understand?

Do you have any further unanswered questions?

Hanuman
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Re: What Sample Rate Do We Really Need?

Post by Hanuman » 01 Nov 2019 13:59

Erin1 wrote:
01 Nov 2019 10:22
It's somewhat funny the fuss made over audio. I do not know any videophiles that would prefer an analogue VHS tape over Bluray, or DVD for that matter.
For filmmakers the debate has always been about electronic cameras versus film and there is indeed still a vestigial preference for film.

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Re: What Sample Rate Do We Really Need?

Post by NOYB » 01 Nov 2019 18:57

Erin1 wrote:
01 Nov 2019 10:22
NOYB wrote:
01 Nov 2019 06:46
[quote=Erin1 post_id=1009386
Anyway, I am not really sure why the concern about sample rates.
If what HB says is true. See video links below. Then sample rate does matter. There is apparently more involved here than just the upper frequency limit. For instance. He discusses the time resolution of our auditory system, and the introduction of artifacts due to having such steep LPF so close to the frequencies of interest. Higher sample rates can help in addressing these.

MQA part 1; Why 24 bit 192 kHz audio?
https://www.youtube.com/watch?v=r_wxRGiBoJg

MQA part 2: how does MQA work
https://www.youtube.com/watch?v=T5o6XHVK2HA

The truth about Nyquist and why 192 kHz does make sense
https://www.youtube.com/watch?v=geaoEt-9V-w

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Re: What Sample Rate Do We Really Need?

Post by joedisco » 02 Nov 2019 05:21

This video linked is very informative:

Nyquist-Shannon; The Backbone of Digital Sound
https://www.youtube.com/watch?v=pWjdWCePgvA

And the comments copied from there might need a more thorough approach:
Jan-Victor Björkqvist2 weeks ago

I don't think it is strictly true that two samples per cycle can reproduce the only signal that lead to those samples. If you sample (with 2 Hz) at 0 s, 0.5 s, and 1 s you will get samples 0, 0, and 0 from a perfect 1 Hz sine wave, i.e. y=sin(2*pi*x). Still, you would obviously also get constant zero samples from having no signal at all, and there is therefore no way to reproduce the original sine wave based on the three samples.
First, I think the guy in the "Nyquist-Shannon; The Backbone of Digital Sound" video is doing a great job explaining the NS Theorem (NST) in general terms for the lay person (like me), but as he says somewhere, he is doing some simplifications and some generalizations.

And this is because the NST involves advanced mathematics that can't be crammed into a few minutes video. It takes years for an average intelligent person to reach a level of understanding of advanced mathematics. I, personally, Im certainly not there.

The NST is more complicated than "just sample at twice the highest frequency and go home and be happy and enjoy your 44.1/16 CD music collection". Im afraid it is more complicated than that.

As far as I remember (I might be wrong as Im writting from my memory) there are certain conditions and constraints for the NST to work and you know it is crazy but the NST even goes as far as to state that there are even some specific constraints under which a sample rate lower than the minimum stated by the NST itself can take you to the exact original analog signal.

Now, the zero values:
If you sample (with 2 Hz) at 0 s, 0.5 s, and 1 s you will get samples 0, 0, and 0 from a perfect 1 Hz sine wave
As for the example of the samples taken at exactly zero value so unable to get any information to get back to the original analog signal... Again, as far as I remember, the NST takes into account signal phase. It is not just get some samples no matter what. There are conditions and constraints and there is this thing about signal phase that is considered within the NST.

Ok, I think this adds little to this discussion because Im far from certain about what Im writting here but I just want to point in the right direction. And for me the right direction is that the NST is far more complicated than "just get the minimum stated sample rate and that's it, just get 44.1Khz sample rate and that's all you need to know". There is more to it.

It is somewhat similar to scientists trying to explain Einstein's general relativity theory in which gravity is exemplified by the famous example of the bowling ball and the sheet.... It is just a generalization and there is more to it.

I think, as stated in the video, different mathematicians arrived at the NST independently.

Yes, independently.

We are talking about serious, professional competent people. Not just aficionados. Not just a bunch of Youtubers or Bloggers.

For me it is hard to imagine that all of them failed to consider a very simple circumstance in which samples are taken at exactly zero value. Im sure they thought about it!!

Now, what HB tells us in his video of why 192 Khz matter is interesting but If I understand correctly, he focuses more on the practical side of making use of the NST, it is, the practical aspects of filters and all that.

He worries from the fact that in real life no signal is perfectly bandlimited. And from there, he considers there are problems with the filters and suggests going to a higher sample rate.

From what he says I believe there is some reason to believe that we "need" a higher sample rate but not because the NST does not work but because to take advantage of it and make it work better in real life then we need to go to a higher sample rate. My (perhaps limited) understanding is that this guy HB focuses more on the practical aspects given current technology.

Im not saying he is wrong. Im saying he is focussing on a different aspect of the same problem.

Yes, given current technology, there might be reasons to go to a higher sample rate (192khz) but the benefits might be negligible for most people.

Actually, in real life he mentions that no signal is perfecly bandlimited. And the NST works for bandlimited signals. But this is a theoretical discussion and he attempts to give a practical solution for a theoretical problem.

But in practical sense, does it makes sense?

For some people yes it makes sense as some people are certain that high resolution audio is the way to go. There is even some research that suggest some people can tell HR audio from CD quality. But the same research tells us that these are a minority of people.

Finally, I suggest the following reading, "what the NST says and what it does not say":

https://www.audiostream.com/content/sam ... n-services

Quotes from the article above:

It is a common misconception that the Nyquist-Shannon sampling theorem could be used to provide a simple, straight forward way to determine the correct minimum sample rate for a system. While the theorem does establish some bounds, it does not give easy answers. So before you decide the sampling rate for your system, you have to have a good understanding of the implications of the sampling, and of the information you really want to measure.


The difficulty with the Nyquist-Shannon sampling theorem is that it is based on the notion that the signal to be sampled must be perfectly band limited. This property of the theorem is unfortunate because no real world signal is truly and perfectly band limited. In fact, if a signal were to be perfectly band limited—if it were to have absolutely no energy outside of some finite frequency band—then it must extend infinitely in time.

^That problem with the perfectly bandlimited signal is the one HB mentions in his video... But it is not a reason to consider the NST sample rate is wrong in theoretical terms.

The article adresses the problem of samples taken at zero value...

I believe one must decide to make this discussion either theoretical or practical.

If this is a theoretical question I think there is nothing to add as the NST is fine.

If this is a practical question then there is a lot of discussion to have.

And for some people high resolution is the way to go and for some other people there is no need to go the high resolution way.

At the end, no one is wrong.

Erin1
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Re: What Sample Rate Do We Really Need?

Post by Erin1 » 02 Nov 2019 06:00

NOYB wrote:
01 Nov 2019 18:57
Erin1 wrote:
01 Nov 2019 10:22
NOYB wrote:
01 Nov 2019 06:46
[quote=Erin1 post_id=1009386
Anyway, I am not really sure why the concern about sample rates.
If what HB says is true. See video links below. Then sample rate does matter. There is apparently more involved here than just the upper frequency limit. For instance. He discusses the time resolution of our auditory system, and the introduction of artifacts due to having such steep LPF so close to the frequencies of interest. Higher sample rates can help in addressing these.

MQA part 1;
I have listened to MQA. It sounds like arse to me. It completely messed up the sound. Wrong town in a big way.

I have nothing against high sample rates.
But having personally recorded a lot of vinyl records and analysed the frequency spectrum, I found that very few records have frequencies above 22khz. ( Surprise surprise... Perhaps that's why the 44.1khz sampling rate was chosen for CD 😉)

As for temporal perception, I'm not convinced it actually matters or ads to enjoyment or "natural sound" or however they want to describe it.

If you personally think it matters then do whatever you like.. listen to LPs, mqs, high sample rates, the world is your oyster.

But I think it's just marketing people creating a fear (that your sound is messed up), then presenting a solution...mqa, high sample rates, DSD... And hoping you'll rush out to buy their Kool aid.

So, go right ahead... Buy up big. You'll make those corporations really happy.
Perhaps you'll replace your music collection a second, third, fourth time.

NOYB wrote:
01 Nov 2019 18:57
If what HB says is true.
No, what someone else says is not important. What is important is what you think or feel, based on your experience.
Please do your own listening tests. Please try things for yourself, then comment from your own personal experience.
Last edited by Erin1 on 02 Nov 2019 06:42, edited 4 times in total.

Erin1
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Re: What Sample Rate Do We Really Need?

Post by Erin1 » 02 Nov 2019 06:10

Hanuman wrote:
01 Nov 2019 13:59
Erin1 wrote:
01 Nov 2019 10:22
It's somewhat funny the fuss made over audio. I do not know any videophiles that would prefer an analogue VHS tape over Bluray, or DVD for that matter.
For filmmakers the debate has always been about electronic cameras versus film and there is indeed still a vestigial preference for film.

I'm sorry but I was talking about the home consumer. Find me one person who prefers the quality of VHS over DVD.

Erin1
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Re: What Sample Rate Do We Really Need?

Post by Erin1 » 02 Nov 2019 06:13

Double post

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Re: What Sample Rate Do We Really Need?

Post by joedisco » 02 Nov 2019 06:31

Well, yes, I agree, there are $$$ interests in this issue...
And some marketing is always about fear....
That's too bad, thats sad and thats not ethical....

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Re: What Sample Rate Do We Really Need?

Post by Hanuman » 02 Nov 2019 09:55

Erin1 wrote:
02 Nov 2019 06:10
I'm sorry but I was talking about the home consumer. Find me one person who prefers the quality of VHS over DVD.
Of course nobody does but it's hardly relevant to this discussion because VHS was so manifestly inadequate as a video recording format, being incapable of covering much more than half, if that, of the frequency content of broadcast video.

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Re: What Sample Rate Do We Really Need?

Post by Erin1 » 02 Nov 2019 10:40

Hanuman wrote:
02 Nov 2019 09:55
Erin1 wrote:
02 Nov 2019 06:10
I'm sorry but I was talking about the home consumer. Find me one person who prefers the quality of VHS over DVD.
Of course nobody does
I'm glad we agree
Hanuman wrote:
02 Nov 2019 09:55
but it's hardly relevant to this discussion because VHS was so manifestly inadequate as a video recording format, being incapable of covering much more than half, if that, of the frequency content of broadcast video.
Actually it is very relevant, because we are discussing consumer formats!
Ok, compare it to beta if you like - DVD still wins. Or compare it to broadcast analogue TV - DVD still wins.
Actually, compare to U-matic if you want, but DVD is still better!

Nobody prefers analogue video!
24 frame per second 35mm or 70mm film is excellent, but nobody had that at home!

Hanuman
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Re: What Sample Rate Do We Really Need?

Post by Hanuman » 02 Nov 2019 11:32

Erin1 wrote:
02 Nov 2019 10:40
Nobody prefers analogue video!
Do you think I do?

FYI, video recording formats I've used professionally:

Analogue:

2" Quad
1" C
Betacam
Betacam SP
U-Matic (High Band)

Digital:

D1
D2
Digital Betacam
D5
HDCAM
HDCAM SR
All manner of files created by modern cameras

I get it on the video side - I've been all-digital since 1989. My point is I've never regarded the analogue / digital video transition to be remotely relevant to the audio discussion, either in the studio or in the home. The film to digital camera transition is more relevant.

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Re: What Sample Rate Do We Really Need?

Post by poutrew » 02 Nov 2019 18:20

Erin1 wrote:
25 Oct 2019 12:24
Simple answer:

The low pass filter in the output stage of the DAC will filter out the sharp edges of the stair steps resulting in a smooth analogue sine wave.

Note: only R2R DACs have "stair step" outputs. Newer Delta Sigma DACs don't have stair steps.

It isn't as straight forward as this when dealing with real world circuits that must obey physical law. If you are looking at the DAC output on a scope with a small bandwidth, you will see a nice, pretty sine wave output. But that is only because your scope cant resolve the higher order artifacts that a DAC introduces. Use a high bandwidth scope, and increase the timebase so you can, in effect, drill down into the output signal, and you will be able to see that the pretty output is still stairstep. True, the output filtering makes the output stair curved, but the discretized nature of the signal is still there. No amount of filtering will ever make the output waveform look totally analog. Depending on how high your scopes bandwidth goes, it's interesting to focus in on the output filtered part of the waveform and see all the messy artifacts the DAC introduces into the waveform as it attempts to create a 'clean' output. Now, does all of this really matter? Not to your ears, because some of these artifacts are super high frequency that can extend into the kilo - mega hertz range, and you can not hear it. But it does matter in terms of rfi - radio frequency interference. As a test, stick a portable am radio near the DAC chip when you turn it on and you will be able to hear the spurious crap your 'clean digital sound' actually does generate... lucky we don't have antenna for ears. :)