What is "time resolution"? Options

[Axon]

So I've become involved in a rather colorful argument (I'm Publius in the thread) with somebody on stevehoffman.tv. The original thread revolved around shooting down an old audiophile canard, about how subsample delays cannot be represented in PCM. In the course of that debate, I've begun to question a couple things.

• Is it ever accurate to use the term "time resolution" in any sort of technical context? To the best of my knowledge, it has no universally agreed upon technical definition. Most of the times I've seen it used are either for SACD/DVD-A marketing fluff, or to describe FFT window lengths. I'm tempted to just go quasi-logical-positivist on everybody and say that it is a completely meaningless phrase.
• Is there any meaningful time-domain constraint on audio quality that is directly related to the sampling period? Subsample delays (as I've shown above) are not meaningfully related. Bandwidth is a frequency-domain attribute. Pre-echo potentially gets more audible at lower sampling rates, but this is not a concern with sigma-delta ADCs, and it is of debatable audibility at 44.1 to begin with. Some DSP operations may be harder to implement at lower sample rates, but most of the issues involve seem implementation-related. I'm suspecting that there are no clear general limits as to what can and cannot be accomplished in PCM, except with respect to very domain-specific or system-specific situations; and so any claims of 44khz always being limited in ways different from bandwidth may be regarded with skepticism.

[2Bdecided]

ChiGung,

You can prove sub-sample time domain accuracy using a simple single impulse (or conceptually, a Dirac Delta or Dirac pulse). In a correct system, you can show that the location of the inter-sample peak matches that of the original impulse, even though the pulse itself will be spread out (due to the band limiting).

The reference to periodic functions doesn't mean that sub-sample accuracy doesn't work for any other signal! The sub-sample inter-channel delay of sine waves is a nice example, but you can do just the same thing with a single impulse.

While we're avoiding mathematics, and getting by with examples and hand-waving concepts, consider this: since it works for theoretical infinitely long sine waves, and for theoretical infinitely short impulses, and for practical length "longish" sine waves and for practical length "shortish" impulses (i.e. both theoretical and practical extremes!), that should alert you to the fact that it probably works for any signal in between - including any real world signal.

Cheers,
David.

This post has been edited by 2Bdecided: Oct 6 2006, 10:32

[ChiGung]

We're assuming the signal is band limited, so we absolutely can exactly locate your spike.

You are all assuming that and confidently browbeating with resulting certainties.
It is not a valid assumption > for defining PCMs capabalities of accurately reproducing source.
The term 'source' is meaningless if it cannot differ in detail from 'record'
Of course if the source is known to be bandlimited suitably, the PCM record of it is perfectly complete - there is nothing to discuss in this case. With the precondition that the source is already suitably bandlimited, any samplerate can precisely store any such compliant source -that is not news to me.

I cant believe the loose reasoned, ignorance assuming flack Im taking here....
Corrections about whenever 'jitter' was first transiently refered to in the other thread?

Please gimme a break.

Its probably not worth it for me to explain anything again - cause it will be read with such presumption of error that any realisations possible will not make it from the readers page to their predisposed mind.

...such 'delay' is no definite attribute of the undownsampled source, it is an attribute summed circumspectly from the phases of frequencies surviving the downsample. The frequencies which didnt survive the downsample, contained the information required to resolve the true subsample detail of 'time localised energy spikes'.

How stupid do you guys suppose I am if I was talking about a suitably bandlimited source there? Is it ambiguity about the term 'undownsampled?' -If I meant 'upsampled record' I would could have used that simpler term. Does 'undownsampled source' not translate to 'a source which was not downsampled' -therefore being capable of holding higher frequency detail than the downsampled one? I dont think there is any real ambiguity there, or too much following to figure out what I am actualy talking about.

I am talking about aspects of PCMs resolution of unassumable sources. Like how accurately 16kHz samplerate record could render localised details a 44~kHz record on a CD could render, or how accurately CDs format, could render details which the mastering formats used in production process could render. Why is that a strange interpratation of the term 'resolution' with regads to the capabilities of a digital format?
When you guys ponder the resolution of a digital camera, do you say it perfectly records what it is pointed at if you take pictures out of focus? Yes it might record the 'out of focus picture perfectly precisely', how in focus does the picture need to be before the digitised record of it neccessarily looses information and is therefore an imprecise record of? Most fundamentaly, how accurately can the digitised record be used to render the actual 'scene', with its near infinite complexety emergent from the natural universe?

You know Im obviously talking about somethings which many of you have not considered before. Then you might benefit from reading my points properly instead of the hypercritical attention shown so far.

Good luck with that'

edit: paranoid disambiguations

This post has been edited by ChiGung: Oct 6 2006, 16:37

[krabapple]

I cant believe the loose reasoned, ignorance assuming flack Im taking here....
Corrections about whenever 'jitter' was first transiently refered to in the other thread?

Please gimme a break.

Perhaps it's bias, but I don't see what was either poorly reasoned, or ignorant, about pointing out your mistake re: when jitter entered the SHtv thread.

I am talking about aspects of PCMs resolution of unassumable sources. Like how accurately 16kHz samplerate record could render localised details a 44~kHz record on a CD could render, or how accurately CDs format, could render details which the mastering formats used in production process could render.

All of those sources are bandwidth-limited, of course.

Why is that a strange interpratation of the term 'resolution' with regads to the capabilities of a digital format?
When you guys ponder the resolution of a digital camera, do you say it perfectly records what it is pointed at if you take pictures out of focus? Yes it might record the 'out of focus picture perfectly precisely', how in focus does the picture need to be before the digitised record of it neccessarily looses information and is therefore an imprecise record of? Most fundamentaly, how accurately can the digitised record be used to render the actual 'scene', with its near infinite complexety emergent from the natural universe?

You know Im obviously talking about somethings which many of you have not considered before.

You flatter yourself.

Then you might benefit from reading my points properly instead of the hypercritical attention shown so far.

Good luck with that'

edit: paranoid disambiguations

You don't appear to take correction well. I suggest you get used it...particularly as you've implied, in the SHtv thread, and here, that Nyquist/Shannon is in need of significant revision. That constitutes an extraordinary claim, and you are going to have to present an extraordinarily well-supported case to back it up. And your writing is going to have to be much, much more clear. Good luck with that.

But perhaps for starters, you can describe in much more detail the attributes of the 'unassumable sources' you are talking about. In what sense are they NOT bandlimited?

This post has been edited by krabapple: Oct 6 2006, 16:55

[ChiGung]

But perhaps for starters, you can describe in much more detail the attributes of the 'unassumable sources' you are talking about. In what sense are they NOT bandlimited?

Im not taking criticism well at this point, because Ive been at this for many posts now.
Look. A 44kHz record is bandlimited at 22kHz right? A 22kHz record is bandlimited at 11kHz. A downsample from 44 to 22kHz looses the information for the band 22kHz to 11kHz.....r i g h t ?
If we could all assume that when we downsample, all the information information involved is already suitably bandlimited, that would be an easy world where we could make the claim that 'time resoltuion of PCM' is near as hey perfect -and make it stick. But it is for the very reason that that is an unrealistic assumption, that lowpassing (removing of high frequency energy) is required during good quality downsampling conversion.
Specificaly, yes you can say (and I have said it) that a records information is implicitly bandlimited. But you cannot say that it is therefore bandlimited enough to losslessly survive any following downsamples.

You don't appear to take correction well. I suggest you get used it...particularly as you've implied, in the SHtv thread, and here, that Nyquist/Shannon is in need of significant revision.

I said common reports and opinions drawn from it where.

Trying to get back to the topic>

Ask yourself:
"is there any meaningful space-domain constraint on visual quality that is directly related to the pixel width"

This post has been edited by ChiGung: Oct 6 2006, 17:23