IPB

Welcome Guest ( Log In | Register )

7 Pages V  < 1 2 3 4 > »   
Reply to this topicStart new topic
What is "time resolution"?
krabapple
post Oct 6 2006, 21:11
Post #26





Group: Members
Posts: 2241
Joined: 18-December 03
Member No.: 10538



QUOTE (ChiGung @ Oct 6 2006, 12:08) *
QUOTE
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.



All you need to show, then, is either that

1) for digital audio generally at whatever chosen sample rate: there is information *originally within the band* that necessarily gets excluded by the bandlimiting requirement, and thus becomes unrecoverable

or

2) for redbook PCM specifically: the 22 kHz bandlimit is insufficient to capture what is audible in your unassumable sources -- which translates to, showing that there is audible information above 22 kHz in either
live recordings, or analog tape sources.


(And reconcile them with these facts: all recording and playback methods are bandlimited. And all hearing is bandlimited too.)

So good luck with that.


QUOTE
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.


Hold on... are you defining 'lossless' perceptually, or strictly in terms of data? If you 'lose' frequencies that cannot be heard, the downsample is technically lossy, but not perceptually.

This post has been edited by krabapple: Oct 6 2006, 21:25
Go to the top of the page
+Quote Post
Canar
post Oct 6 2006, 21:20
Post #27





Group: Super Moderator
Posts: 3358
Joined: 26-July 02
From: princegeorge.ca
Member No.: 2796



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


Your analogy is flawed. Drop the analogy and you might start to understand. All that sampling rate / pixel width does is limit the frequency of the signal that can be encoded. It says nothing about the phase of the signal. Phase is not really visually perceptible. Time resolution (ie. phase in a sense, and also subsample delay) is a function of both the bit depth and the sampling rate, not just the sampling rate.

This post has been edited by Canar: Oct 6 2006, 21:21


--------------------
You cannot ABX the rustling of jimmies.
No mouse? No problem.
Go to the top of the page
+Quote Post
kwwong
post Oct 7 2006, 05:12
Post #28





Group: Members
Posts: 113
Joined: 28-December 05
Member No.: 26686



QUOTE (ChiGung @ Oct 5 2006, 18:57) *
QUOTE (kjoonlee @ Oct 6 2006, 00:47) *
Does "higher sampling rates mean higher temporal resolution" count?

Apparently not.


Apparently yes.. For a fixed frame size, sampling rates can have an effect on temporal resolution.

Actually, time resolution exists in trade-off with frequency resolution. The higher the time resolution, the lower the frequency resolution and vice-verse.
Go to the top of the page
+Quote Post
Canar
post Oct 7 2006, 08:04
Post #29





Group: Super Moderator
Posts: 3358
Joined: 26-July 02
From: princegeorge.ca
Member No.: 2796



Exactly, kwwong. ChiGung, consider this: In the context of your video/audio analogy there is no maximum frequency for video. We do not use a format that arbitrarily limits our sampling frequency (ie. pixel width) in video. 640x480 has, relatively, higher frequency than 320x240. We can perceive that difference easily. We cannot perceive increases in audio bandwidth, as our ears are physically limited to (populistically speaking) 20KHz or so. Below that frequency, we have complete frequency reproduction (according to Nyquist) within a certain signal to noise ratio. Increases in time resolution imply increases in sampling frequency. Below half the sampling frequency, all timing details are perfectly coded (provided technical competence).

This post has been edited by Canar: Oct 7 2006, 08:05


--------------------
You cannot ABX the rustling of jimmies.
No mouse? No problem.
Go to the top of the page
+Quote Post
MedO
post Oct 7 2006, 10:43
Post #30





Group: Members
Posts: 341
Joined: 24-August 05
Member No.: 24095



QUOTE (ChiGung @ Oct 6 2006, 18:08) *
Look. A 44kHz record is bandlimited at 22kHz right?

Right.
QUOTE (ChiGung @ Oct 6 2006, 18:08) *
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 ?

Yes. Frequencies present above 11khz will have to be filtered out before downsampling and cannot be preserved in this case.
I don't think anyone here assumed downsampling is always lossless.

QUOTE (ChiGung @ Oct 6 2006, 18:08) *
Ask yourself:
"is there any meaningful space-domain constraint on visual quality that is directly related to the pixel width"


No, there isn't. You can have peaks in image data at any(*) position between the pixels.

*assuming arbitrary bitdepth.

This post has been edited by MedO: Oct 7 2006, 10:44
Go to the top of the page
+Quote Post
cabbagerat
post Oct 7 2006, 18:00
Post #31





Group: Members
Posts: 1018
Joined: 27-September 03
From: Cape Town
Member No.: 9042



QUOTE (MedO @ Oct 7 2006, 01:43) *
No, there isn't. You can have peaks in image data at any(*) position between the pixels.

*assuming arbitrary bitdepth.
That assumption is a bit of a problem, in my mind. As has been mentioned earlier in the thread, there is a relationship between sampling rate, bit depth and maximum temporal resolution (or phase resolution). If you define maximum phase resolution as the minimum difference in phase that can be resolved, then it's a fairly straight forward calculation can be used to set a limit on the resolution.

A little playing with the numbers suggests that the maximum phase resolution of 44100 16bit PCM is on the order of 6e-9 wavelengths. I would bet a case of beer that this effect is inaudible.


--------------------
Simulate your radar: http://www.brooker.co.za/fers/
Go to the top of the page
+Quote Post
MedO
post Oct 7 2006, 18:42
Post #32





Group: Members
Posts: 341
Joined: 24-August 05
Member No.: 24095



QUOTE
That assumption is a bit of a problem, in my mind. As has been mentioned earlier in the thread, there is a relationship between sampling rate, bit depth and maximum temporal resolution (or phase resolution). If you define maximum phase resolution as the minimum difference in phase that can be resolved, then it's a fairly straight forward calculation can be used to set a limit on the resolution.

A little playing with the numbers suggests that the maximum phase resolution of 44100 16bit PCM is on the order of 6e-9 wavelengths. I would bet a case of beer that this effect is inaudible.


Of course there is a limit. If there wasn't, you could store an infinite ammount of information in the exact position of that peak. Turning this the other way, you cannot store audio data in a way which completely preserves this information. However, the way it is it should be accurate enough. My point was that you can place your "brightness-peak" on a great number of positions between the pixels.

This post has been edited by MedO: Oct 7 2006, 18:42
Go to the top of the page
+Quote Post
cabbagerat
post Oct 7 2006, 20:57
Post #33





Group: Members
Posts: 1018
Joined: 27-September 03
From: Cape Town
Member No.: 9042



QUOTE (MedO @ Oct 7 2006, 09:42) *
Of course there is a limit. If there wasn't, you could store an infinite ammount of information in the exact position of that peak. Turning this the other way, you cannot store audio data in a way which completely preserves this information. However, the way it is it should be accurate enough. My point was that you can place your "brightness-peak" on a great number of positions between the pixels.
Well, I hadn't thought of it in the context of information storage, but that's a very nice way to visualize the limit. I would imagine that this is certainly not one of the limiting factors on the quality of digital storage, but there are certainly people who would say otherwise. You can't really pretend that any mechanical analog system (tape, vinyl, etc) could do better.


--------------------
Simulate your radar: http://www.brooker.co.za/fers/
Go to the top of the page
+Quote Post
ChiGung
post Oct 7 2006, 23:18
Post #34





Group: Members
Posts: 439
Joined: 9-February 05
From: county down
Member No.: 19713



QUOTE (MedO @ Oct 7 2006, 09:42) *
Of course there is a limit. If there wasn't, you could store an infinite ammount of information in the exact position of that peak. Turning this the other way, you cannot store audio data in a way which completely preserves this information. However, the way it is it should be accurate enough. My point was that you can place your "brightness-peak" on a great number of positions between the pixels.

What is 'accurate enough' is a different matter id not like to confuse the main investigation with.

The situation is, that the positioning of the brightness peak in the record is limited by the fact that the record has an implicit bandlimit. The position of the brightness peak in the source image is not implicity restricted by this limitation. (edit: yes the peak could be precisely positioned if we could employ all of the information stored in surrounding samples to do so - but all those other samples have information of their own to carry*) .

Depending on the characteristics of the information conveyable from the origional media (lenses, microphones, physics of air etc) it may be suitably restricted for precise capture/repoduction by certain samplerates, but because the source media may also not be suitably restricted (and very often is not) we have to allow for this possibility. It's surprised me that there has been a strong tendency to discount this as recognising source media may have finer resolution than target samplerates is fundamental to sensible statements of how accurately target samplerates can record the information of various sources.

Back to the 'peak of brightness', or 'peak of level' example (whichever is easier to visualise) The position of the peak in the source image or sound will in almost all cases be altered by the lowpass of conversion.
The record will then indicate a very precise position, but its disagreeance with the source will be unknown, the precise position of the peak in the source may be anywhere between the enclosing sample points

Then this makes clear my objection to stating the time resolution of PCM as near perfect. That the position in time of any time-localisable details, like peaks, attacks, cliffs etc, cannot be known to agree with the position of such details in the source, except when we can assume convienient limitations of the source. >A clause which basicaly passes on the limitations of the PCM record, to the source record. That is if we assume the source and the records limitations are the same, then to determine the accuracy limitations of the record, we must determine the limitations of the source. Only then can it be said that the record has no limitations with regards the assumable source. It becomes a confusingly convoluted case.

Another way of stating the case, is that the gaps between the samples, embody the unstateable frequencies above the implicit bandlimit. (By implicit bandlimit I mean to imply the one enforced by the nyquist frequency cuttoff, not arbitrary ones which may or may not have been applied on the record by extra conditioning)

Regarding the validity of the 'screen resolution' metaphor; when it was introduced earlier this reminder was made: -
QUOTE
(note that regardless of the quality of anyones particular video card system, bandlimited 'acoustic type' interpolation can be applied to visual data as well as audio (and is a rather good way to treat it, if not the optimal (?))


In other words it can be a fair, almost identical analogue, but if its not accessible to some, they may just have to try to skip over it.

Id remind again, that phase never indicates a point in time, it indicates conditions of a period located throughout time. So the fact that phase can be stated in a record quite precisely, does not mean any real position in time can be stated in the record as precisely.

Some are refering to limits of perceptability which are only discernable with physiological experimentation, limits of technical capability are not affected by what it is possible to hear or see.

Other queries have been raised all of which I hope the answers to will become clear, when the overall matter is realised shifty.gif

I exhibited some more underdog fatigue earlier blush.gif Im glad to see that did not harm anyones curiosity.

best regards'

...............
extras

This post has been edited by ChiGung: Oct 8 2006, 00:20


--------------------
no conscience > no custom
Go to the top of the page
+Quote Post
MedO
post Oct 8 2006, 00:13
Post #35





Group: Members
Posts: 341
Joined: 24-August 05
Member No.: 24095



QUOTE (ChiGung @ Oct 8 2006, 00:18) *
the precise position of the peak in the source may be anywhere between the enclosing sample points -as confirmed by med0.

Please don't misquote me. I said that it is possible to record the position of a peak in a bandlimited signal even if the peak is between two samples, but the precision will be limited (as in "Bill Gates has a limited ammount of money").

If you sample at 1hz (and your signal is limited to 0.5hz), you can record and reconstruct a signal with a peak at 5.23 seconds. If you used a low bitdepth, the peak may be shifted a bit (like 0.01s). If you used a high bitdepth, the position of the peak will be more precise. The point I was making was, you cannot have *infinite* precision. But you can get pretty close. cool.gif
Go to the top of the page
+Quote Post
Canar
post Oct 8 2006, 00:26
Post #36





Group: Super Moderator
Posts: 3358
Joined: 26-July 02
From: princegeorge.ca
Member No.: 2796



ChiGung, it is increasingly apparent you are not investing any effort in trying to understand what we are saying. I am not unused to this behaviour from you. I will try something concrete to show you what we are saying, then I advise that people stop posting here. This is a foolish response to trolling that is solved by a little bit of focused EE research on CG's part.

Consider a sine wave at a frequency 22050-(1/32768) Hz, perfectly encoded in 44.1KHz/16bit CD Audio. Nyquist's theorem proves that this can be perfectly encoded. This should have the property that (edit: the absolute value of) each successive sample is a single number smaller than the previous. Given a certain phase shift, 2^15 samples should have the form (-32768,32767,-32766,32765,...,0). This has an interesting property: every other 16-bit value represents a different phase shift! It may seem counter-intuitive, but such a data set does not decrease in volume, provided accurate reproduction. That means that for such a high-frequency value, the "time resolution" is essentially 2^15 times greater than the sampling frequency. I would suppose the maximum time resolution of the CD audio format to be something near that value, though it is possible that the upper maximum could be 2^16.

This post has been edited by Canar: Oct 8 2006, 01:02


--------------------
You cannot ABX the rustling of jimmies.
No mouse? No problem.
Go to the top of the page
+Quote Post
ChiGung
post Oct 8 2006, 00:28
Post #37





Group: Members
Posts: 439
Joined: 9-February 05
From: county down
Member No.: 19713



QUOTE (MedO @ Oct 8 2006, 00:13) *
QUOTE (ChiGung @ Oct 8 2006, 00:18) *
the precise position of the peak in the source may be anywhere between the enclosing sample points -as confirmed by med0.

Please don't misquote me. I said that it is possible to record the position of a peak in a bandlimited signal even if the peak is between two samples, but the precision will be limited (as in "Bill Gates has a limited ammount of money").

Im sorry I did misquote you, I was just in the process of editing it out after noticing your corrections before your reply.

QUOTE
If you sample at 1hz (and your signal is limited to 0.5hz), you can record and reconstruct a signal with a peak at 5.23 seconds. If you used a low bitdepth, the peak may be shifted a bit (like 0.01s). If you used a high bitdepth, the position of the peak will be more precise. The point I was making was, you cannot have *infinite* precision. But you can get pretty close. cool.gif

My point was that you can only get closer than the samplerate, by sacrificing the accuracy of all the other samples in the record - and then you would need to a record of accuracy weighting per sample, to interprate the record as intended whistling.gif

QUOTE (Canar @ Oct 8 2006, 00:26) *
ChiGung, it is increasingly apparent you are not investing any effort in trying to understand what we are saying. I am not unused to this behaviour from you. I will try something concrete to show you what we are saying, then I advise that people stop posting here. This is a foolish response to trolling that is solved by a little bit of focused EE research on CG's part.

I see we are back to this are we. Forget it then.


--------------------
no conscience > no custom
Go to the top of the page
+Quote Post
Canar
post Oct 8 2006, 01:05
Post #38





Group: Super Moderator
Posts: 3358
Joined: 26-July 02
From: princegeorge.ca
Member No.: 2796



I've provided a mathematical example of why your position is in error and an analysis of your posting style. We are back to nothing. You seem to think your position is somehow without flaw, despite the elaborate and time-consuming explanations of many. I'm simply recommending that people realize that further discussion appears to be utterly futile. You have your position, and no amount of reasoning will change that.

Edit: on consideration, the values for the data set I've given may be in error. It still remains that for such a high-frequency value, there is a great number of values that would represent varying phase shifts for that signal.

This post has been edited by Canar: Oct 8 2006, 01:10


--------------------
You cannot ABX the rustling of jimmies.
No mouse? No problem.
Go to the top of the page
+Quote Post
cabbagerat
post Oct 8 2006, 08:07
Post #39





Group: Members
Posts: 1018
Joined: 27-September 03
From: Cape Town
Member No.: 9042



For your viewing pleasure, here's a quick demonstration that 16/44.1 PCM can resolve 10ns differences in time between two signals. The code is MATLAB, but if you don't have MATLAB, then download Octave (it's free) which will run this code without modification.
CODE
fs = 44100; %sample rate
ts = 1/fs; %sample period
bd = 16; %bit depth
f0 = 1e3; % frequency of wave
bd_scale = 2^(bd-1);
x=0:(1/fs):0.01;
y = round(cos(f0*2*pi*x)*bd_scale);
y2 = round(cos(f0*2*pi*(x+1e-8))*bd_scale);
plot(x, y1-y2, 'r');

Chigung's assertion that you sacrifice the accuracy of other samples is, in my mind, quite a stretch. Do you have a demonstration of this (in code, or in a theoretical treatment)?


--------------------
Simulate your radar: http://www.brooker.co.za/fers/
Go to the top of the page
+Quote Post
ChiGung
post Oct 8 2006, 15:02
Post #40





Group: Members
Posts: 439
Joined: 9-February 05
From: county down
Member No.: 19713



QUOTE (cabbagerat @ Oct 8 2006, 08:07) *
For your viewing pleasure, here's a quick demonstration that 16/44.1 PCM can resolve 10ns differences in time between two signals. The code is MATLAB, but if you don't have MATLAB, then download Octave (it's free) which will run this code without modification.
CODE
snip statement demonstrating the precise resolution of known variables

Chigung's assertion that you sacrifice the accuracy of other samples is, in my mind, quite a stretch. Do you have a demonstration of this (in code, or in a theoretical treatment)?

I am happy for this practical request.

Regarding:
QUOTE ("chigung")
The situation is, that the positioning of the brightness peak in the record is limited by the fact that the record has an implicit bandlimit. The position of the brightness peak in the source image is not implicity restricted by this limitation. (edit: yes the peak could be precisely positioned if we could employ all of the information stored in surrounding samples to do so - but all those other samples have information of their own to carry*) .

-------------------------------------------------------------------
Visualise a sequence of samples:

a,b,c,d,e,f,g,h,i,j

Suppose we are interested in the records solution between e and f. Perhaps we are looking for the precise location of the summit of a spike or perhaps the precise location when the recorded level achieves a value, like level=0. You must be able to propose a condition of the level to locate in time, in order for any statements about the records ability to locate detail in time to have meaning.

Propose a condition to locate then.
Then arrange any test values you like for all the levels.
Then locate your condition between e and f.

You will be able to do so, to the degree of precision noted frequently throughout this thread.

Then change the value of any single sample.
The location of your condition will change.
The location of the condition can be altered to occur anywhere between the bounding samples by altering the other samples in the record. (note ,depending on the condition sought, it may also be possible to make it not occur at all)

This is because the location of that condition is the result of a calculation which employs simultaneously all of the levels. The information which is used to store the conditions location, is that which is contained in all the samples. But that is an unnatural reading of the record (it is not being interprated just as normal PCM) We are effectly using a long 'read in' and 'read-out' period to achieve the accurate placement of the condition. We are treating the other samples as disposeable, when in normal PCM recording, each sample must have essentialy attributed the same importance as each other.

Its as though, we are trying to discover PCMs ability to precise locate details in time, so we test its ability to locate a single detail in time -arranging the whole record to do that locating. It is an unnormal reading of the record - an overreading of the relevance of the levels indicated conditions at the interval we are focusing on with an assumption of compliance of all the other levels.

To try to alter the indicated travel of the level to fit our intentions, is like trying to poke lumps out of a mattresse and finding when we do so, lumps appear in other parts of the mattresse. We can only arrange the shape we like in one bit of the mattrese by causing distortion in the rest. After doing so, if we could discard the rest of the mattress, then shape we had arranged would dissappear as it was the whole mattresse which informed the shape of the little part we were interested in.


--------------------
no conscience > no custom
Go to the top of the page
+Quote Post
Canar
post Oct 8 2006, 15:28
Post #41





Group: Super Moderator
Posts: 3358
Joined: 26-July 02
From: princegeorge.ca
Member No.: 2796



So because sinc() interpolation is weird, PCM fails... rolleyes.gif

This post has been edited by Canar: Oct 8 2006, 15:32


--------------------
You cannot ABX the rustling of jimmies.
No mouse? No problem.
Go to the top of the page
+Quote Post
cabbagerat
post Oct 8 2006, 15:51
Post #42





Group: Members
Posts: 1018
Joined: 27-September 03
From: Cape Town
Member No.: 9042



QUOTE (ChiGung @ Oct 8 2006, 06:02) *
This is because the location of that condition is the result of a calculation which employs simultaneously all of the levels. The information which is used to store the conditions location, is that which is contained in all the samples. But that is an unnatural reading of the record (it is not being interprated just as normal PCM) We are effectly using a long 'read in' and 'read-out' period to achieve the accurate placement of the condition. We are treating the other samples as disposeable, when in normal PCM recording, each sample must have essentialy attributed the same importance as each other.
I can't really follow your argument. Are you saying that it's impossible to reconstruct a properly sampled signal from a set of arbitrarily accurate samples using only causal filters? If so, that's quite profound and almost certainly wrong, but if you have evidence that this is true, the IEEE transactions on signals and systems is the right place for it, not HA.

If you are saying that, in PCM, distortion is introduced by the impulse response of the system, then please demonstrate that this distortion is even plausibly audible.

QUOTE
So because sinc() is weird, PCM fails... rolleyes.gif
smile.gif

This post has been edited by cabbagerat: Oct 8 2006, 15:52


--------------------
Simulate your radar: http://www.brooker.co.za/fers/
Go to the top of the page
+Quote Post
ChiGung
post Oct 8 2006, 16:10
Post #43





Group: Members
Posts: 439
Joined: 9-February 05
From: county down
Member No.: 19713



QUOTE (cabbagerat @ Oct 8 2006, 15:51) *
I can't really follow your argument. Are you saying that it's impossible to reconstruct a properly sampled signal from a set of arbitrarily accurate samples using only causal filters?

Nope. The demonstration was quite clear and explainations have been labouriously reworded for the comprehension of whoever seeks it.


--------------------
no conscience > no custom
Go to the top of the page
+Quote Post
KikeG
post Oct 8 2006, 17:59
Post #44


WinABX developer


Group: Developer
Posts: 1578
Joined: 1-October 01
Member No.: 137



As others have said, time resolution of PCM is the inverse of sampling rate multiplied by nš of discrete levels. In other words,

T = 1/(fs*2^n)

Where n is nš of bits. And that's all.
Go to the top of the page
+Quote Post
ChiGung
post Oct 8 2006, 18:14
Post #45





Group: Members
Posts: 439
Joined: 9-February 05
From: county down
Member No.: 19713



QUOTE (KikeG @ Oct 8 2006, 17:59) *
As others have said, time resolution of PCM is the inverse of sampling rate multiplied by nš of discrete levels. In other words,

T = 1/(fs*2^n)

Where n is nš of bits. And that's all.

So your, considered 'contemporary' definition of 'time resolution' of PCM becomes finer as the number of included levels increases. And you appreciate no further clarification of what your definition practicaly means for the resolution of details throughout time in the record. Fine, but the scope of this topic provided for a wider discussion.


--------------------
no conscience > no custom
Go to the top of the page
+Quote Post
KikeG
post Oct 8 2006, 18:24
Post #46


WinABX developer


Group: Developer
Posts: 1578
Joined: 1-October 01
Member No.: 137



QUOTE (ChiGung @ Oct 8 2006, 18:14) *
So your, considered 'contemporary' definition of 'time resolution' of PCM becomes finer as the number of included levels increases.

Yes. Resolution is limited by sampling rate and dynamic range or SNR or quantization noise, call it as you prefer.
QUOTE
And you appreciate no further clarification of what your definition practicaly means for the resolution of details throughout time in the record. Fine, but the scope of this topic provided for a wider discussion.

Resolution refers about the smallest time event that can be resolved. Why make it more complicated?

This post has been edited by KikeG: Oct 8 2006, 18:26
Go to the top of the page
+Quote Post
ChiGung
post Oct 8 2006, 18:55
Post #47





Group: Members
Posts: 439
Joined: 9-February 05
From: county down
Member No.: 19713



QUOTE (KikeG @ Oct 8 2006, 18:24) *
Resolution refers about the smallest time event that can be resolved. Why make it more complicated?

Nice question cool.gif I may try to reiterate but to save my effort let me first requote some explaination already provided which may have been missed:
QUOTE ("Chigung")
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'.


There is a difference between the 'time resolution' commonly presented, and the ability to record in PCM the temporal location of events accurately. Basically this common use of the term 'time resolution' is (apparently) widely misunderstood. Detail of any time localisable events, will be distorted by the implicit lowpass of conversion by an unknowable amount (post conversion) by upto a sample-period-width of difference. The common demonstration to prove the ability to record the location of events to finer than a sample width accuracy, depends on the precise aggreance (exclusive employment) of many samples to place just one test detail within a whole run of samples - it is a very unfair demonstration and actualy demonstrates my point -that to achieve subsample positioning of a single detail requires the use of more than one sample. In a normal PCM record, the altering of other sample points to maintain subsample positioning of details in the origional waveform, cannot be done, all details are susceptable to be shifted by unrecoverable amounts up to the new sample interval (and of course some details may be lost altogether) Downsampling, involves introducing uncertainty of the waveforms precise form (as information is discarded)
So the practical 'time resolution' of PCM, as in 'how accurately can the temporal placement of events in the origional waveform which survive conversion be known, is (sublimely) to within the limits of the sample period - because we do not have the lost high frequency information of any events anymore.

This post has been edited by ChiGung: Oct 8 2006, 18:57


--------------------
no conscience > no custom
Go to the top of the page
+Quote Post
Woodinville
post Oct 8 2006, 19:37
Post #48





Group: Members
Posts: 1402
Joined: 9-January 05
From: JJ's office.
Member No.: 18957



QUOTE (ChiGung @ Oct 8 2006, 10:14) *
So your, considered 'contemporary' definition of 'time resolution' of PCM becomes finer as the number of included levels increases. And you appreciate no further clarification of what your definition practicaly means for the resolution of details throughout time in the record. Fine, but the scope of this topic provided for a wider discussion.



Your words here are meaningless. "Appreciate no further clarification" is meaningless, at least without your providing some clear, testable, verifiable "clarification" that you believe necessary.

With the understanding stated above, the issue is settled. You have your answer, and you might as well live with it. I don't see any reason to engage you further until you use language that those skilled in the art can actually recognize as having technical meaning.

QUOTE (ChiGung @ Oct 8 2006, 10:55) *
Detail of any time localisable events, will be distorted by the implicit lowpass of conversion by an unknowable amount (post conversion) by upto a sample-period-width of difference.



This is completely incorrect. Please do not state it as a fact, and please do not reproduce this myth where it may confuse others.

You clearly have no understanding of the function and effect of the antialiasing filter at the input to the sampling process, or of the meaning of a bandwidth limited signal.

Try this: Create a gaussian pulse. Since you are making expert judgements here, you should have no trouble doing that.

Create a gaussian pulse that is down 90dB at 22.05 kHz. Surely that will be easy, since it involves the simplest Fourier Identity in existance.

Now, figure out the sample values for that. Shift the time by 1/10000th of a sample time, and figure out the sample values. They are different.

Q.E.D.


--------------------
-----
J. D. (jj) Johnston
Go to the top of the page
+Quote Post
ChiGung
post Oct 8 2006, 19:57
Post #49





Group: Members
Posts: 439
Joined: 9-February 05
From: county down
Member No.: 19713



QUOTE (Woodinville @ Oct 8 2006, 19:37) *
Your words here are meaningless. "Appreciate no further clarification" is meaningless, at least without your providing some clear, testable, verifiable "clarification" that you believe necessary.

You dont like my online persona, and I sure dont like yours woody lets leave it a that.

Others regard the level of attention I am up against here.

Clear, testable, verifiable clarifications have been provided for those sincerely intereseted in them.

QUOTE
QUOTE (ChiGung @ Oct 8 2006, 10:55) *
Detail of any time localisable events, will be distorted by the implicit lowpass of conversion by an unknowable amount (post conversion) by upto a sample-period-width of difference.

This is completely incorrect. Please do not state it as a fact, and please do not reproduce this myth where it may confuse others.

It is fact - there will be people using this forum with the understanding and experience to realise it.
Perhaps in your haste to offend me, you forgot the type of conversion being discussed is neccessarily a downsample (ie. a type involving an implicit lowpass)

QUOTE
Try this: Create a gaussian pulse. Since you are making expert judgements here, you should have no trouble doing that.
Create a gaussian pulse that is down 90dB at 22.05 kHz. Surely that will be easy, since it involves the simplest Fourier Identity in existance.
Now, figure out the sample values for that. Shift the time by 1/10000th of a sample time, and figure out the sample values. They are different.

Yeah you did forget that. There is no downsample involved there, just a shifting of a record.
Pay the thread better attention before posting please.

QUOTE ("chigung")
Depending on the characteristics of the information conveyable from the origional media (lenses, microphones, physics of air etc) it may be suitably restricted for precise capture/repoduction by certain samplerates, but because the source media may also not be suitably restricted (and very often is not) we have to allow for this possibility. It's surprised me that there has been a strong tendency to discount this as recognising source media may have finer resolution than target samplerates is fundamental to sensible statements of how accurately target samplerates can record the information of various sources.


This post has been edited by ChiGung: Oct 8 2006, 19:59


--------------------
no conscience > no custom
Go to the top of the page
+Quote Post
Canar
post Oct 8 2006, 20:08
Post #50





Group: Super Moderator
Posts: 3358
Joined: 26-July 02
From: princegeorge.ca
Member No.: 2796



ChiGung, despite your frequent reassertions to the contrary, we are still not following you. Your explanations have not been clear, precise, testable, or verifiable.

So, there are two possibilities: you are misunderstanding and are incorrect, or all the technically competent members who are assuring you and providing mathematical proof of the inaccuracy of your position are misunderstanding you and are providing evidence that is not related to the topic at hand. I would suggest you consider the possibility of the former, as we consider the possibility of the latter and try and understand exactly what you're trying to convey here.

This post has been edited by Canar: Oct 8 2006, 20:12


--------------------
You cannot ABX the rustling of jimmies.
No mouse? No problem.
Go to the top of the page
+Quote Post

7 Pages V  < 1 2 3 4 > » 
Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 31st August 2014 - 06:01