Quote from: ChiGung on 18 November, 2006, 04:49:54 PMIm very interested to hear about other & better methods..............Then how come you won't accept them when they are offered?
Im very interested to hear about other & better methods..............
Try it. Learn.
I have a suggestion, go load Cygwin, Xserver, and Octave.
It will save you lots of time and eventually you'll understand that phase shift and time delay are the same thing,
maybe if you didnt save time, and built your own codebase, you just might realise that "phase shift and time delay" are different....
Phase shift's 'dimension' is tightly cyclic,
Phase shift's 'dimension' is tightly cyclic, time's dimension is not normaly considered so, most commonly an infinite line. The geometry of phase differs from the geometry of time, phase has a finite distribution through its own 'time' (loop) and an infinite distribution throughout 'real' time. This makes phase detail imperfect for locating finite positions in 'real' time. If I could recall Euclid as well as others i could say it better -but basicaly time delay and phase shift are different.
btw, i confirmed that the spike in the preceeding plots is a bug, throwing much uncertainty on the programs performance at the moment, but ill get it fixed (the toil is in the assembling)
Euclid? If you want to have a scientific discussion perhaps following the standard of scientific publications would be a good idea. Either put up a proof or a reference to a published document containing a proof.
It looks like we're going in circles.
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.
Resolution refers about the smallest time event that can be resolved.
Chigung wrote: "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.
So, we have two filters. If _both_ filters block everything above fs/2, then the sampling stage itself will be transparent - lossless, if you like. In other words, these two systems would be identical...
ChiGung:"btw, i confirmed that the spike in the preceeding plots is a bug, ....maybe if you didnt save time, and built your own codebase, you just might realise that "phase shift and time delay" are different...."One wonders how you can make these two statements and keep a straight face.
chigung: "maybe if you didnt save time, and built your own codebase, you just might realise that "phase shift and time delay" are different...."I see you're resorting to insuts again.
chigung:Phase shift's 'dimension' is tightly cyclic,No, it's not. 2 pi is not the same phase shift as 4 pi, although sometimes measuring which is which requires good understanding, or in some cases even the use of time delay to disambiguate between 2 pi and 4 pi.
Woodinville:"I would suggest, again, that you go back and learn the basic definitions for what you seek."- I gather if i suggested that to you, you would report insult.
Untrue. I limit my research to protect my originality. Education is to Innovation what Masterbation is to Procreation. I have learned adequate tools at home, school and university and beyond to suit my own designs.
As you said, a phase shift on its own doesn't really have any meaning.
- hence why the fourier transform returns both magnitude and phase plots.
Maybe you could give an example where this information would be relevant?
techie: "captain we have located a 'spike' event on the PCM sensor"captain:"what is the position of the spikes peak teki?"techie:"324.37643 sampling intervals exactly captain"captain:"how can you be so precise?"techie:"because time delays are quite precisely encodable in PCM"But a natural spike, will have an unknown frequency spectrum, the tools (information) to locate the true peak with certainty had to be removed before the downsample, so we can make the best guess by assuming the 'subsample deviators' (frequencies beyond nyquist) were all flat anyway but thats just a guess, the true peak could have been anywhere in the sample interval. If it was actualy somewhere other than the record suggests most likely, that information was contained in the lowpassed higher frequencies which now manifest as the unrecorded gaps between samples.
Imagine it was an examine question: what applications of pcm records do you think are susceptable to timing uncertainties caused by samplerate enforced bandlimitation ? How does the concept and common usage of the term 'time resolution' contrast with practicaly introduced distortions?
I agree a reference point is needed, a phase shift at a specified frequency does not specify an exact time, as does a time delay not specify an exact time - but both a phase shift at a specified frequency and a time delay are equivalent in these terms,
and it's possible to have a phase shift of greater than 2*pi allowing any duration to be specified.
Perhaps looking at it from a different angle is needed, I think in the end we're interested in if PCM can follow its analogue band-limited source counterpart exactly. Quantization will add a noise error signal so 'exact' won't be fully achievable. At the moment, the movement of peaks haven't be attributed to anything other than removal of frequencies. Just a thought.
These questions are only valid to the extent that they question the use of ANY form of sampling, not only PCM.
Again, all the ideal theoretical mathematical explainations of sampling I've read don't indicate any such timing uncertainties - only problems caused by causality and the knowledge of all samples and the like. Practically I've not tested this but again, in the physical world things are a bit different!
I think we are deviating from the point, but totally disagree with the phase shift requiring a mapping onto an exact period in time,
In terms of your exact study, of how low pass filtering affects timing, what kind of lowpass filter are you studying? I'd be interested in this filters transfer function. Is this filter being applied in the digital domain or analogue before sampling?
I don't disagree with anyone who performs any study or investigation, as I find it helps to perform these things to allow a clear view of why things work.
Quote...You didn't have to "prove" that bandlimitation changes something. Nobody questioned it."Ive had to respond to a great deal of dismissals and missreports, but here are some quotes about youre claim that "nobody questioned it":cabbagerat> 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.Note the sly attempt to shift context from detectability to "audibility"
...You didn't have to "prove" that bandlimitation changes something. Nobody questioned it."
QuoteResolution refers about the smallest time event that can be resolved.KikeG never questioned its existence, just dismissed its relevance. I am attempting resolve events and observe their timing differences throughout different bandwidths/samplerates, to inform claims about pcm time resolution.
QuoteChigung wrote: "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.(not just "incorrect" but completely incorrect - followed by an order to desist saying so(!)
...Who cares? The thread is "what is time resolution", this is the R&D section of an audio forum. But hey it might be true,that no one but me really cares about the subject.
cabbagerat> "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."chigung: Note the sly attempt to shift context from detectability to "audibility"Actually band limitation is generally not considered distortion (as in "non-linear" distortions). You both were just talking about different kinds of distortion.
chigung:"KikeG never questioned its existence, just dismissed its relevance. I am attempting resolve events and observe their timing differences throughout different bandwidths/samplerates, to inform claims about pcm time resolution."Then what are "timing events"? This discussion seems pointless because we don't seem to have a common ground concerning many (pseudo-) technical terms. Everybody knows what a peak is. <rethorical>But what is "timing event"?</rethorical>
That's probably because Woodinville interprets "timing event" differently. This only shows the need for a common vocabulary with precisly defined terms.
"Any time localisable event" is pretty much anything and also includes the "events" whose location won't be altered during bandlimiting.
One could also think of "time event" as a specific energy distribution in time (Woodinville's example: gaussian pulse). This (or the lower spectrum part that's left after lowpassing/sampling) can be located perfectly if the signal has been properly sampled. The only thing that'll mess things up here is noise (eg quantization noise).
It's you not me nor 2B nor Woodinville that connects peaks and their possible movement to "time resolution" -- a term whose notion we havn't agreed upon.
After all the "who cares"/"so what"-talk I was kind of expecting you to mention a case where a possible movement of peaks poses an actual problem. I still can not understand your obsession about those things on arbitrary signals ("arbitrary" = those that may show different locations of those points you look for after bandlimiting).
"Detail of any time localisable(sic) events, will be distorted by the implicit lowpass of conversion by an unknowable amount (post conversion) by upto(sic) a sample-period-width of difference."-Is very explicit english. "time localisable(sic) events" are> [events] [which are possible to locate in] [time].
The type of distortion i was talking about, was already described
Regarding 'timeable events' I use such terms as a broad set of which 'peaks' are a member.I simply wished to refer to any kind of detail which might be identified and pinpointed in time within waveforms. Basicaly anything you might think of which might be precisely locateable in time (in a prcm record) -( which peak of level is an example of).
I think you eventualy will understand how the movement of measureable occurences in time which might result from lowpassing, informs 'time resolution' @ pcm samplerates.
My obsession here, has simply been to defend my reputed understanding of the topic.
Im not your student.
QuoteYou're doing nobody any good by failing to read up on the field you're talking about before you work.Untrue. I limit my research to protect my originality. Education is to Innovation what Masterbation is to Procreation
You're doing nobody any good by failing to read up on the field you're talking about before you work.
The time and frequency domains are mathematically identical, but are very different to conceptualize. If you wish to discover the ways in which a frequency domain transform affects audio, you must look at it from a frequency domain perspective if you wish to understand well. What you are doing is looking at a frequency domain transformation from a time domain perspective, and are getting complex results that you don't really understand. Because you don't understand them, you assume there's something weird happening there. There isn't. You're just not looking at it correctly.
In the meantime i expect honest estimates to be made here of the temporal resolution of pcm records. Because the proof will follow
Quote from: 2Bdecided on 17 November, 2006, 07:25:20 AMAll you have shown is that frequency components in signal A contributed to the position of peak A, and these have been removed, thus moving the peak. However, there is no limit to where peaks can occur. It is not like the quantisation amplitude resolution limit at all! It is not a time resolution limit, just a predictable effect of low pass filtering a signal.If there is no limit to where the peaks can occur, how come they cant be arranged to occur in the correct place between records of differing sample rates? Why must they be susceptible to unknown distortions during downsamples with your "no limitations" argument? Because their precise subsample positions are limited - by every other sample in the record which they are a part of. Thats why you cant normally use the "unlimited" resolution which you can infer - without distorting all other samples to create the subsample details. (done to provide some limited demonstrations in this thread, but not possible in practice where all samples must be treated equally)
All you have shown is that frequency components in signal A contributed to the position of peak A, and these have been removed, thus moving the peak. However, there is no limit to where peaks can occur. It is not like the quantisation amplitude resolution limit at all! It is not a time resolution limit, just a predictable effect of low pass filtering a signal.
I still don't get the obsession or difficulty. If a peak moves when low pass filtering, it's because you are deleting the part of the signal that put the peak there - how could it not move? It's not a limit in resolution because, if the peak was supposed to be there ("there" being absolutely anywhere), it could and would be.
Nothing fake, clever or contrived. PCM audio allows a peak to exist absolutely anywhere - on samples, and anywhere between samples. What it doesn't allow is audio above fs/2. It's a frequency domain phenomena, not a time domain phenomena.
Put another way, there have been great objections put forward to my report that unless we have secure knowledge of the frequency distribution of the source, time resolution is practicaly around 1/2 the sample interval.What is "level resolution" then? Doesn't a pcm record of 8bit words differ in 'level resolution' from one of 16bit words? Or do you all contend that to a properly educated engineer, both records resolution of level are effectively infinite as well?
So you didn't even bother to read, never mind understand, that part where I contrasted quantisation (which does limit amplitude resolution) to sampling (which does not limit time resolution)?Or comment on the part where I ask just how stupid it would be to perform time domain analysis on the output of a graphic equaliser?
Let me draw a parallel. Try performing a time domain analysis on a nice linear-phase graphic equaliser with the bass at +6dB and the treble at -6dB. Would it change the time domain signal? Of course! It must change the time domain - you can't change one domain without affecting the other!But what we have is very much a frequency domain phenomena, any anyone who tries to analyse solely in the time domain is going to look very stupid - especially if they say they're going to do it for a random set of audio signals. Think about it - what on earth would it tell you?
I would have loved to hear from you about application examples where this does matter.