Jerry Avins <jya@ieee.org> wrote in news:Yfcxm.82943$u76.42090@newsfe10.iad:> Jimmy J wrote: >> Eric Jacobsen <eric.jacobsen@ieee.org> wrote in >> news:y7Wwm.241160$0e4.137127@newsfe19.iad: >> >>> On 9/30/2009 6:00 PM, Jimmy J wrote: >>>> Rune Allnor<allnor@tele.ntnu.no> wrote in >>>> news:52a97f4b-2bec-4b6b-a6da-d8303fc3f7e1@37g2000yqm.googlegroups.co >>>> m: >>>> >>>>> On 1 Okt, 00:27, "macsdev"<macs...@gmail.com> wrote: >>>>>> Hi, >>>>>> >>>>>> I have a doubt in Sampling of Signals from a Theoretical Point of >>>>>> View. When we sample a signal, are we losing anything in terms of >>>>>> Energy of the signal? Intuitively, it seems so. But I also know >>>>>> that there is no loss of Information (since the spectrum is still >>>>>> intact, if we sample at a proper rate). Is my reasoning correct >>>>>> or is it flawed somewhere? >>>>> Flamebait? OK, here we go: >>>>> >>>>> Once the signal has been sampled, you only have a sequence of >>>>> numbers, not a physical quantity. Since no physical quantities >>>>> are involved, the term 'energy' has no relevance. >>>>> >>>>> Rune >>>> >>>> I doubt that the OP really means what he says, but that's a >>>> separate issue. The fact of the matter is that unless you want to >>>> redefine the classical concept and definition of energy spectral >>>> density, your reply is nothing other than pure unadulterated bull >>>> shit. By definition, if you have an energy density spectrum and >>>> integrate it, you get total signal energy. >>> He didn't say he had an energy density spectrum (whatever that is), >>> so I wouldn't assume he can integrate anything to get energy. >>> >>> More to the point, concepts like power and energy are only >>> meaningful to discrete sequences for which those values may be >>> relevant. A sequence of numbers representing total daily rainfall >>> over a number of days is unlikely to provide information in terms of >>> Joules or Watts. A sequence of numbers representing a voltage >>> measured over known time periods on a fixed impedance may, however. >>> >>> I think what Rune was saying was that the sequence of numbers has no >>> energy itself, which is true, and I'm pointing out that IF the units >>> of the measured samples lend themselves to computing energy for the >>> signal sampled then that can certainly be done. >>> >>> One always has to be careful to properly interpret the results of >>> any process. Computing the "Power Spectral Density" of the sequence >>> representing the gas volume of successive tokes on the bong won't >>> yield Watts/Hz. >> >> >> For whatever reason, you seem to have either missed or intentionally >> ignored the first half dozen or so words of the OP which were "I have >> a doubt in Sampling of Signals." Energy spectral density and power >> spectral density are defined specifically with reference to the >> analysis of "signals." The issue of whether or not the OP has >> available an energy density spectrum is irrelevant. My comment >> pertained to Rune Allnor's idiotic and false statement "Since no >> physical quantities are involved, the term 'energy' has no >> relevance." Whether you and Rhune Allnor are willing to admit it or >> not, signal energy is a physical quantity, by definition. > > You have asserted in the past that you know little or nothing about > DSP. Here, you removed all doubt. > > JerryThis is not a DSP issue, and all your idiotic comment does is to shine a bright light on either your gross ignorance or your intellectual dishonesty, and to illustrate what a jackass you really are.
Doubts in Sampling
Started by ●September 30, 2009
Reply by ●October 1, 20092009-10-01
Reply by ●October 1, 20092009-10-01
>Hi, > >I have a doubt in Sampling of Signals from a Theoretical Point of View. >When we sample a signal, are we losing anything in terms of Energy ofthe>signal? Intuitively, it seems so. But I also know that there is no lossof>Information (since the spectrum is still intact, if we sample at aproper>rate). Is my reasoning correct or is it flawed somewhere?If you restore a properly sampled signal to the analogue domain, with proper band limiting of the resulting analogue signal, you can get very close to the original signal. The residual mismatch is a combination of: - Limited resolution in any real world sampling - Imperfect filtering in any filter, theoretical or real world - Noise (nothing is impossible - there's always kTB :-) ) Intuitively it would appear that nothing is lost, beyond the real world limitations of any practical system, and the inevitable wide band noise. Steve
Reply by ●October 2, 20092009-10-02
>Hi, > >I have a doubt in Sampling of Signals from a Theoretical Point of View. >When we sample a signal, are we losing anything in terms of Energy ofthe>signal? Intuitively, it seems so. But I also know that there is no lossof>Information (since the spectrum is still intact, if we sample at aproper>rate). Is my reasoning correct or is it flawed somewhere? > > >An ideal band-limited signal, which has infinite duration, has infinite energy. When we sample such a signal, yes, we lose energy, but it is still infinite. If you sample at a proper rate, which is more than the Nyquist's rate, what remains the same is the average power of the signal. The average power of such a continuous time signal and its properly sampled discrete-time signal is the same. But a real world signal, which is time-limited and hence, not band-limited, has finite energy and sampling of the signal leads to loss of some of the energy. This loss is manufactured in aliasing. Nikhil P.S.: Folks, please correct me if I am wrong.
Reply by ●October 2, 20092009-10-02
On 01-10-2009 at 01:32:50 Rune Allnor <allnor@tele.ntnu.no> wrote: (...)> Once the signal has been sampled, you only have a sequence of > numbers, not a physical quantity. Since no physical quantities > are involved, the term 'energy' has no relevance.(...) I support this. There is no energy in samples (numbers). They are just information. Sampled signal is an idea of real signal. -- Mikolaj
Reply by ●October 2, 20092009-10-02
>On 01-10-2009 at 01:32:50 Rune Allnor <allnor@tele.ntnu.no> wrote: > >(...) >> Once the signal has been sampled, you only have a sequence of >> numbers, not a physical quantity. Since no physical quantities >> are involved, the term 'energy' has no relevance. >(...) > > >I support this. >There is no energy in samples (numbers). >They are just information. >Sampled signal is an idea of real signal. > > >-- >Mikolaj >I disagree. I want to distinguish between the sampled signal and the sequence of numbers. A sampled signal is still a physical quantity. A sequence of numbers is a representation of the sampled signal, like a snapshot taken and is stored in some memory. Now to re-create the sampled signal (say, a voltage signal) from the sequence of numbers stored in the memory requires electrical energy. It is like this.... we represent sinusoidal signal as sin (wt). To generate sin (wt), we need a function generator, which consumes energy. Likewise, a sampled signal is represented as... for example, [1.2, 2.7, 5.6, 4.1]. To generate a physical signal from this needs energy. Nikhil
Reply by ●October 2, 20092009-10-02
On 2 Okt, 13:13, "Nikhil A D" <nikhil2...@gmail.com> wrote:> >On 01-10-2009 at 01:32:50 Rune Allnor <all...@tele.ntnu.no> wrote: > > >(...) > >> Once the signal has been sampled, you only have a sequence of > >> numbers, not a physical quantity. Since no physical quantities > >> are involved, the term 'energy' has no relevance. > >(...) > > >I support this. > >There is no energy in samples (numbers). > >They are just information. > >Sampled signal is an idea of real signal. > > >-- > >Mikolaj > > I disagree. I want to distinguish between the sampled signal and the > sequence of numbers.*Almost* correct, but you didn't define what a 'sampled signal' is. Thetrem can be interpreted as either "a physical quantity that has been fed to the input of an ADC" or "the sequence of numbers emerging at the output of an ADC." You need to be acutely aware of the two meanings, and the possible mix-up. I'll rephrase to avoid the term: You have to distinguish between 1) the physical quantity that was sampled 2) the sequence of numbers made up by the samples.> A sampled signal is still a physical quantity.Of course the physical quantity that was sampled is a physical quantity. To the extent it still exists after samplig took place. Again, your term 'sampled signal' has not been defined.> A > sequence of numbers is a representation of the sampled signal,The discrete representation of the physical quantity that was sampled is a sequence of numbers.> like a > snapshot taken and is stored in some memory. Now to re-create the sampled > signal (say, a voltage signal) from the sequence of numbers stored in the > memory requires electrical energy.Yes, but one does not necessarily need to recreate a physical signal from the samples. As long the data remain in digital domain, they are no more than a sequence of numbers. Rune
Reply by ●October 2, 20092009-10-02
Nikhil A D wrote:>> On 01-10-2009 at 01:32:50 Rune Allnor <allnor@tele.ntnu.no> wrote: >> >> (...) >>> Once the signal has been sampled, you only have a sequence of >>> numbers, not a physical quantity. Since no physical quantities >>> are involved, the term 'energy' has no relevance. >> (...) >> >> >> I support this. >> There is no energy in samples (numbers). >> They are just information. >> Sampled signal is an idea of real signal. >> >> >> -- >> Mikolaj >> > > I disagree. I want to distinguish between the sampled signal and the > sequence of numbers. A sampled signal is still a physical quantity. A > sequence of numbers is a representation of the sampled signal, like a > snapshot taken and is stored in some memory. Now to re-create the sampled > signal (say, a voltage signal) from the sequence of numbers stored in the > memory requires electrical energy. > > It is like this.... we represent sinusoidal signal as sin (wt). To > generate sin (wt), we need a function generator, which consumes energy. > Likewise, a sampled signal is represented as... for example, [1.2, 2.7, > 5.6, 4.1]. To generate a physical signal from this needs energy.Does the energy required to run the function generator equal the energy of the signal being reproduced? If not, how are they related? We're back to "Nothing is better than a piece of bread." Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●October 2, 20092009-10-02
On Fri, 2 Oct 2009 04:55:09 -0700 (PDT), Rune Allnor <allnor@tele.ntnu.no> wrote:>Yes, but one does not necessarily need to recreate a physical >signal from the samples. As long the data remain in digital >domain, they are no more than a sequence of numbers.True but to distinguish one set of numbers from another set, say to make the judgment "seqeunce A has more power than sequence B" one doesn't have to feed them to a DAC/scope. You can look at the sequences and tell if you were to feed them to such a system they're different and make qualitative judgments about them so the sequences are not meaningless bunch of numbers. Under the right conditions they do represent the original signals they were derived from -- Muzaffer Kal DSPIA INC. ASIC/FPGA Design Services http://www.dspia.com
Reply by ●October 2, 20092009-10-02
Muzaffer Kal wrote:> On Fri, 2 Oct 2009 04:55:09 -0700 (PDT), Rune Allnor > <allnor@tele.ntnu.no> wrote: >> Yes, but one does not necessarily need to recreate a physical >> signal from the samples. As long the data remain in digital >> domain, they are no more than a sequence of numbers. > > True but to distinguish one set of numbers from another set, say to > make the judgment "seqeunce A has more power than sequence B" one > doesn't have to feed them to a DAC/scope. You can look at the > sequences and tell if you were to feed them to such a system they're > different and make qualitative judgments about them so the sequences > are not meaningless bunch of numbers. Under the right conditions they > do represent the original signals they were derived fromIs the power your brain uses to judge the signal related to the power it represents? If it does, more power to you! Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●October 2, 20092009-10-02
On Fri, 02 Oct 2009 13:08:54 -0400, Jerry Avins <jya@ieee.org> wrote:>Muzaffer Kal wrote: >> On Fri, 2 Oct 2009 04:55:09 -0700 (PDT), Rune Allnor >> <allnor@tele.ntnu.no> wrote: >>> Yes, but one does not necessarily need to recreate a physical >>> signal from the samples. As long the data remain in digital >>> domain, they are no more than a sequence of numbers. >> >> True but to distinguish one set of numbers from another set, say to >> make the judgment "seqeunce A has more power than sequence B" one >> doesn't have to feed them to a DAC/scope. You can look at the >> sequences and tell if you were to feed them to such a system they're >> different and make qualitative judgments about them so the sequences >> are not meaningless bunch of numbers. Under the right conditions they >> do represent the original signals they were derived from > >Is the power your brain uses to judge the signal related to the power it >represents?I am not sure how my brain works (or how well) so I can't answer that question but what I can tell you something I know a little about. In digital logic (say a DSP datapath) input signals with low variance usually generate fewer transitions in the circuit so they have usually cause lower power consumption to be processed (I added the two usuallys because your circuit could be bound by very high leakage and the marginal power difference because of the transistions maybe too small to be observed or you may have a circuit which generates internal transitions not related to its input, say to deter power signature analysis). So it's really not true to say a sequence of numbers are indistinguishable from others and/or they're meaningless as long as they're numbers. Another example is an adaptive FIR, say implementing an echo canceller. When converged, the filter definitely knows what type of a channel you are using and depending on how long the echo tail is or how many taps there are on the wire causing echo, the FIR filter consumes more or less power trying to cancel the echo. There are more non-zero taps to be multiplied with and non-zero results to be added. So the sequence of numbers definitely do have a consequence on the power a digital circuit consumes to process it. -- Muzaffer Kal DSPIA INC. ASIC/FPGA Design Services http://www.dspia.com
