On Mon, 20 Aug 2007 05:46:19 -0800, floyd@apaflo.com (Floyd L. Davidson) wrote:>nospam@nospam.com (Don Pearce) wrote: >>On Mon, 20 Aug 2007 04:57:03 -0800, floyd@apaflo.com (Floyd L. >>Davidson) wrote: >> >>>Jerry Avins <jya@ieee.org> wrote: >>>>I like your categories. It is possible in concept to >>>>have a signal that is quantized in magnitude and >>>>continuous in time, but (unless we resort to counting >>>>electrons) I don't think it's possible in practice. >>> >>>If you quantize the magnitude, it is digital. That is >>>by definition. >> >>No it isn't. It isn't digital until you assign numerical values to >>those quantized levels. Until then it is simply a quantized analogue >>signal. > >If you quantize it, you *have* assigned a value to it, >and that value is not from a continuous set, but from a >discrete finite set, and therefore it is digital. > >A "quantized analogue signal" is digital by definition. >No, you haven't. You merely have a signal at a set of discrete levels. You need an analogue to digital converter to take each of those quantized levels and convert it into a digital word (of 1s and 0s). Digital means "represented by digits", not "in discrete voltage steps". d -- Pearce Consulting http://www.pearce.uk.com
Questions about equivalents of audio/video and digital/analog.
Started by ●August 19, 2007
Reply by ●August 20, 20072007-08-20
Reply by ●August 20, 20072007-08-20
On Aug 19, 4:01 pm, Radium <gluceg...@gmail.com> wrote:> > Is it true that unlike the-frequency-of-audio, the-frequency-of-video > has two components -- temporal and spatial? >Kind of. This gets into some pretty involved engineering and math and was originally used to get into how to analyze images when designers were first trying to develop television systems. It involves what is known as linear systems analysis, which originally was for one dimensional signals such as audio. In this type of analysis any arbitrary shape/waveform can be broken down into a collection of many sine waves of different frequency. For images this was extended to work as a two-dimensional array, with duplication of the signal by considering two sets of so-called "spatial frequencies", at right angles to each other. This was extended beyond TV engineering when optical engineers developed the Modulation Transfer Function by borrowing EE ideas of linear systems to predict and measure performance of optical systems. It involves things like Fourier transforms.> AFAIK, the-frequency-of-audio only has a temporal component. Do I > guess right?Right> > II. Digital vs. Analog > > Sample-rate is a digital entity. In a digital audio device, the sample- > rate must be at least 2x the highest intended frequency of the digital > audio signal. What is the analog-equivalent of sample-rate? In an > analog audio device, does this equivalent need to be at least 2x the > highest intended frequency of the analog audio signal? If not, then > what is the minimum frequency that the analog-equivalent-of-sample- > rate must be in relation to the analog audio signal? >The analog equivalent is, loosely, the bandpass or cutoff frequency of an analog filtering circuit. Any electrical network designed to reproduce faithfully the analog signal must have a bandpass such that the high frequency cutoff is equal to or higher than the highest frequency in the analog signal.> III. My Requests:
Reply by ●August 20, 20072007-08-20
Radium wrote:> On Aug 19, 2:50 pm, rfisc...@sonic.net (Ray Fischer) wrote: > >> Radium <gluceg...@gmail.com> wrote: > >>> Hi: > >>> I. Audio vs. Video > >>> Digitized (mono) audio has a single sample per each sampling >>> interval. >Well, yes and no. That's true for what is called PCM, used on the Compact Disc and MPEG. It is sort of true for Delta-Sigma coding, but the for the actual useful sampling rate limit, its not really true. D-S modulation is used for the Super Audio CD.> > There is no analog-equivalent of sample-rate? Then what the limits the > highest frequency an analog audio device can encode?The circuits used. All circuits have a low-pass filtering action of some sort. For example, 78 RPM records went up to maybe 10-12 kHz usefully, while 33s actually could go up to 40 kHZ if pushed (e.g. discrete quad.) Many high quality audio power amps will happily go to 100 kHZ or even a megahertz. This may be intrinsic with the circuits, or, far more common, a simple resistor-capacitor filter circuit.> > What determines the highest frequency signal an analog solid-state > audio device can input without distortion?The nature of the transistors is the ultimate limit. Because at this limit nonlinearities of a rather terrible nature occur, the circuits they are used in usually limit the frequency with the RC filter mentioned above, or equivalent.> > Analog solid-state audio device = a purely analog electronic device > that can record, store, playback, and process audio signals without > needing any moving parts. > > The above device inputs the electrical signals generated by an > attached microphone. These electric signals are AC and represent the > sound in "electronic" form. Sound with a higher-frequency will > generate a faster-alternating current than sound with a lower- > frequency. A louder sound will generate an alternating-current with a > bigger peak-to-peak wattage than a softer soft. > > What mathematically determines the highest-frequency electric signal > such a device can intake without distortion? >The overall design. Such things as you describe are rare, very, very, very rare. It's very hard to STORE signals purely analog without moving parts. In fact, I had a hard time thinking of any such device that is or was purely analog. However, the old analog storage oscilloscopes would meet your criteria if you don't include electrons in a vacuum as moving parts. There the limit to the frequency response is the size of the focus spot .... i.e. the quality of the lenses! (Such device of course uses analog electron lenses). If you don't intend to store forever, there were things like analog mercury delay lines which stored signals as sound waves travelling through mercury. Doug McDonald
Reply by ●August 20, 20072007-08-20
"Radium" <glucegen1@gmail.com> wrote in message news:1187586671.312439.143710@l22g2000prc.googlegroups.com...> On Aug 19, 8:54 pm, dpl...@radagast.org (Dave Platt) wrote:>> And, in fact, this concept of moving electrical charges is the basis >> for one type of analog signal storage and playback device which has no >> moving (mechanical) parts... the CCD, or Charge Coupled Device. It >> consists of a large number of charge storage devices (typically MOSFET >> transistors with dielectrically-isolated gates) hooked up as a sort of >> shift register or "bucket brigade". Each gate stores a charge which >> is proportional to the input signal present at a given moment in time. >> Several thousand times per second, a clock pulse causes each storage >> cell to generate an output voltage proportional to the charge in its >> storage gate, and then to "capture" onto its gate the signal being >> presented by the previous gate in the chain.Thus introducing an important concept - sampled, non-digital signals. Sampling and digitizing are somewhat independent. The necessary connection comes when you realize that you have to sample something to digitize it. OTOH, you don't have to digitize it when you sample it.> Is CCD a form of analog non-volatile RAM?Yes.>> Why aren't these devices used more than they are? They're not very >> efficient, and they're noisy. Every time the charge is copied from >> one cell to the next, a bit of imprecision (noise) creeps in... so the >> fidelity isn't great. And, because the device has to be able to hold >> a very wide range of charges (since the charge is directly >> proportional to the signal level) the storage gates have to be fairly >> large.Interestingly enough, CCDs are widely used for video. Reason being that their dynamic range is as you say poor for audio, but its OK for video.> I wonder how a PC would perform if it used CCDs in place of digital > storage devices. Lots of errors.Exactly.>> The net result is that an audio CCD is capable of storing a >> decent-quality signal for only a few tens or hundreds of milliseconds, >> from input to output.Only if you have a fairly liberal idea of "decent-quality".> What is the highest frequency an audio CCD can input and output? My > guess is 0.5x the clock rate.Well, a scosh less. Nyquist rules.>> Another sort of a purely analog signal-storage device, with no moving >> parts other than the electrons which convey the signal, is a simple >> length of transmission line (with perhaps some amplifiers mid-way).Ancient computers used quartz delay lines as storage devices. Case in point was the IBM 2848 video display controller. There was one delay line per attached CRTs.> Where is the "storage" in this device?The delay line.>> Put a signal in at one end, get the same signal back out the other end >> some number of microseconds or milliseconds later.> Where is the signal being stored?It was stored in whatever made up the delay line. It could be a rotating disk of magnetic material, a piece of quartz or glass, a bunch of coils and capacitors, whatever. All of these were used up until RAM became an economical solution.
Reply by ●August 20, 20072007-08-20
Floyd L. Davidson wrote:> Jerry Avins <jya@ieee.org> wrote: >> Dave Platt wrote: >>> In article <1187572498.074750.50210@i38g2000prf.googlegroups.com>, >>> Radium <glucegen1@gmail.com> wrote: >>> >>>> I'm curious to why there are no purely-analog devices which can >>>> record, store, and playback electric audio signals [AC currents at > ... > >>> The net result is that an audio CCD is capable of >>> storing a >>> decent-quality signal for only a few tens or hundreds of milliseconds, >>> from input to output. >>> Another sort of a purely analog signal-storage device, >>> with no moving >>> parts other than the electrons which convey the signal, is a simple >>> length of transmission line (with perhaps some amplifiers mid-way). > > ... > >> Come on, Dave, a CCD is a digital device, subject to >> aliasing. > > CCDs are analog devices, with an analog voltage output. > > The fact that they are commonly used as the sensor in > digital cameras results in the output of a CCD virtually > always going directly (well, after a bit of signal > processing for things such as white balance, ISO gain, > etc.) to an analog-to-digital converter that digitizes > the analog signal. > >> The charges represent the signal at a >> particular instant of its average over a particular >> interval. (My CCD digital camera can take time >> exposures.) A CCD's content may not be quantized in >> amount, but it is quantized in time. In a camera, where >> the charges pertain to individual pixels, the result is >> also quantized in space. > > But none of that quantization changes the fact that the > device itself has an analog output.We agree on the facts. We disagree about how to classify borderline cases. Is that important enough to warrant further discussion? Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●August 20, 20072007-08-20
glen herrmannsfeldt wrote:> Dave Platt wrote: > > (snip) > >> As I believe the term "digital" is usually meant, it implies a >> two-state (on/off) storage representation. It's not just that the >> signal amplitude is quantized, but that the quantization uses a >> power-of-two representation and storage system of some sort. > > It means discrete states, but the base does not have to be two. > > Many of the early computers were decimal based, and not > necessarily BCD. > > The Fortran standard still allows for any base greater > than one to be used for representing values.Glenn, I believe that's also a borderline area where definitions become smudged. I know that the Russians built a computer with trinary logic, but all the decimal systems I know, whether BCD, excess-three, or something more exotic, encode the numbers on sets of four wires that carry two-state signals. Making a case that that isn't binary opens the door to claiming that hexadecimal is distinct from binary. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●August 20, 20072007-08-20
"Radium" <glucegen1@gmail.com> wrote in message news:1187586179.764532.267740@i38g2000prf.googlegroups.com...> On Aug 19, 8:34 pm, "Bob Myers" <nospample...@address.invalid> wrote: > >> Sampled analog systems are certainly >> not very common today (unless you count certain forms of >> modulation as "sampling," and in fact there are some very close >> parallels there), but the theory remains the same no matter which >> form of encoding is used. In any event, you must sample the >> original signal at a rate equal to at least twice its bandwidth >> (actually, >> very slightly higher, to avoid a particular degenerate case which >> could occur at EXACTLY 2X the bandwidth) in order to preserve >> the information in the original and avoid "aliasing." > > Is the CCD [Charge Coupled Device] a "sampled analog system"?It's certainly one example of such, being essentially an analog shift register. Bob M.
Reply by ●August 20, 20072007-08-20
Floyd L. Davidson wrote:> Jerry Avins <jya@ieee.org> wrote: >> I like your categories. It is possible in concept to >> have a signal that is quantized in magnitude and >> continuous in time, but (unless we resort to counting >> electrons) I don't think it's possible in practice. > > If you quantize the magnitude, it is digital. That is > by definition.I believe that the definition is flawed. Not that it matters; it's good enough in context. A signal can be quantized without any need to measure it or describe it with a number. An example is the signal being measured in a quantum Hall-effect experiment. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Reply by ●August 20, 20072007-08-20
"Dave Platt" <dplatt@radagast.org> wrote in message news:8ponp4-gfd.ln1@radagast.org...> >Come on, Dave, a CCD is a digital device, subject to aliasing. The >>charges represent the signal at a particular instant of its average over >>a particular interval. (My CCD digital camera can take time exposures.) >>A CCD's content may not be quantized in amount, but it is quantized in >>time. In a camera, where the charges pertain to individual pixels, the >>result is also quantized in space. > > "Digital" and "subject to aliasing" are two different things. > > As I believe the term "digital" is usually meant, it implies a > two-state (on/off) storage representation.Not necessarily; a two-state representation is most properly referred to as "binary." The best definition of "digital" I've managed to come up with comes in the word itself - it is the encoding system whereby information is stored as "digits," i.e., numeric values, as opposed to a system in which the information is stored "analogously" in the form of one parameter (voltage, say) which varies in a like manner as the original. "Quantized" and "sampled" are terms which are really not all that closely associated (at least in theory) with either of the above, although admittedly most systems seen today which employ sampling and/or quantization are also "digital" in the nature of the encoding of the information carried. Bob M.
Reply by ●August 20, 20072007-08-20
nospam@nospam.com (Don Pearce) writes:> [...] > On Mon, 20 Aug 2007 05:46:19 -0800, floyd@apaflo.com (Floyd L. > Davidson) wrote: > >>A "quantized analogue signal" is digital by definition. >> > > No, you haven't. You merely have a signal at a set of discrete levels. > You need an analogue to digital converter to take each of those > quantized levels and convert it into a digital word (of 1s and 0s). > > Digital means "represented by digits", not "in discrete voltage > steps".I've never seen that definition, while I have seen the definition Floyd is proposing, and I think it is a reasonable one. I've also seen many contexts in which "digital" means "discrete-time," i.e., there is no amplitude quantization at all. Take for example any of a number of books on the subject which have "digital signal processing" in the title - they are referring to signals that have been sampled in time, but not quantized (generally, although quantization effects are also analyzed in several such texts). Do you have a reference for your definition? -- % Randy Yates % "I met someone who looks alot like you, %% Fuquay-Varina, NC % she does the things you do, %%% 919-577-9882 % but she is an IBM." %%%% <yates@ieee.org> % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr
