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#42
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Questions about equivalents of audio/video and digital/analog.
Jerry Avins 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. -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
#43
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
Floyd L. Davidson wrote:
(snip) In a digital channel you cannot pass frequencies higher 1/2 the Nyquist rate, which in theory is a very sharp cutoff but in practice it becomes very similar to the gradual analog cutoff. If you read Nyquist's paper, that is pretty much it. He was figuring out for fast he could send pulses through a band limited channel and separate them out at the other end. Electronic communication was digital before it was analog. -- glen |
#44
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
On Mon, 20 Aug 2007 04:57:03 -0800, (Floyd L.
Davidson) wrote: Jerry Avins 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. d -- Pearce Consulting http://www.pearce.uk.com |
#45
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
On 20 Aug., 10:04, (Don Pearce) wrote:
On Mon, 20 Aug 2007 03:51:54 -0400, Jerry Avins wrote: Don Pearce wrote: On Sun, 19 Aug 2007 23:26:16 -0700, (Dave Platt) wrote: "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. 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. My reading of the possible systems goes like this. analogue - a continuous representation of the original signal sampled - a representation of the signal at discrete time points quantized - a sampled signal, but with the possible levels constrained to a limited set of values digital - a quantized signal, with the individual levels represented by numbers Aliasing is going to happen as soon as you move beyond the first line of that list. 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. Yes, I was thinking about that possibility while I was typing, but since I've never come across such a system I decided it would complicate things unnecessarily to include it. Yannis Tsividis once asked in comp.dsp what signal processing practitioners thought of his continuous-time signal processing (filtering) scheme. As I remember, it didn't go down well with the crowd. After reading a paper from him explaining the concept I thought that the scheme had at least educational merit. There are some references on his webpage: http://www.ee.columbia.edu/fac-bios/...s/faculty.html Regards, Andor |
#46
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
(Don Pearce) wrote:
On Mon, 20 Aug 2007 04:57:03 -0800, (Floyd L. Davidson) wrote: Jerry Avins 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. (Emphasis added) QUANTIZATION: A process in which the continuous range of values of an analog signal is sampled and divided into nonoverlapping (but not necessarily equal) subranges, and *a* *discrete*, *unique* *value* *is* *assigned* to each subrange. http://ntia.its.bldrdoc.gov/fs-1037/ -- Floyd L. Davidson http://www.apaflo.com/floyd_davidson Ukpeagvik (Barrow, Alaska) |
#47
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
On Mon, 20 Aug 2007 05:46:19 -0800, (Floyd L.
Davidson) wrote: (Don Pearce) wrote: On Mon, 20 Aug 2007 04:57:03 -0800, (Floyd L. Davidson) wrote: Jerry Avins 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 |
#48
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
On Aug 19, 4:01 pm, Radium 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: |
#49
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
Radium wrote:
On Aug 19, 2:50 pm, (Ray Fischer) wrote: Radium 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 |
#50
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
"Radium" wrote in message oups.com... On Aug 19, 8:54 pm, (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. |
#51
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
Floyd L. Davidson wrote:
Jerry Avins wrote: Dave Platt wrote: In article . com, Radium 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. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
#52
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
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. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
#53
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
"Radium" wrote in message oups.com... On Aug 19, 8:34 pm, "Bob Myers" 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. |
#54
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
Floyd L. Davidson wrote:
Jerry Avins 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. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
#55
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
"Dave Platt" wrote in message ... 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. |
#56
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
(Don Pearce) writes:
[...] On Mon, 20 Aug 2007 05:46:19 -0800, (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." %%%% % 'Yours Truly, 2095', *Time*, ELO http://home.earthlink.net/~yatescr |
#57
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
"Don Pearce" wrote in message ... analogue - a continuous representation of the original signal A CCD is an example of a device which stores information in an analog manner, but non-continuously. Bob M. |
#58
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
"Floyd L. Davidson" wrote in message ... digital - a quantized signal, with the individual levels represented by numbers It makes no difference how the levels are represented. Sure it does. If the levels of the original signal (or rather, whatever parameter of the original information is being recorded/stored/process are represented by analogous levels of some other parameter (e.g., sound represented by voltage), then the system is "analog." It is certainly possible to conceive of a quantized analog system, although such things are rarely if ever seen in practice. "Analog" also does not imply "infinite" precision or adjustability, since, as is the case in ALL systems, the achievable precision (and thus the information capacity) is ultimately limited by noise. See the Gospel According to St. Shannon for further details...;-) Bob M. |
#59
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
"Floyd L. Davidson" wrote in message ... A "quantized analogue signal" is digital by definition. No, Don had it right. A quantized analog signal remains analog as long as the relative values of the quantization levels, one to the other have significance; they thus can carry information, which is the fundamental goal of any such system. Now, we could certainly assign values to those levels which (for instance) are NOT in order from "top to bottom" (or whichever direction you choose to use), which might be done to distribute the susceptibility of any given "bit" in said value to noise evenly. In this case, the levels MUST be interpreted as the intended numeric values in order to recover the original information, and hence this would be a "digital" encoding system. QUANTIZATION: A process in which the continuous range of values of an analog signal is sampled and divided into nonoverlapping (but not necessarily equal) subranges, and *a* *discrete*, *unique* *value* *is* *assigned* to each subrange. http://ntia.its.bldrdoc.gov/fs-1037/ Exactly. But mere quantization by itself does not suffice to render a signal "digitally encoded," no matter what a given government "expert" may claim. Bob M. |
#60
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
Floyd L. Davidson wrote:
(Don Pearce) wrote: On Mon, 20 Aug 2007 04:57:03 -0800, (Floyd L. Davidson) wrote: Jerry Avins 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. (Emphasis added) QUANTIZATION: A process in which the continuous range of values of an analog signal is sampled and divided into nonoverlapping (but not necessarily equal) subranges, and *a* *discrete*, *unique* *value* *is* *assigned* to each subrange. http://ntia.its.bldrdoc.gov/fs-1037/ The government declares it so it must be true? I can demonstrate a circuit using analog components that transforms a continuous ramp input into a staircase output. Moreover, the output levels can be individually adjusted. Is the output digital? (We're discussing an arbitrary definition here. There is no wrong answer.) Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
#61
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
Randy Yates writes:
(Don Pearce) writes: [...] On Mon, 20 Aug 2007 05:46:19 -0800, (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. Let me back-pedal a little and say that, yeah, colloquially, digital is related to "digits." But the term "digital signal" as used in texts and industry does not hold to this colloquial usage. That is, a signal that is completely unquantized in amplitude and represented in base 10 as an element of the real numbers could well be called a digital signal. The key property of such a signal is that it is *discrete-time* (i.e., sampled in time). -- % Randy Yates % "The dreamer, the unwoken fool - %% Fuquay-Varina, NC % in dreams, no pain will kiss the brow..." %%% 919-577-9882 % %%%% % 'Eldorado Overture', *Eldorado*, ELO http://home.earthlink.net/~yatescr |
#62
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
On Mon, 20 Aug 2007 11:31:16 -0400, Randy Yates
wrote: (Don Pearce) writes: [...] On Mon, 20 Aug 2007 05:46:19 -0800, (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. No, it isn't. It misses the fact that sampled and digital are different things. Digits are numbers. 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). Really? Can you point me at something that does DSP on signals that have been merely sampled in time? I've never come across any such thing. Do you have a reference for your definition? Logic will do. If you are doing digital signal processing, you are doing arithmetic on the numbers that come out of an AtoD converter. You can't do that with some voltage levels out of a quantizer. As for discrete time, that is simply sampled, like a class D amplifier, and nothing to do with digits. There is plenty of laziness in the use of nomenclature (as well as misuse by people who simply have no idea what they are talking about). d -- Pearce Consulting http://www.pearce.uk.com |
#63
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
"Radium" wrote in message oups.com... The purpose of this visual "pitch-shifting" is like a way to record/ playback/transmit/receive/store supreme-quality video while using the least bandwidth and storage space necessary when low-pass filtering is not an option. And as you have been told countless times before, you REALLY need to read up on the basics of compression, and specifically the differences between "lossy" and "lossless" compression, and what forces the differences between these two and what enables the latter. Until you do, you'll never really understand any of this. Hence, if you want to get decent imagery in a low-bandwidth imaging device, your best bet is to decrease the spatial frequency because transferring it into the imaging device. Or use fewer bits per sample, or just fewer bits for certain parts of the information you're trying to capture (for instance, chroma information vs. luma), or remove redundant information. (Think about this: how efficient is it, if we have a section of an image which is just a blank white area, to have each and every pixel there carry information that equates to "I'm white!" "So am I!" "So am I".... and so forth? Just one example to consider...). You can also reduce the temporal frequency in the case of motion video. And these are just the simpler approaches. Bob M. |
#64
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
On Mon, 20 Aug 2007 11:46:41 -0400, Randy Yates
wrote: Randy Yates writes: (Don Pearce) writes: [...] On Mon, 20 Aug 2007 05:46:19 -0800, (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. Let me back-pedal a little and say that, yeah, colloquially, digital is related to "digits." But the term "digital signal" as used in texts and industry does not hold to this colloquial usage. That is, a signal that is completely unquantized in amplitude and represented in base 10 as an element of the real numbers could well be called a digital signal. The key property of such a signal is that it is *discrete-time* (i.e., sampled in time). Sorry, but that is simply nonsense. A signal that is sampled in time, but not quantized is an analogue signal. It is treated and processed by analogue circuits. For a signal to be digital its sampled levels must be represented by numbers, which are processed mathematically by some sort of microprocessor. The signal can be reconverted to an analogue one later by a D to A. The output of a D to A is still a time-sampled signal, but since it is now a set of varying levels, we again call it an analogue signal. d -- Pearce Consulting http://www.pearce.uk.com |
#65
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Questions about equivalents of audio/video and digital/analog.
(Don Pearce) writes:
On Mon, 20 Aug 2007 11:31:16 -0400, Randy Yates wrote: (Don Pearce) writes: [...] On Mon, 20 Aug 2007 05:46:19 -0800, (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. No, it isn't. It misses the fact that sampled and digital are different things. Digits are numbers. It isn't reaonable to you. Don't publish opinion as fact. 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). Really? Can you point me at something that does DSP on signals that have been merely sampled in time? I've never come across any such thing. You haven't looked very far. Here is an example (a power calculation): Px = \sum_{n=-\infty}^{+\infty} x^2[n], where x[n] \in \R. Do you have a reference for your definition? Logic will do. If you are doing digital signal processing, you are doing arithmetic on the numbers that come out of an AtoD converter. You can't do that with some voltage levels out of a quantizer. As for discrete time, that is simply sampled, like a class D amplifier, and nothing to do with digits. There is plenty of laziness in the use of nomenclature (as well as misuse by people who simply have no idea what they are talking about). I won't argue that the current usage isn't good nomenclature, but that's the way historically things have developed. -- % Randy Yates % "Though you ride on the wheels of tomorrow, %% Fuquay-Varina, NC % you still wander the fields of your %%% 919-577-9882 % sorrow." %%%% % '21st Century Man', *Time*, ELO http://home.earthlink.net/~yatescr |
#66
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Questions about equivalents of audio/video and digital/analog.
Doug McDonald wrote:
... 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. I mentioned mercury delay lines in an earlier post that probably hadn't seen when you wrote that. There's another way that uses only common electrical components -- capacitors and inductors. Cascaded low-pass T (or pi) sections approximate a transmission line very well up to a frequency determined by the product of 1/LC, while the characteristic impedance is sqrt(L/C). Such "synthetic lines" were staples in telephone research labs. The Bell Labs exhibit at the 1939-40 Worlds Fair included such a line driven by a microphone into which a visitor could speak, feeding headphones (s)he wore while speaking. Most visitors were reduced to stammering by the delay, which I'm guessing was about two seconds; my memory on that point is hazy. I impressed my parents (much like Radium probably impressed his) by doggedly ignoring the feedback and speaking clearly and deliberately. The demonstrator, a Bell Labs researcher, asked us to wait while he fetched his boss to show me off. I do remember being told that delays up to ten seconds were feasible, but that long delays allowed the brain to more easily decouple speech and hearing, so they weren't used in the demo. Bossman showed us the closet where the delay line was stored. The parts were housed in two large relay racks. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
#67
Posted to sci.electronics.basics,rec.video.desktop,comp.dsp,rec.audio.tech,rec.photo.digital
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Questions about equivalents of audio/video and digital/analog.
Don Pearce wrote:
... If you are doing digital signal processing, you are doing arithmetic on the numbers that come out of an AtoD converter. You can't do that with some voltage levels out of a quantizer. Transversal and recursive filters and correlators have been built that operate on unquantized samples. Fourier transforms have been "computed" with lenses. Do you remember the early days of side-looking radar? As for discrete time, that is simply sampled, like a class D amplifier, and nothing to do with digits. There is plenty of laziness in the use of nomenclature (as well as misuse by people who simply have no idea what they are talking about). Agreed. Sometimes I'm guilty of sloppiness. It's the flip side of explanatory excess. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
#68
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Questions about equivalents of audio/video and digital/analog.
On Mon, 20 Aug 2007 12:03:33 -0400, Randy Yates
wrote: (Don Pearce) writes: On Mon, 20 Aug 2007 11:31:16 -0400, Randy Yates wrote: (Don Pearce) writes: [...] On Mon, 20 Aug 2007 05:46:19 -0800, (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. No, it isn't. It misses the fact that sampled and digital are different things. Digits are numbers. It isn't reaonable to you. Don't publish opinion as fact. 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). Really? Can you point me at something that does DSP on signals that have been merely sampled in time? I've never come across any such thing. You haven't looked very far. Here is an example (a power calculation): Px = \sum_{n=-\infty}^{+\infty} x^2[n], where x[n] \in \R. Sorry, but that isn't DSP, it is just calculating the power. Let me put this very simply. If you have a quantized signal and you want to make it twice as big, can you do that with an amplifier, or do you do it mathematically? If the signal is quantized, an amplifier will do it. If it is digitized it won't. You can amplify 0110111001 all you like, you will still have 0110111001. Do you have a reference for your definition? Logic will do. If you are doing digital signal processing, you are doing arithmetic on the numbers that come out of an AtoD converter. You can't do that with some voltage levels out of a quantizer. As for discrete time, that is simply sampled, like a class D amplifier, and nothing to do with digits. There is plenty of laziness in the use of nomenclature (as well as misuse by people who simply have no idea what they are talking about). I won't argue that the current usage isn't good nomenclature, but that's the way historically things have developed. Current usage is just fine. A digital signal is one composed of digits. d -- Pearce Consulting http://www.pearce.uk.com |
#69
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Questions about equivalents of audio/video and digital/analog.
On Mon, 20 Aug 2007 12:42:38 -0400, Jerry Avins wrote:
Don Pearce wrote: ... If you are doing digital signal processing, you are doing arithmetic on the numbers that come out of an AtoD converter. You can't do that with some voltage levels out of a quantizer. Transversal and recursive filters and correlators have been built that operate on unquantized samples. Fourier transforms have been "computed" with lenses. Do you remember the early days of side-looking radar? Quantization isn't important. If you don't quantize all it means is that you are dealing with floating point rather than integer numbers. Still digital of course. I can't think of any floating point ADC's off hand, of course. As for discrete time, that is simply sampled, like a class D amplifier, and nothing to do with digits. There is plenty of laziness in the use of nomenclature (as well as misuse by people who simply have no idea what they are talking about). Agreed. Sometimes I'm guilty of sloppiness. It's the flip side of explanatory excess. Jerry We're all guilty of sloppiness. What is important is that we are able to understand and work with the fine differences when they matter. d -- Pearce Consulting http://www.pearce.uk.com |
#70
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Questions about equivalents of audio/video and digital/analog.
"Randy Yates" wrote in message ... I've never seen that definition, while I have seen the definition Floyd is proposing, and I think it is a reasonable one. No, it isn't. It misses the fact that sampled and digital are different things. Digits are numbers. It isn't reaonable to you. Don't publish opinion as fact. OK, it's not reasonable to ME, either, if you're impressed by taking a vote on this sort of thing. The problem with the definition that you and Floyd seem to want to use is that it leads to several problems in both theory and practice, in addition to the fact that there are numerous counter-examples one can point to. "Reasonable" would seem (at least to me) to mean that you can justify your definition *through reason*, which Don has done. Simply pointing to a published work, including a standard, as a reference to support your definition is what's called an "argument from authority," and it has exactly zero weight in light of an opposing argument based on evidence and logic. However, if you like, I can also point to several references which support the definition that Don and I (and I believe others) are proposing. You might claim the list to be invalid, however, since it would contain works that I myself wrote for publication. Which is, of course, the whole point - simply having your statements published does NOT make them any more or less correct; the deciding factor is whether or not they can be shown to be true through evidence and logic. Bob M. Really? Can you point me at something that does DSP on signals that have been merely sampled in time? I've never come across any such thing. You haven't looked very far. Here is an example (a power calculation): The question was flawed to being with, though - "DSP" stands for "DIGITAL signal processing," which by definition could not have been done on information that was simply "sampled in time." Such information would also have to be digitally encoded in order to be subject to "DSP.: I won't argue that the current usage isn't good nomenclature, but that's the way historically things have developed. A common misuse or misunderstanding does not become less so merely because it IS common. Bob M. |
#71
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Questions about equivalents of audio/video and digital/analog.
On Mon, 20 Aug 2007 10:58:53 -0800, glen herrmannsfeldt
wrote: Don Pearce wrote: (snip) Quantization isn't important. If you don't quantize all it means is that you are dealing with floating point rather than integer numbers. Still digital of course. I can't think of any floating point ADC's off hand, of course. Floating point is still quantized, though not the same as fixed point (integer) data. Effectively it isn't. Of course if you apply this strictly, it is, but a floating point number can be so detailed that it would be essentially impossible to find the quantization steps in the real world. Instead of floating point, Mu-law and A-law coding are commonly used for digitized audio: http://en.wikipedia.org/wiki/Mu_law http://en.wikipedia.org/wiki/A-law_algorithm The result is similar to the use of floating point, but the coding is different. Nonsense. Mu and A law are simply a way of rescuing some decent distortion performance from a limited number of bits by making the quantization steps smaller as the signal gets smaller. The result is lower noise with the penalty of slightly higher distortion. There is no similarity whatever to floating point. d -- Pearce Consulting http://www.pearce.uk.com |
#72
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Questions about equivalents of audio/video and digital/analog.
On 8/20/07 8:41 AM, in article , "Bob Myers"
wrote: "Floyd L. Davidson" wrote in message ... A "quantized analogue signal" is digital by definition. No, Don had it right. A quantized analog signal remains analog as long as the relative values of the quantization levels, one to the other have significance; they thus can carry information, which is the fundamental goal of any such system. No, it becomes a digitally encoded representative of a sample of an analog voltage. First the continuously variable analog signal is sampled, becoming, for example PAM, which is still analog, which is then quantized and may be fit to whatever digital or analog coding that is desired. If it's to a digital code, the signal is digital. If to an analog code, the signal is analog. Now, we could certainly assign values to those levels which (for instance) are NOT in order from "top to bottom" (or whichever direction you choose to use), which might be done to distribute the susceptibility of any given "bit" in said value to noise evenly. In this case, the levels MUST be interpreted as the intended numeric values in order to recover the original information, and hence this would be a "digital" encoding system. QUANTIZATION: A process in which the continuous range of values of an analog signal is sampled and divided into nonoverlapping (but not necessarily equal) subranges, and *a* *discrete*, *unique* *value* *is* *assigned* to each subrange. http://ntia.its.bldrdoc.gov/fs-1037/ Exactly. But mere quantization by itself does not suffice to render a signal "digitally encoded," no matter what a given government "expert" may claim. Bob M. |
#73
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Questions about equivalents of audio/video and digital/analog.
Don Pearce wrote:
... Quantization isn't important. If you don't quantize all it means is that you are dealing with floating point rather than integer numbers. Still digital of course. I can't think of any floating point ADC's off hand, of course. A sample is quantized as soon as it is represented by a finite number of digits. You can't imagine that floating point has infinite resolution. ... Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
#74
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Questions about equivalents of audio/video and digital/analog.
Don Pearce wrote:
On Mon, 20 Aug 2007 10:58:53 -0800, glen herrmannsfeldt wrote: Don Pearce wrote: (snip) Quantization isn't important. If you don't quantize all it means is that you are dealing with floating point rather than integer numbers. Still digital of course. I can't think of any floating point ADC's off hand, of course. Floating point is still quantized, though not the same as fixed point (integer) data. Effectively it isn't. Of course if you apply this strictly, it is, but a floating point number can be so detailed that it would be essentially impossible to find the quantization steps in the real world. Instead of floating point, Mu-law and A-law coding are commonly used for digitized audio: http://en.wikipedia.org/wiki/Mu_law http://en.wikipedia.org/wiki/A-law_algorithm The result is similar to the use of floating point, but the coding is different. Nonsense. Mu and A law are simply a way of rescuing some decent distortion performance from a limited number of bits by making the quantization steps smaller as the signal gets smaller. The result is lower noise with the penalty of slightly higher distortion. There is no similarity whatever to floating point. There's a gap in your understanding. the "segment" is the equivalent of floating point's exponent, and the bits that divide the segment into equal parts are like floating point's mantissa. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
#75
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Questions about equivalents of audio/video and digital/analog.
On Mon, 20 Aug 2007 14:08:11 -0400, Jerry Avins wrote:
Don Pearce wrote: ... Quantization isn't important. If you don't quantize all it means is that you are dealing with floating point rather than integer numbers. Still digital of course. I can't think of any floating point ADC's off hand, of course. A sample is quantized as soon as it is represented by a finite number of digits. You can't imagine that floating point has infinite resolution. Sure, but you may be quantizing to many trillions of finer steps, so that effectively the thing is almost not quantized. d -- Pearce Consulting http://www.pearce.uk.com |
#76
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Questions about equivalents of audio/video and digital/analog.
glen herrmannsfeldt wrote in
: Bob Myers wrote: (snip) "Analog" also does not imply "infinite" precision or adjustability, since, as is the case in ALL systems, the achievable precision (and thus the information capacity) is ultimately limited by noise. See the Gospel According to St. Shannon for further details...;-) How about, Analog implies "infinite" precision in the absence of noise, including fundamental quantum noise. Note, for example, that an analog current is quantized in units of the charge on the electron. -- glen Doesn't "analog" also imply that x(t) exists for all t in range, and not just at nT for all n in range? Or would people just call that "sampled"? -- Scott Reverse name to reply |
#77
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Questions about equivalents of audio/video and digital/analog.
Radium's ability to suck so many people into attempting to
answer insane questions is reaching legendary heights. I hereby nominate him for the Troll Hall of Fame with special endorsement for use of technical gobeldygook. |
#78
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Questions about equivalents of audio/video and digital/analog.
Don Pearce wrote:
(snip) Quantization isn't important. If you don't quantize all it means is that you are dealing with floating point rather than integer numbers. Still digital of course. I can't think of any floating point ADC's off hand, of course. Floating point is still quantized, though not the same as fixed point (integer) data. Instead of floating point, Mu-law and A-law coding are commonly used for digitized audio: http://en.wikipedia.org/wiki/Mu_law http://en.wikipedia.org/wiki/A-law_algorithm The result is similar to the use of floating point, but the coding is different. -- glen |
#79
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Questions about equivalents of audio/video and digital/analog.
glen herrmannsfeldt wrote:
Jerry Avins wrote: (snip) 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. I believe that some of the early machines used 10 wires. With ten neon lamps stacked vertically for each digit at first, then Nixie tubes. Biquinary, with seven wires, one of two and one of five, has also been used. That was so entrenched that TI's first IC decimal counter could be configured as a biquinary device. It had divide-by-two and divide-by-five sections. In both cases each wire has one of two values, but it isn't very "binary like". It really depends on context. From a circuit viewpoint, I think of "binary" as implying a single receiver threshold. Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ |
#80
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Questions about equivalents of audio/video and digital/analog.
On Mon, 20 Aug 2007 11:58:32 -0700, "Richard Crowley"
wrote: Radium's ability to suck so many people into attempting to answer insane questions is reaching legendary heights. I hereby nominate him for the Troll Hall of Fame with special endorsement for use of technical gobeldygook. I vote: aye -- Official website "Jonah's Quid" http://www.jonahsquids.co.uk |
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